Category: Quiz

Histones

HISTONES


Histones

  • Most abundant chromatin Protein.
  • Histones are divided into-
  1. Core Histone
  2. Linker Histone
  • 5 classes- H1, H2A, H2B (Lysine), H3 and H4 (arginine).
  • Linker histone- is loosely bound to nucleosome.
  • Modifications-
  1. Acetylation of H3 & H4
  2. Acetylation of histones associated with chromosomal assembly during DNA replication.
  3. Phosphorylation of H1 is associated with condensation of chromosome during replication.
  4. Methylation correlated with activation or repression of gene transcription.
  • Chromatins are of two types-
  • Euchromatin- Transcriptionally active chromatin and is uncondensed. Chromatins are less stained.
  • Heterochromatin- Transcriptionally inactive, chromatin stains densely, chromatin densely packed. 2 types-
  1.  Constitutive- seen in centromere and chromosomal ends of the telomere.
  2.  Facultative
  • Chromosomes-
  •  In humans, there are 23 pairs of chromosomes.
  •  The position of centromere is the characteristic mark for specific chromosome.
  •  The centromere is AT rich region.
  • Total number of chromosome in humans is 46 (23 pairs).
  • The number of base pairs in haploid set of chromosome is 3.0 x 1O9 (3 billion bp)
  • Percentage of exons in human genome is approximately 1.14% (1.5-2%)
  • The number of protein coding genes in human genome is 20,687.
  • The genes account for 10-15% of DNA.

Exam Important

  • Total number of chromosome in humans is 46 (23 pairs).
  • The number of base pairs in haploid set of chromosome is 3.0 x 1O9 (3 billion bp)
  • Percentage of exons in human genome is approximately 1.14% (1.5-2%)
  • The number of protein coding genes in human genome is 20,687.
  • The genes account for 10-15% of DNA.
  • Euchromatin is transcriptionally active and heterochromatin is transcriptionally inactive.
  • For euchromatin, chromatin is less densely packed.
  • For heterochromatin, chromatin is densely packed.
Don’t Forget to Solve all the previous Year Question asked on HISTONES

Module Below Start Quiz

Organization of DNA in the cell

Organization of DNA in the cell

Q. 1

Total number of base pairs in human haploid set of chromosome

 A

3 million

 B

3 billion

 C

33 billion

 D

5 million

Q. 1

Total number of base pairs in human haploid set of chromosome

 A

3 million

 B

3 billion

 C

33 billion

 D

5 million

Ans. B

Explanation:

  • Humanhaploid genome of each cell consist of (3*109 ) bp (3 billion bp)
  • Current estimates predict 20,687 protein coding genes
  •  Exome constitutes 7.74% of genome
  • SNPs estimated is 10 million.

Q. 2

Proteins seen in chromosomes are called

 A

Nucleotides

 B

Histones

 C

Apoproteins

 D

Glycoproteins

Q. 2

Proteins seen in chromosomes are called

 A

Nucleotides

 B

Histones

 C

Apoproteins

 D

Glycoproteins

Ans. B

Explanation:

Histones are the most abundant histone proteins.

Quiz In Between



Bile acid synthesis

Bile Acid Synthesis

Q. 1

Secondary bile acids are synthesised by:

 A

Liver

 B

Intestine

 C

Both liver and intestine

 D

Pancreas

Q. 1

Secondary bile acids are synthesised by:

 A

Liver

 B

Intestine

 C

Both liver and intestine

 D

Pancreas

Ans. B

Explanation:

Bile acids are synthesized in the liver.

Bile acids are divided into primary or secondary: Primary bile acids are synthesized in the liver and secondary bile acids are synthesized from primary bile acids in the intestine by colonic bacteria. 
Ref: Harrison, E-18, P-2461.

Q. 2

The four major bile acids found in humans are synthesized from:

 A

Cholesterol

 B

Amino acids

 C

Bilirubin

 D

Protein

Q. 2

The four major bile acids found in humans are synthesized from:

 A

Cholesterol

 B

Amino acids

 C

Bilirubin

 D

Protein

Ans. A

Explanation:

When considering bile as a digestive secretion, it is the bile acids that represent the most important components. They are synthesized from cholesterol and secreted into the bile conjugated to glycine or taurine, a derivative of cysteine. 

Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 25. Overview of Gastrointestinal Function & Regulation. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.

Q. 3

Bile acid synthesized in liver (primary bile acids) is:

 A

Lithocholic acid

 B

Cholic acid

 C

Deoxycholic acid

 D

All of the above

Q. 3

Bile acid synthesized in liver (primary bile acids) is:

 A

Lithocholic acid

 B

Cholic acid

 C

Deoxycholic acid

 D

All of the above

Ans. B

Explanation:

 

Bile acids

  • They are steroid acids found predominantly in the bile.
  • Bile acid refers to the protonated (-COOH) form.
  • ile salt refers to the deprotonated or ionized (-COO-) form.
  • Bile salts are bile acids compounded with a cation, usually sodium.
  • The salts of taurocholic acid and glycocholic acid (derivatives of cholic acid) represent approximately eighty percent of all bile salts.
  • The two primary bile acids are cholic acid, and chenodeoxycholic acid.
  • Bile acids, glycine and taurine conjugates, and 7-alpha-dehydroxylated derivatives (deoxycholic acid and lithocholic acid) are all found in intestinal bile.
  • The increase in bile flow is exhibited with an increased secretion of bile acids.
  • e main function of bile acid is to facilitate the formation of micelles, which promotes processing of dietary fat
  • Bile acids are made in the liver by the cytochrome P450-mediated oxidation of cholesterol.
  • They are conjugated with taurine or the amino acid glycine, or with a sulfate or a glucuronide, and are then stored in the gallbladder, which concentrates the salts by removing the water.
  • Rate limiting step is the addition of a hydroxyl group on position 7 of the steroid nucleus by the enzyme cholesterol 7 alpha-hydroxylase.
  • Upon eating a meal, the contents of the gallbladder are secreted into the intestine, where bile acids serve the purpose of emulsifying dietary fats.
  • Bile acids serve other functions, including eliminating cholesterl from the body, drivin the ow of bile to eliminabte catabolites from the liver, emulsifying lipids and fat soluble vitamins in the intestine g to form micelles thatt. can be transported via the lacteal system, and aiding in the reduction of the bacteria flora found in the smal intes ine a biliary tract.

Conjugated bile acids are more efficient at emulsifying fats because at intestinal pH, they are more ionized than unconjugated bile acs.

  • The body produces about 800 mg of cholesterol per day and about half of that is used for bile acid synthesis.
  • In total about 20-30 grams of bile acids are secreted into the intestine daily.

About 90% of excreted bile acids are reabsorbed by active transport in theileum and recycled in what is referred to as the enterohepatic circulation which moves the bile salts from the intestinal system back to the liver and the gallbladder.


Q. 4

Bile acids are reabsorbed from ‑

 A

Duodenum

 B

Proximal jejunum

 C

Distal jejunum

 D

Ileum

Q. 4

Bile acids are reabsorbed from ‑

 A

Duodenum

 B

Proximal jejunum

 C

Distal jejunum

 D

Ileum

Ans. D

Explanation:

Ans. is ‘d’ i.e., Ileum

Quiz In Between


Q. 5

Bile acids are synthesized from ‑

 A

Heme

 B

Cholesterol

 C

Ribulose

 D

Arachidonic acid

Q. 5

Bile acids are synthesized from ‑

 A

Heme

 B

Cholesterol

 C

Ribulose

 D

Arachidonic acid

Ans. B

Explanation:

Ans. is ‘b’ i.e., Cholesterol

  • Primary bile acids are cholic acid and chenodeoxycholic acid, which are synthesized from cholesterol in liver.
  • In the intestine some of the primary bile acids are converted into secondary bile acids, i.e., deoxycholic acid (formed from cholic acid) and lithocholic acid (derived from chenodexoxycholic acid).
  • Glycine and taurine conjugates of these bile acids are called as bile salts.
  • For example, cholic acid is a bile acid, and its glycine conjugate (glycocholic acid) is a bile salt.
  • Bile salts help in digestion and absorption of fat by emulsification and micelles formation.
  • Bile salts act as detergents, i.e., they have surface tension lowering action.
  • Detergent action is due to amphipathic nature of bile salts (Note : Amphipathic molecules are molecules that contain both hydrophobic non-polar as well as hydrophilic-polar ends).



Q. 6

Rate limiting enzyme in bile acid synthesis ‑

 A

Desmolase

 B

21 α-hydroxylase

 C

7α-hydroxylase

 D

12α-hydroxylase

Q. 6

Rate limiting enzyme in bile acid synthesis ‑

 A

Desmolase

 B

21 α-hydroxylase

 C

7α-hydroxylase

 D

12α-hydroxylase

Ans. C

Explanation:

Ans. is ‘c’ i.e., 7α-hydroxylase

About half of the cholesterol in the body is ultimately metabolized to bile acids.

The primary bile acids are synthesized from cholesterol in liver. These are cholic acid and chenodeoxycholic acid.

Rate limiting enzyme in primary bile acids synthesis is 7α – hydroxylase (cholesterol 7α – hydroxylase).

This enzyme is inhibited by bile acids and induced by cholesterol.

Thyroid hormones induce transcription of 7a-hydroxylase, thus in patients with hypothyroidism plasma cholesterol tends to rise (because of inhibition of 7α-hydroxylase which in turn inhibits conversion of cholesterol to bile acids).


Q. 7

Which of the following is/are bile acids?

 A

Cholic acid

 B

Lithocholic acid

 C

Deoxycholic acid

 D

All of the above

Q. 7

Which of the following is/are bile acids?

 A

Cholic acid

 B

Lithocholic acid

 C

Deoxycholic acid

 D

All of the above

Ans. D

Explanation:

 

Primary bile acids are cholic acid and chenodeoxycholic acid, which are synthesized from cholesterol in liver. In the intestine some of the primary bile acids are converted into secondary bile acids, i.e., deoxycholic acid (formed from cholic acid) and lithocholic acid (derived from chenodexoxycholic acid).

  • Glycine and taurine conjugates of these bile acids are called as bile salts. For example, cholic acid is a bile acid, and its glycine conjugate (glycocholic acid) is a bile salt.
  • Bile salts = Sodium or potassium + Amino acid (glycine or taurine) + Bile acids (Cholic acid or chenodeoxycholic acid)
  • So, Bile salts are : –
  • Sodium + glycine + cholic acid = Sodium-glyco-cholic acid (sodium-glyco-cholate)
  • Sodium + taurine + cholic acid = Sodium-tauro-cholic acid (Sodium-tauro-cholate)
  • Sodium + glycine + chenodeoxycholic aicd = Sodium-glyco-chenodeoxycholate
  • Sodium + taurine + chenodeoxycholic acid = Sodium-tauro-chenodeoxycholate o Similarly potassiun bile salts are potassium-glycocholate, potassium-taurocholate, potassium-glyco­chenodexoxycholate, and potassium-tauro-chenodexoxycholate.

Q. 8

Primary bile acid is‑

 A

Deoxycholic acid

 B

Lithocholic acid

 C

Chenodeoxycholic acid

 D

None

Q. 8

Primary bile acid is‑

 A

Deoxycholic acid

 B

Lithocholic acid

 C

Chenodeoxycholic acid

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Chenodeoxycholic acid 

  • Primary bile acids are cholic acid and chenodeoxycholic acid, which are synthesized from cholesterol in liver. In the intestine some of the primary bile acids are converted into secondary bile acids, i.e., deoxycholic acid (formed from cholic acid) and lithocholic acid (derived from chenodexoxycholic acid).
  • Glycine and taurine conjugates of these bile acids are called as bile salts. For example, cholic acid is a bile acid, and its glycine conjugate (glycocholic acid) is a bile salt.

Quiz In Between



Metabolism Of Purine

METABOLISM OF PURINE

Q. 1 The purines salvage pathway is for:
 A Hypoxanthine and Xanthine
 B Hypoxanthine andAdenine
 C Adenine and Guanine
 D Xanthine and Guanine
Q. 1 The purines salvage pathway is for:
 A Hypoxanthine and Xanthine
 B Hypoxanthine andAdenine
 C Adenine and Guanine
 D Xanthine and Guanine
Ans. B

Explanation:

Hypoxanthine andAdenine


Q. 2

In humans, the end product of purine metabolism is uric acid. End product of purine metabolism in non-primate mammals is:

 A

Uric acid

 B

Ammonia

 C

Urea

 D

Allantoin

Q. 2

In humans, the end product of purine metabolism is uric acid. End product of purine metabolism in non-primate mammals is:

 A

Uric acid

 B

Ammonia

 C

Urea

 D

Allantoin

Ans. D

Explanation:

Humans convert adenosine and guanosine to uric acid. Adenosine is first converted to inosine by adenosine deaminase. In mammals other than higher primates, uricase converts uric acid to the water-soluble product allantoin. However, since humans lack uricase, the end product of purine catabolism in humans is uric acid.  

Ref: Rodwell V.W. (2011). Chapter 33. Metabolism of Purine & Pyrimidine Nucleotides. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.  

Q. 3

Nucleoside is made up of:

1. Pyrimidine
2. Histone
3. Sugar
4. Purine
5. Phosphate

 A

1,2 & 3

 B

1,3 & 4

 C

1,3 & 5

 D

2,3 & 4

Q. 3

Nucleoside is made up of:

1. Pyrimidine
2. Histone
3. Sugar
4. Purine
5. Phosphate

 A

1,2 & 3

 B

1,3 & 4

 C

1,3 & 5

 D

2,3 & 4

Ans. B

Explanation:

“The nucleoside is composed of purine purine or pyrimidine base linked to either D-ribose (in RNA) or D-2- deoxyribose (in DNA)”

“The nuclear DNA is found bounded to basic proteins called histones”.
Nucleotides
  • Nucleotides are nucleoside +P
  • The Phosphodiester bond between the nucleotides is formed mainly between 3’OH group of sugar of one nucleotide to 3’OH group of sugar of another nucleotide.

 

Ref: Harper 27/e, Page 297; Chatterjee & shinde 7/e, Page 206-07.

Quiz In Between


Q. 4

Which among the following are the substrates needed for purine salvage pathway?

 A

Hypoxanthine and Xanthine

 B

Hypoxanthine and Adenine

 C

Adenine and Guanine

 D

Xanthine and Guanine

Q. 4

Which among the following are the substrates needed for purine salvage pathway?

 A

Hypoxanthine and Xanthine

 B

Hypoxanthine and Adenine

 C

Adenine and Guanine

 D

Xanthine and Guanine

Ans. B

Explanation:

Conversion of purines, their ribonucleosides, and their deoxyribonucleosides to mononucleotides involves “salvage reactions”.
The more important mechanism involves phosphoribosylation by PRPP of a free purine (Pu) to form a purine 5′-mononucleotide (Pu-RP). Phosphoryl transfer from ATP, catalyzed by adenosine- and hypoxanthine-phosphoribosyl transferases, converts adenine, hypoxanthine, and guanine to their mononucleotides. 
 
A second salvage mechanism involves phosphoryl transfer from ATP to a purine ribonucleoside. Phosphorylation of the purine nucleotides, catalyzed by adenosine kinase, converts adenosine and deoxyadenosine to AMP and dAMP. Similarly, deoxycytidine kinase phosphorylates deoxycytidine and 2′-deoxyguanosine, forming dCMP and dGMP.
 
Ref: Rodwell V.W. (2011). Chapter 33. Metabolism of Purine & Pyrimidine Nucleotides. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

 


Q. 5

End product of purine metabolism in non-primate mammals is:

 A

Uric acid

 B

Ammonia

 C

Urea

 D

Allantoin

Q. 5

End product of purine metabolism in non-primate mammals is:

 A

Uric acid

 B

Ammonia

 C

Urea

 D

Allantoin

Ans. D

Explanation:

D i.e. Allantoin


Q. 6

Which of the following RNA has abnormal purine bases:

 A

t-RNA

 B

m-RNA

 C

r-RNA

 D

16S RNA

Q. 6

Which of the following RNA has abnormal purine bases:

 A

t-RNA

 B

m-RNA

 C

r-RNA

 D

16S RNA

Ans. A

Explanation:

A i.e. tRNA

Quiz In Between


Q. 7

Amino acid which contributes to biosynthesis of purine ribonucleotide are all except:    

 A

Aspartate

 B

Histidine

 C

Glutamine

 D

Glycine

Q. 7

Amino acid which contributes to biosynthesis of purine ribonucleotide are all except:    

 A

Aspartate

 B

Histidine

 C

Glutamine

 D

Glycine

Ans. B

Explanation:

 

Biosynthesis of purine

  • N1 of purine is derived from amino group of aspartate
  • N3 and N9 are obtained from amide group of glutamine
  • C4, C5 and N7 of the purine ring of nucleotides are contributed by glycine



Q. 8

Final product of purine metabolism is:

 A

Uric acid

 B

Creatinine

 C

Xanthine

 D

Phoshphates

Q. 8

Final product of purine metabolism is:

 A

Uric acid

 B

Creatinine

 C

Xanthine

 D

Phoshphates

Ans. A

Explanation:

 

Nucleotides are derived from biosynthetic precursors of carbohydrate and amino acid metabolism, and from ammonia and carbon dioxide.

The liver is the major organ of de novo synthesis of all four nucleotides.

Degradation in humans, however, is only complete for pyrimidines (C, T, U), but not purines (G, A), which are excreted from the body in form of uric acid



Q. 9

Nitrogen-9 of purine ring is provided by ‑

 A

Glycine

 B

Aspartate

 C

Glutamine

 D

CO2

Q. 9

Nitrogen-9 of purine ring is provided by ‑

 A

Glycine

 B

Aspartate

 C

Glutamine

 D

CO2

Ans. C

Explanation:

 

In de novo synthesis, purine ring is formed from variety of precursors is assembled on ribose-5-phosphate. Precursors for de novo synthesis are –

i)      Glycine provides C4, C5 and N7

ii)     Aspartate provides N1

iii)    Glutamine provides N3 and N9

iv)   Tetrahydrofolate derivatives furnish C2 and C8

v)    Carbon dioxide provides C6

Quiz In Between


Q. 10

First product of purine metabolism

 A

Uric acid

 B

Xanthine

 C

P-alanine

 D

CO2

Q. 10

First product of purine metabolism

 A

Uric acid

 B

Xanthine

 C

P-alanine

 D

CO2

Ans. B

Explanation:

 

  • Humans catabolize purines to uric acid.
  • But, first purines are catabolized to xanthine, which is further catabolized to purine.

Q. 11

First purine nucleotide, which is synthesized in purine biosynthesis ‑

 A

AMP

 B

GMP

 C

IMP

 D

UMP

Q. 11

First purine nucleotide, which is synthesized in purine biosynthesis ‑

 A

AMP

 B

GMP

 C

IMP

 D

UMP

Ans. C

Explanation:

 

The biosynthesis of purine begins with ribose-5-phosphate, derived from pentose phosphate pathway (PPP).

First intermediate formed in this pathway, 5-phosphoribosyl-pyrophosphate (PRPP), is also an intermediate in purine salvage pathway.


Q. 12

Salvage pathway of purine biosynthesis is important for ‑

 A

Liver

 B

RBCs

 C

Kidney

 D

Lung

Q. 12

Salvage pathway of purine biosynthesis is important for ‑

 A

Liver

 B

RBCs

 C

Kidney

 D

Lung

Ans. B

Explanation:

 

Purine nucleotide synthesis occurs by two pathways :

1.De novo synthesis

2.Salvage pathway

Liver is the major site of purine nucleotide biosynthesis (de novo).

Certain tissues cannot synthesize purine nucleotides by de novo patyway, e g. brain, erythrocytes and polymor­phonuclear leukocytes.

These are dependent on salvage pathway for synthesis of purine nucleotides by using exogenous purines, which are formed by degradation of purine nucleotides synthesized in liver.

Quiz In Between


Q. 13

Purine metabolism produces –

 A

β – alanine

 B

NH3

 C

CO2

 D

Uric acid

Q. 13

Purine metabolism produces –

 A

β – alanine

 B

NH3

 C

CO2

 D

Uric acid

Ans. D

Explanation:

Ans. is ‘d’ i.e., Uric acid


Q. 14

PRPP glutamyl amidotransferase is increased to increase purine synthesis in ‑

 A

Liver

 B

RBC

 C

Brain

 D

Polymorphs

Q. 14

PRPP glutamyl amidotransferase is increased to increase purine synthesis in ‑

 A

Liver

 B

RBC

 C

Brain

 D

Polymorphs

Ans. A

Explanation:

 

PRPP glutamyl amidotransferase is one of the rate limiting enzyme in de novo synthesis of purines. o The de novo synthesis of purines is most active in liver.

Brain, RBCs (erythrocytes) and polymorphonuclear leokocytes (polymorphs) cannot synthesize purine nucleotides by de novo pathway.

Biosynthesis of purine neucleotides

Two important purine nucleotides are synthesized : (i) adenosine monophosphate (AMP) and (ii) guanosine monophosphate (GMP). Then AMP and GMP are converted to other purine nucleotides like ADP, ATP, GDP, GTP etc. Purine nucleotides can be synthesized by two pathways – (I) De novo synthesis and (2) Salvage pathway.

De novo pathway (De novo synthesis)

In de novo pathway, the purine nucleotides are synthesized from amphibolic intermediates. Amphibolic intermediates are the intermediary metabolites of amphibolic pathways (eg. citric acid cycle) which have dual purposes, i e. they serve in catabolism as well as in anabolism.

In de novo synthesis, purine ring is formed from variety of precursors is assembled on ribose-5-phosphate. Precursors for de novo synthesis are

i)  Glycine provides C4 C5 and N7

ii)  Aspartate provides NI

iii)  Glutamine provides N3 and N9

iv)  Tetrahydrofolate derivatives furnish C2 and Cs

v)  Carbon dioxide provides C6


Q. 15

Salvage pathway of purine nucleotide synthesis are used by all except ‑

 A

Brain

 B

Liver

 C

RBC

 D

Leukocytes

Q. 15

Salvage pathway of purine nucleotide synthesis are used by all except ‑

 A

Brain

 B

Liver

 C

RBC

 D

Leukocytes

Ans. B

Explanation:

 

Purine nucleotide synthesis occurs by two pathways :-

1.De novo synthesis

2.Salvage pathway

Liver is the major site of purine nucleotide biosynthesis (de novo).

Certain tissues cannot synthesize purine nucleotides by de novo patyway, e g. brain, erythrocytes and polymorphonuclear leukocytes.

These are dependent on salvage pathway for synthesis of purine nucleotides by using exogenous purines, which are formed by degradation of purine nucleotides synthesized in liver.

Quiz In Between


Q. 16

Salvage pathway of purine nucleotide synthesis are used by all except ‑

 A

Brain

 B

Liver

 C

RBC

 D

Leukocytes

Q. 16

Salvage pathway of purine nucleotide synthesis are used by all except ‑

 A

Brain

 B

Liver

 C

RBC

 D

Leukocytes

Ans. B

Explanation:

Ans. is ‘b’ i.e., Liver

  • Purine nucleotide synthesis occurs by two pathways :
  • De novo synthesis
  • Salvage pathway
  • Liver is the major site of purine nucleotide biosynthesis (de novo).
  • Certain tissues cannot synthesize purine nucleotides by de novo patyway, e g. brain, erythrocytes and polymorphonuclear leukocytes.
  • These are dependent on salvage pathway for synthesis of purine nucleotides by using exogenous purines, which are formed by degradation of purine nucleotides synthesized in liver.

Q. 17

In humans, end product of purine metabolism 

 A

Allantoin

 B

Uric acid

 C

CO2

 D

None

Q. 17

In humans, end product of purine metabolism 

 A

Allantoin

 B

Uric acid

 C

CO2

 D

None

Ans. B

Explanation:

Ans. is ‘b’ i.e., Uric acid


Q. 18

Salvage purine synthesis refers to ‑

 A

Synthesis of purine from ribose-5-phosphate

 B

Synthesis of purine from pyrimidine

 C

Synthesis of purine nucleotides from purine bases

 D

None of the above

Q. 18

Salvage purine synthesis refers to ‑

 A

Synthesis of purine from ribose-5-phosphate

 B

Synthesis of purine from pyrimidine

 C

Synthesis of purine nucleotides from purine bases

 D

None of the above

Ans. C

Explanation:

Ans. is ‘c’ i.e., Synthesis of purine nucleotides from purine bases

  • Two important purine nucleotides are synthesized : (i) adenosine monophosphate (AMP) and (ii) guanosine monophosphate (GMP). Then AMP and GMP are converted to other purine nucleotides like ADP, ATP, GDP, GTP etc. Purine nucleotides can be synthesized by two pathways – (1) De novo synthesis and (2) Salvage pathway. De novo pathway (De novo synthesis)
  • In de novo pathway, the purine nucleotides are synthesized from amphibolic intermediates. Amphibolic intermediates are the intermediary metabolites of amphibolic pathways (eg. citric acid cycle) which have dual purposes, i e. they serve in catabolism as well as in anabolism.
  • In de novo synthesis, purine ring is formed from variety of precursors is assembled on ribose-5-phosphate. Precursors for de novo synthesis are ‑
  1. Glycine provides Ca, C5 and N7
  2. Aspartate provides N,
  3. Glutamine provides N3 and N9
  4. Tetrahydrofolate derivatives furnish C2 and C8
  5. Carbon dioxide provides Co

Salvage pathway of purine nucleotide synthesis

  • Free purine bases (adenine, guanine and hypoxanthine) and purine nucleosides are formed in cells during the metabolic degradation of nucleic acids and nucleotides.
  • These free purine bases and purine nucleosides are reused in the formation of purine nucleotides. 
  • This is called salvage pathway (salvage means property saved from loss).
  • Salvage synthesis requires far less energy than de novo synthesis.

Quiz In Between



Hemochromatosis

Hemochromatosis

Q. 1

MOST common mutation seen in heriditary hemochromatosis is:

 A

C282Y

 B

H63D

 C

TFR2

 D

SLC11A3

Q. 1

MOST common mutation seen in heriditary hemochromatosis is:

 A

C282Y

 B

H63D

 C

TFR2

 D

SLC11A3

Ans. A

Explanation:

The most common mutation in hereditary hemochromatos is a homozygous G to A mutation resulting in a cysteine to tyrosine substitution at position 282 (C282Y). Another relatively common  mutation (H63D) results in a substitution of histidine to aspartic acid at codon 63.

Mutations like  transferrin receptor 2 TFR2 mutation and  ferroportin 1 gene, SLC11A3 mutation are rare.

Ref: Harrisons principles of internal medicine, 18th edition, Page: 3162


Q. 2

Which of the following condition is not true about Hemochromatosis?

 A

Hypogonadism

 B

Arthropathy

 C

Diabetes mellitus

 D

Desferrioxamine is treatment of choice

Q. 2

Which of the following condition is not true about Hemochromatosis?

 A

Hypogonadism

 B

Arthropathy

 C

Diabetes mellitus

 D

Desferrioxamine is treatment of choice

Ans. D

Explanation:

Phlebotomy is the treatment of choice of hemochromatosis. Chelating agent desferrioxamine is indicated when anemia or hypoproteinemia is severe enough to preclude phlebotomy.

Hemochromatosis is a common inherited disorder of iron metabolism in which dysregulation of intestinal iron absorption results in deposition of excessive amounts of iron in parenchymal cells resulting in tissue damage and organ dysfunction.

Liver is the first organ to be affected and hepatomegaly is seen in more than 95% of patients. Diabetes mellitus occur in 65% of patients with advanced disease. Arthropathy is seen in 20-25% of symptomatic patients. Second and third metacarpophalangeal joints are the first joints to be involved.

Manifestations of hypogonadism includes loss of libido, impotence, amenorrhea, testicular atrophy and gynecomastia. Most common cardiac manifestation is congestive heart failure.


Q. 3

Hemochromatosis is a defect in metabolism of

 A

Iron

 B

Copper

 C

Magnesium

 D

Calcium

Q. 3

Hemochromatosis is a defect in metabolism of

 A

Iron

 B

Copper

 C

Magnesium

 D

Calcium

Ans. A

Explanation:

Ans. is `a’ i.e., Iron

o Hemochromatosis is characterized by the excessive accumulation of body iron, most of which is deposited in parenchymal organs such as the liver and pancreas.

Quiz In Between


Q. 4

The first test to become positive in patients with Hemochromatosis is:

 A

Increased Serum Iron

 B

Increased Serum Ferritin

 C

Increased Transferrin Saturation

 D

Increased Liver Enzymes

Q. 4

The first test to become positive in patients with Hemochromatosis is:

 A

Increased Serum Iron

 B

Increased Serum Ferritin

 C

Increased Transferrin Saturation

 D

Increased Liver Enzymes

Ans. C

Explanation:

Answer is C (Increased Transferrin Saturation):

Transferrin Saturation is the first blood test to become elevated in Hemochromatosis.

The first biochemical manifestation of hemochromatosis is an increase of transferring saturation, which reflects an uncontrolled influx of iron into the blood stream .from enterocytes and macrophages.

The serum transferrin saturation and serum ferritin levels are the two most important indicators of hemochromatosis and body iron stores.

Elevation of transferrin levels precedes elevation offerritin levels.

The first biochemical manifestation of hetnochromatosis is an increase in serum transferrin saturation.

Serum iron concentration per se is not a good indicator for iron overload states like Hemochromatosis.

Liver Enzymes may be normal or elevated depending on the extent of hepatocyte damage.

They are usually normal or only mildly elevated in the early stages of hemochromatosis.

Laboratory findings in Hemochromatosis

Transferrin saturation is the first blood test to become elevated in hemochromatosis homozygotes

The sensitivity of elevated transferring saturation to identify a patient with hemochromatosis is 94 to 98% and its specificity is 70 to 98%.

Transferrin saturation is usually > 60% in symptomatic men and >50% in symptomatic women

  • Unbound
  • Serum
  • Liver

DNA testing by polymerase chain reaction may he used to detect mutations of the HFE gene.


Q. 5

All of the following statements about hereditary hemochromatosis are true Except

 A

Arthropathy involving small joints of hands may be seen

 B

Skin pigmentation is a frequent presentation

 C

Desferroxamine is the treatment of choice

 D

Hypogonadism may be seen

Q. 5

All of the following statements about hereditary hemochromatosis are true Except

 A

Arthropathy involving small joints of hands may be seen

 B

Skin pigmentation is a frequent presentation

 C

Desferroxamine is the treatment of choice

 D

Hypogonadism may be seen

Ans. C

Explanation:

Answer is C (Desferroxamine is the treatment of choice):

The therapy of hematochromatosis involves removal of excess body iron Iron removal is best acieved by periodic phlebotomies which is the treatment of choice for Hematochromosis.

Chelating agents like desferoxamine are less effective and indicated when anemia or hypoproteinemia is severe enough to preclude phlebotomy (Harrison.

Chelatingagents are not the treatment of choice for Hematochromatosis.


Q. 6

All are seen in hemochromatosis except‑

 A

Hypogonadism

 B

Arthropathy

 C

Bronze diabetes

 D

Desferrioxamine is the treatment of choice

Q. 6

All are seen in hemochromatosis except‑

 A

Hypogonadism

 B

Arthropathy

 C

Bronze diabetes

 D

Desferrioxamine is the treatment of choice

Ans. D

Explanation:

Answer is D (Desferrioxamine is the treatment of choice):

The treatment of choice for Hematochromatosis is removed of excess body iron by Phlebotomy and not with the use of chelating agents like desfernoxamine.

Removal of Excessive Body iron

  • Phlebotomy is the treatment of choice  Iron removal is best accomplished by once or twice weekly phlebotomy of 500m1,

– These should be continued until the serum ferritin level is < 50pg/L (May be required for 1-2 years)

– Thereafter phlebotomies are performed at appropriate intervals to maintain ferritin levels between 50-100 tg/L (usually one phlebotomy every 3 months)

  • Chelating agents (such as Desferoxamine) are alternative agents and indicated when anemia and hypoproteinemia are severe enough to preclude phlebotomy

Treatment of Haematochromatosis

Phlebotomy is the treatment of choice in Hematochromatosis

Therapy of Haematochromatosis involves removal of excessive body iron and supportive treatment of damaged organs

Alcohol consumption should he eleminatedQ as increases ruck hematochronhth,sLs ten /oh/ Arthropathv,

Hypogonadism, Diabetes and Bronzing (pigmentation) of skin are all characteristic manifestation of hematochromatosis

Note: The combination of skin hyperpigmentation and insulin deficiency (diabetes) is called Bronze diabetes.

The characterstic  clinical features of Haemoehromatosis in order frequency areQ :

  • Hepatomegaly (95%1
  • Skin pigmentation (90%)
  • Diabetes mellitus (65%)
  • Arthropathy (25-50%)
  • Cardiac disease (15%)
  • Hypogonadism

Quiz In Between


Q. 7

Which of the following statements about Hemochromatosis is true:

 A

Shows complete penetrance

 B

Inherited as an autosomal recessive disorder

 C

Phlebotomy is curative

 D

More common in Females

Q. 7

Which of the following statements about Hemochromatosis is true:

 A

Shows complete penetrance

 B

Inherited as an autosomal recessive disorder

 C

Phlebotomy is curative

 D

More common in Females

Ans. B

Explanation:

Answer is B (Inherited as an Autosomal Recessive) :

Hereditary Hemochromatosis is essentially inherited us an autosomal recessive condition.

Hereditary Hemochromatosis is essentially an Autosomal Recessive condition

The most common form of hereditary hemochromatosis is related to mutations in HFE gene, which is a gene located on the short arm of chromosome 6 and is FILA linked

HFE related hereditary hemochromatosis (most common type) is inherited as an autosomal recessive condition

Hereditary Hemochromatosis shows incomplete penetrance

Incomplete penetrance refers to the lack of disease symptoms in an individual despite the presence of pathological gene mutation

Expression of Hemochromatosis is variable and many HFE positive people neither have nor develop disease, thus displaying the phenomenon of incomplete penetrance

This suggests that other genetic and / or environmental factors modify the pathogenesis of disease Hereditary Hemochromatosis is more common in Men

The clinical expression of disease is 5 –10 times more common in men than women – Harrison Phlebotomy is an effective management option but it does not lead to cure

The therapy of hemochromatosis involves removal of excess body iron which is best accomplished by phlebotomy Phlebotomy is not curative and will be required at appropriate intervals to maintain.ferritin levels (usually one phlebotomy every 3 months)’ – Harrison


Q. 8

What accumulates in tissues in hemochromatosis‑

 A

Iron

 B

Copper

 C

Ceruloplasmin

 D

Lipofuschhin

Q. 8

What accumulates in tissues in hemochromatosis‑

 A

Iron

 B

Copper

 C

Ceruloplasmin

 D

Lipofuschhin

Ans. A

Explanation:

Ans. is ‘a’ i.e., Iron

  • Hemochromatosis is characterized by the excessive accumulation of body iron, most of which is deposited in parenchymal organs such as liver and pancreas.
  • Hemochromatosis is a disorder of iron metabolism.
  • Characterized by a triad of :-
  • Micronodular cirrhosis
  1. Diabetes mellitus
  2. Skin pigmentation
  • Organ not showing iron deposition in hemochromatosis
  1. Testis

Q. 9

In hemochromatosis iron not deposited in ‑

 A

Heart

 B

Pituitary

 C

Testis

 D

Skin

Q. 9

In hemochromatosis iron not deposited in ‑

 A

Heart

 B

Pituitary

 C

Testis

 D

Skin

Ans. C

Explanation:

Ans. is ‘c’ i.e., Testis

In hemochromatosis, hypogonadism is caused by impairment of hypothalamic pituitary function and not due to deposition of Iron in the Testis.

Hemochromatosis

  • Hemochromatosis is characterized by the excessive accumulation of body iron, most of which is deposited in parenchymal organs such as liver and pancreas.
  • The total body content of the iron is tightly regulated, as the daily losses are matched by gastrointestinal absorption. In hereditary hemochromatosis, regulation of intestinal absorption of dietary iron is lost, leading to net iron accumulation of 0.5 to 1.0 gm/year.
  • It may be recalled that the total body iron pool ranges from 2-6 gm in normal adults; about 0.5 gm is stored in the liver 98% of which is hepatocytes. In hemochromatosis the iron accumulation may exceed 50 gm, over one third of which accumulates in the liver.
  • The iron accumulation is life long, the rate of net iron accumulation is 0.5 to 1.0 gm/year. The disease manifests itself typically after 20 gm of storage iron have accumulated. The disease first mainfests itself in the fifth to sixth decades of life.
  • Excessive iron is directly toxic to host tissues
  • The clinical features of hemochromatosis are characterized principally by deposition of excess iron in the following organs in decreasing order of severity.

Quiz In Between



Iron Deficiency

Iron Deficiency

Q. 1

Best test to detect iron deficiency in community is –

 A

Transferrin

 B

Serum ferritin 

 C

Serum iron

 D

Hemoglobin

Q. 1

Best test to detect iron deficiency in community is –

 A

Transferrin

 B

Serum ferritin 

 C

Serum iron

 D

Hemoglobin

Ans. B

Explanation:

Ans. is ‘b’ i.e., Serum ferritin

“The single most sensitive tool for evaluating the iron status is by measurement of serum jerritin” – Park

“It is the most usefill indicator of iron status in a population where the Prevalence” of iron deficiency is not high.


Q. 2

Anemia of Chronic disease can be differentiated from Iron deficiency anemia by:

 A

↑ TIBC

 B

↓ TIBC

 C

↑ S.ferritn

 D

b and c

Q. 2

Anemia of Chronic disease can be differentiated from Iron deficiency anemia by:

 A

↑ TIBC

 B

↓ TIBC

 C

↑ S.ferritn

 D

b and c

Ans. D

Explanation:

Answer is B &  C  (↓TIBC;↑Ferritin)

Anemia of chronic disease is associated with decreased TIBC and increased serum Ferritin while Iron deficiency anemia is associated with Increased TIBC and reduced serum Ferritin

Differential diagnosis of Microcytic Hypochromic Anemia

 

Parameters

Iron deficiency

Chronic Inflammatory

Smear

Microcytic hypochromic + target cell

Normocytic Normochromic

> Microcytic Hypochromic

Se Fe

< 30 (4)

4(<50) 50)

TIBC

> 360 (i)

i (< 300)

Saturation

< 10 (4)

4- ( l 0-20)

Ferritin

< 15 (1-)

T (30-200)

Free Erythrocyte

Protporphrin

ted

ted


Q. 3

Iron deficiency anemia is seen with all of the following except:

September 2008

 A

Chronic blood loss

 B

Achlorhydria

 C

Extensive surgical removal of the proximal small bowel

 D

Excess of meat in the diet

Q. 3

Iron deficiency anemia is seen with all of the following except:

September 2008

 A

Chronic blood loss

 B

Achlorhydria

 C

Extensive surgical removal of the proximal small bowel

 D

Excess of meat in the diet

Ans. D

Explanation:

Ans. D: Excess of meat in the diet

Causes of iron deficiency anemia:

  • Diet

– The prevalence of iron deficiency anemia is low in geographic areas where meat is an important constituent of the diet.

Substances that diminish the absorption of ferrous and ferric iron are phytates, oxalates, phosphates, carbonates, and tannates. Ascorbic acid increases the absorption of ferric and ferrous iron.

  • Hemorrhage

–  Bleeding for any reason produces iron depletion. If sufficient blood loss occurs chronically, iron deficiency anemia ensues.

  • Malabsorption of iron

– Prolonged achlorhydria may produce iron deficiency because acidic conditions are required to release ferric iron from food.

– Extensive surgical removal of the proximal small bowel or chronic diseases, such as untreated sprue or celiac syndrome, can diminish iron absorption.

  • Increased demand: pregnancy, lactation and growth periods.

Quiz In Between


Q. 4

Which of the following is the first symptom of iron deficiency anemia?   

September 2010

 A

Low iron concentration in blood

 B

Reduced hemoglobin

 C

Reduced PCV

 D

Reduced ferritin

Q. 4

Which of the following is the first symptom of iron deficiency anemia?   

September 2010

 A

Low iron concentration in blood

 B

Reduced hemoglobin

 C

Reduced PCV

 D

Reduced ferritin

Ans. D

Explanation:

Ans. D: Reduced ferritin


Q. 5

Iron Deficiency anemia is commonly caused by:

September 2005, March 2009

 A

Enterobius vermicularis

 B

Taenia solium

 C

Ancylostoma duodenale

 D

All of the above

Q. 5

Iron Deficiency anemia is commonly caused by:

September 2005, March 2009

 A

Enterobius vermicularis

 B

Taenia solium

 C

Ancylostoma duodenale

 D

All of the above

Ans. C

Explanation:

Ans. C: Ancylostoma duodenale

An adult Ancylostome (hookworm) can suck about 0.2 ml blood a day, while the smaller necator sucks in about 0.03 ml per day. These worms frequently leave one site and attach themselves to other site. As the secretions of the worm contain anticoagulant activity, bleeding from the site may continue for several days adding to the blood loss.

This chronic blood loss over a period of time leads to a microcytic hypochromic anemia. Pinworm (Enterobius vermicularis) causes irritation and pruritis in the perianal and perineal area. It may cause symptoms of chronic salpingitis and appendicitis.

Taenia solium causes cysticercus cellulosae commonly in the subcutaneous tissues and muscles. It may also affect eye, brain, heart, lung or liver.


Q. 6

Pattern in peripheral smear in iron deficiency anemia ‑

 A

Normocytic normochromic

 B

Hypochromic normocytic

 C

Hypochromic microcytic

 D

Normochromic microcytic

Q. 6

Pattern in peripheral smear in iron deficiency anemia ‑

 A

Normocytic normochromic

 B

Hypochromic normocytic

 C

Hypochromic microcytic

 D

Normochromic microcytic

Ans. C

Explanation:

Ans. is ‘c’ i.e., Hypochromic microcytic

Quiz In Between


Q. 7

Following is true about iron dextran except ‑

 A

It is parenteral iron preparation

 B

It can be given either iv or im

 C

It binds to transferrin

 D

It is not excreted

Q. 7

Following is true about iron dextran except ‑

 A

It is parenteral iron preparation

 B

It can be given either iv or im

 C

It binds to transferrin

 D

It is not excreted

Ans. C

Explanation:

Ans. is ‘c’ i.e., It binds to trnasferrin


Q. 8

The iron preparation that can be given intravenously is ‑

 A

Ferrous sulphate

 B

Iron dextran

 C

Iron sorbitol citric acid complex

 D

Colloidal ferric hydroxide

Q. 8

The iron preparation that can be given intravenously is ‑

 A

Ferrous sulphate

 B

Iron dextran

 C

Iron sorbitol citric acid complex

 D

Colloidal ferric hydroxide

Ans. B

Explanation:

Ans. is ‘b’ i.e., Iron dextran


Q. 9

Which of the following statements about iron deficiency anemia is correct

 A

Decreased TIBC

 B

Increased ferritin levels

 C

Bone marrow iron is decreased after serum iron is decreased

 D

Bone marrow iron is decreased earlier than serum iron

Q. 9

Which of the following statements about iron deficiency anemia is correct

 A

Decreased TIBC

 B

Increased ferritin levels

 C

Bone marrow iron is decreased after serum iron is decreased

 D

Bone marrow iron is decreased earlier than serum iron

Ans. D

Explanation:

Ans. is ‘D’ i.e., Bone marrow iron is decreased earlier than serum iron

In iron deficiency anemia the first change is decrease in iron stores “

The decrease in iron stores is demonstrated by decreased serum ferritin level.

Remember,

Serum ferritin reflects the amount of storage iron in the body.

As the total body iron level begins to fall a characteristic, sequence of events ensue :

  • First Stage or Prelatent Stage of Iron Depletion
  • When iron loss exceeds absorption, a negative iron balance exists.
  • Stored iron begins to be, mobilized from stores. The iron present in the macrophages of liver, spleen and bone marrow are depleted
  • Decrease in stored iron is reflected by decrease in serum ferritin.
  • At this stage all other parameters of iron status are normal.

Second Stage or Stage of Latent Iron Deficiency :

  • Iron stores are exhausted but the blood hemoglobin level remains higher than the lower limit of normal. o After the exhaustion of iron stores :
  • The plasma iron concentration fallsQ.
  • Plasma iron binding capacity increases2.
  • Percentage saturation falls below 15%Q.
  • The percentage of sideroblast decreases in the bone marrowQ.

Third Stage or Stage of Apparent Iron Deficiency Anemia

  • Supply of iron to marrow becomes inadequate for normal hemoglobin production,
  • So the blood hemoglobin concentration fallsQ below the lower limit of normal and iron deficiency anemia is apparent.

Q. 10

Iron deficiency causes ‑

 A

Megaloblastic anemia

 B

Microcytic hypochromic anemia

 C

Macrocytic hypochromic anemia

 D

Microcytic hypochromic anemia

Q. 10

Iron deficiency causes ‑

 A

Megaloblastic anemia

 B

Microcytic hypochromic anemia

 C

Macrocytic hypochromic anemia

 D

Microcytic hypochromic anemia

Ans. B

Explanation:

Ans. is ‘b’ i.e., Microcytic hypochromic anemia 

Quiz In Between



Structure Of Rna

STRUCTURE OF RNA

Q. 1

All of the following statements about Ribozymes are false, EXCEPT:

 A

They are DNA molecules

 B

They are not present in ribosomes

 C

They plays a key role in RNA synthesis

 D

They play a key role in post-transcriptional conversion of pre-mRNA to mature mRNA

Q. 1

All of the following statements about Ribozymes are false, EXCEPT:

 A

They are DNA molecules

 B

They are not present in ribosomes

 C

They plays a key role in RNA synthesis

 D

They play a key role in post-transcriptional conversion of pre-mRNA to mature mRNA

Ans. D

Explanation:

Ribozymes are RNAs which exhibit highly substrate specific catalytic activity.
They play a key role in the intron transcripts excision and exon transcripts splicing events essential for the conversion of pre mRNA to mature mRNA.
 
Ribozymes catalyzed transesterification, and ultimate hydrolysis of phosphodiester bonds in RNA molecules. 
 
Ref: Textbook Of Medical Biochemistry (3Rd Edn.) By S. Ramakrishnan page 338.

Q. 2

mRNA is a complimentary copy of ‑

 A

TRNA

 B

RRNA

 C

Ribosomal DNA

 D

A single strand of DNA

Q. 2

mRNA is a complimentary copy of ‑

 A

TRNA

 B

RRNA

 C

Ribosomal DNA

 D

A single strand of DNA

Ans. D

Explanation:

D i.e. A single strand of DNA


Q. 3

True about ribozymes are A/E

 A

Catalytic activity

 B

Involved in transesterification

 C

Hammerhead metallo enzyme

 D

Deamination

Q. 3

True about ribozymes are A/E

 A

Catalytic activity

 B

Involved in transesterification

 C

Hammerhead metallo enzyme

 D

Deamination

Ans. D

Explanation:

D i.e. Deamination

Ribozyme is RNA with catalytic activityQ. Examples include selfsplicing group I introns, RNase P, & hammerhead metallo enzymeQ of virusoids (requiring Mg2+). These are involved in transesterification, phosphodiester bond hydrolysis (cleavage), RNA metabolism (splicing & endoribonuclease), peptide bond formation (peptidyl transferases) and site specific RNA cleavage.

Quiz In Between


Q. 4

Shine-Dalgarno sequence in bacterial mRNA is near:

 A

AUG codon

 B

UAA codon

 C

UAG codon

 D

UGA codon

Q. 4

Shine-Dalgarno sequence in bacterial mRNA is near:

 A

AUG codon

 B

UAA codon

 C

UAG codon

 D

UGA codon

Ans. A

Explanation:

A i.e. AUG Codon


Q. 5

Ribozymes is/are :

 A

Splicing of heterogenous RNA (hnRNA) to form mRNA

 B

Splicing of polypeptide chain and mRNA

 C

Transcription of mRNA

 D

All

Q. 5

Ribozymes is/are :

 A

Splicing of heterogenous RNA (hnRNA) to form mRNA

 B

Splicing of polypeptide chain and mRNA

 C

Transcription of mRNA

 D

All

Ans. A

Explanation:

Q. 6

Poly ‘A’ tail attached at 3′ end of mRNA helps in‑

 A

Unwinding of mRNA

 B

Stabilization of mRNA

 C

Polymerization of mRNA

 D

Transcription of mRNA

Q. 6

Poly ‘A’ tail attached at 3′ end of mRNA helps in‑

 A

Unwinding of mRNA

 B

Stabilization of mRNA

 C

Polymerization of mRNA

 D

Transcription of mRNA

Ans. B

Explanation:

Ans. is ‘b’ i.e., Stabilization of mRNA

At the 51-end, mRNA possesses a 7-methylguanosine triphosphate cap which helps in the recognition of mRNA in protein biosynthesis and it helps to stabilize the mRNA by preventing attack of 51-exonuclease.

At its 31-end, there is a poly-A tail made up of several adenylate residues which stabilize mRNA by preventing attack of 31-exonuclease.

Quiz In Between


Q. 7

3′ end of t-RNA posseses ‑

 A

Poly ‘A’ tail

 B

CCA sequence

 C

Anticodon

 D

D arm

Q. 7

3′ end of t-RNA posseses ‑

 A

Poly ‘A’ tail

 B

CCA sequence

 C

Anticodon

 D

D arm

Ans. B

Explanation:

 

t-RNA molecule get folded into a structure that appears like a clover leaf.

There are four arms.

  1. Acceptor arm : It consists of a base paired stem that terminates in the sequence CCA at the 3′ end. This is the attachment site for amino acids.
  2. D arm – It contains the base dihydrouridine (D).
  3.  Anticodon arm – It contains anticodon that base pairs with the codon of coming mRNA. Anticodon has nucleotide sequence complementary to the codon of mRNA and is responsible for the specificity of the t RNA.
  4. Tyr C arm : It contains both ribothymidine (T) and pseudouridine

Q. 8

True about tRNA ‑

 A

80% of total RNA

 B

Contains 50-60 nucleotides

 C

CCA sequence is transcribed

 D

Longest RNA

Q. 8

True about tRNA ‑

 A

80% of total RNA

 B

Contains 50-60 nucleotides

 C

CCA sequence is transcribed

 D

Longest RNA

Ans. C

Explanation:

 

“The CCA tail is a CCA sequence at 3′ end of the tRNA molecule. In prokaryotes, CCA sequence is transcribed. In eukaryotes, the CCA sequence is added during processing”.

“tRNA is the smallest of three major species of RNAs”   — Dinesh puri

tRNA comprises 15% of total RNA in the cell. It contains 73-93 nucleotide residue.


Q. 9

Both DNA and RNA are present in:

 A

Bacteria

 B

Prions

 C

Virioids

 D

Plasmid

Q. 9

Both DNA and RNA are present in:

 A

Bacteria

 B

Prions

 C

Virioids

 D

Plasmid

Ans. A

Explanation:

Ans. a. Bacteria

Both DNA and RNA are pre sent in Bacteria

Micro-organism Genetic Material
Bacteria Contain both DNA and RNA, as well as extra-chromosomal DNA material (plasmids)Q
Plasmid

Extra-choromosomal circular DNA present in cytoplasm of bacteria and capable of autonomous

Viroids Contain low molecular weight RNA (No DNA)Q
Prions

Are misfolded proteinsQ

Devoid of both DNA and RNA

 

Quiz In Between


Q. 10

Synthesis of rRNA takes place in

 A

Cytosol

 B

Nucleus

 C

Nucleolus

 D

Mitochondria

Q. 10

Synthesis of rRNA takes place in

 A

Cytosol

 B

Nucleus

 C

Nucleolus

 D

Mitochondria

Ans. C

Explanation:

Ans. is ‘c i.e., Nucleolus 

Organelle

Function

Nucleolus Site of synthesis of r-RNA
Ribosomes

Site of protein synthesis, translation of mRNA

RER / Site of protein synthesis
Granular ER

(e.g. hormones, proteins found in enzyme)

SER / Agrannlar

Site of steroid synthesis I0

ER detoxification / FA elongation

Golgi Body

Processing / packaging, intracellular sorting of proteins, formation of lysosomes
Lysosomes Contain digestive / lytic enzymes and hydrolases (suicidal bags of cell)
Peroxisomes

Contain oxidases


Q. 11

RNA which contains codon for speicific amino acid ‑

 A

tRNA

 B

rRNA

 C

mRNA

 D

None

Q. 11

RNA which contains codon for speicific amino acid ‑

 A

tRNA

 B

rRNA

 C

mRNA

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., m RNA

The m RNA carries genetic information in the form of codons.

  • Codons are a group of three adjacent nucleotides that code for the amino acids of protein.
  • Each mRNA molecule is a transcript of antisense or template strand of a particular gene.
  • Its nucleotide sequence is complementary to that of antisense or template strand of the gene, i.e. adenine for thyamine, guanine for cytosine, uracil for adenine (as RNA does not contain thymine) and cytosine for guanine.
  • For example, if antisense strand of DNA has a gene with sequence 5′-TTACGTAC-3′, its complementary RNA transcript will be 5 ‘-GUACGUAA-3’.

Q. 12

RNA is present in ‑

 A

Cytoplasm

 B

Nucleus

 C

Ribosome

 D

All of the above

Q. 12

RNA is present in ‑

 A

Cytoplasm

 B

Nucleus

 C

Ribosome

 D

All of the above

Ans. D

Explanation:

Ans. is `d’ i.e., All of the above

  • mRNA is synthesized from DNA by the process of transcription in the nucleus. 
  • After formation mRNA transport out of the nucleus into cytoplasm.
  • t-RNA is also synthesized in nucleus and is transported to cytoplasm.
  • Protein synthesis (translation) occurs in ribosomes, and requires both mRNA and tRNA.
  • rRNA is present in ribosomes.
  • rRNA is synthesized in nucleolus

Thus, RNA can be found in –

  1. Nucleus
  2. Cytoplasm
  3. Ribosome
  4. Nucleolus

Quiz In Between



Regulation & Factors of Heme Synthesis

Regulators & Factors of Heme Synthesis

Q. 1

Lead inhibits which enzymes in the heme synthesis pathway:           

CMC (Vellore) 07

 A

Aminolevulinate synthase

 B

Ferrochelatase and 6-ALA dehydratase

 C

Porphobilinogen deaminase

 D

Uroporphyrinogen decarboxylase

Q. 1

Lead inhibits which enzymes in the heme synthesis pathway:           

CMC (Vellore) 07

 A

Aminolevulinate synthase

 B

Ferrochelatase and 6-ALA dehydratase

 C

Porphobilinogen deaminase

 D

Uroporphyrinogen decarboxylase

Ans. B

Explanation:

Ans. Ferrochelatase and 6-ALA dehydratase


Q. 2

Rate limiting step in heme synthesis is catalyzed by ‑

 A

ALA dehydratase

 B

ALA synthase

 C

UPG decarboxylase

 D

Ferrochelatase

Q. 2

Rate limiting step in heme synthesis is catalyzed by ‑

 A

ALA dehydratase

 B

ALA synthase

 C

UPG decarboxylase

 D

Ferrochelatase

Ans. B

Explanation:

Ans. is ‘b’ i.e., ALA synthase

Quiz In Between



Alkaptonuria

Alkaptonuria

Q. 1

Alkaptonuria is caused by defect in which of the following enzymes?

 A

Enolase

 B

Homogentisate oxidase

 C

Pyruvate carboxylase

 D

None of the above

Q. 1

Alkaptonuria is caused by defect in which of the following enzymes?

 A

Enolase

 B

Homogentisate oxidase

 C

Pyruvate carboxylase

 D

None of the above

Ans. B

Explanation:

Alkaptonuria was first recognized and described in the 16th century.
Characterized in 1859, it provided the basis for Garrod’s classic ideas concerning heritable metabolic disorders.
The defect is lack of homogentisate oxidase. The urine darkens on exposure to air due to oxidation of excreted homogentisate.
Late in the disease, there is arthritis and connective tissue pigmentation (ochronosis) due to oxidation of homogentisate to benzoquinone acetate, which polymerizes and binds to connective tissue.
Ref: Harper 28th edition, chapter 29.

 


Q. 2

In alkaptonuria there is increased pigmentation in all of the following locations, EXCEPT: –

 A

Eyes

 B

Nose

 C

Ear

 D

Articular cartilage

Q. 2

In alkaptonuria there is increased pigmentation in all of the following locations, EXCEPT: –

 A

Eyes

 B

Nose

 C

Ear

 D

Articular cartilage

Ans. B

Explanation:

Alkaptonuria is an autosomal recessively inherited deficiency of homogentisic acid oxidase enzyme which is involved in the metabolism of phenylalanine and tyrosine. Due to this defect, an oxidation product gets deposited in the cartilage throughout the body. In these patients examination of the skin shows a slight darkish blue color below the skin in areas overlying cartilage such as in the ears, sclera, conjunctiva and cornea. Metabolites also get deposited in the heart valves leading aortic or mitral stenosis. 

 
Patients often develop back pain due to spondylitis. It can be differentiated from ankylosing spondylitis by the absence of fusion of sacroiliac joint.  Diagnosis can be made when urine turns black spontaneously when exposed to air due to the presence of homogentisic acid. 
 
REf: CURRENT Medical Diagnosis & Treatment 2014 chapter 40.

Quiz In Between



Metabolism of Aromatic Amino Acids

Metabolism of Aromatic Amino Acids

Q. 1

Which of the following is a primary ketone body that is formed from leucine, lysine, phenylalanine and tyrosine?

 A

Acetoacetate

 B

Acetone

 C

Beta hydroxy butyrate

 D

All of the above

Q. 1

Which of the following is a primary ketone body that is formed from leucine, lysine, phenylalanine and tyrosine?

 A

Acetoacetate

 B

Acetone

 C

Beta hydroxy butyrate

 D

All of the above

Ans. A

Explanation:

Acetoacetate is a primary ketone body. Beta hydroxy butyrate and acetone are secondary ketone bodies. Acetoacetate can be formed from acetyl CoA, it can also be formed by the degradation of carbon skeleton of ketogenic amino acids like leucine, lysine, phenylalanine and tyrosine.

Acetone is formed by the degradation of carbon skeleton of acetoacetate. Beta hydroxy butyrate is formed by the reduction of acetoacetate
 
Ref: Textbook of Biochemistry By D M Vasudevan, 3rd Edition, Page 131

 


Q. 2

Which of the following is caused by defective tyrosine metabolism?

 A

Richner-Hanhart syndrome

 B

Neonatal tyrosinemia

 C

Alkaptonuria

 D

All of the above

Q. 2

Which of the following is caused by defective tyrosine metabolism?

 A

Richner-Hanhart syndrome

 B

Neonatal tyrosinemia

 C

Alkaptonuria

 D

All of the above

Ans. D

Explanation:

Metabolic diseases of tyrosine catabolism include tyrosinosis, Richner-Hanhart syndrome, neonatal tyrosinemia, and alkaptonuria.
 
Ref: Harper 28th edition, chapter 29.

 


Q. 3

Which of the following is not synthesised from tyrosine?

 A

Norepinephrine

 B

Melatonin

 C

Thyroxine

 D

Dopamine

Q. 3

Which of the following is not synthesised from tyrosine?

 A

Norepinephrine

 B

Melatonin

 C

Thyroxine

 D

Dopamine

Ans. B

Explanation:

Quiz In Between


Q. 4

Precursor of tyrosine is:  

 A

Cysteine

 B

Histidine

 C

Tryptophan

 D

Phenylalanine

Q. 4

Precursor of tyrosine is:  

 A

Cysteine

 B

Histidine

 C

Tryptophan

 D

Phenylalanine

Ans. D

Explanation:

 

Amino acids and products

  • Cysteine forms glutathione, taurine etc.
  • Histidine forms histamine
  • Tryptophan forms serotonin, melatonin etc.
  • Under normal circumstances, the degradation of phenylalanine mostly occurs through tyrosine. Phenylalanine is hydroxylated at para-position by phenylalanine hydroxylase to produce tyrosine (p-hydroxy phenylalanine)

Q. 5

Melanin is synthesized from:        

 A

Tryptophan

 B

Tyrosine

 C

Methionine

 D

Taurine

Q. 5

Melanin is synthesized from:        

 A

Tryptophan

 B

Tyrosine

 C

Methionine

 D

Taurine

Ans. B

Explanation:

Q. 6

Tyrosine becomes essential in which of the following condition:          

 A

Wilsons disease

 B

Alkaptonuria

 C

Thyrosinosis

 D

Phenylketonuria

Q. 6

Tyrosine becomes essential in which of the following condition:          

 A

Wilsons disease

 B

Alkaptonuria

 C

Thyrosinosis

 D

Phenylketonuria

Ans. D

Explanation:

 

The amino acids arginine, cysteine, glycine, glutamine, histidine, proline, serine and tyrosine are considered conditionally essential, meaning they are not normally required in the diet, but must be supplied exogenously to specific populations that do not synthesize it in adequate amounts.

Individuals living with PKU must keep their intake of phenylalanine extremely low to prevent mental retardation and other metabolic complications.

However, phenylalanine is the precursor for tyrosine synthesis.

Without phenylalanine, tyrosine cannot be made and so tyrosine becomes essential in the diet of PKU patients.

Quiz In Between


Q. 7

Tyrosine enters gluconeogenesis by forming which substrate

 A

Succinyl CoA

 B

oc-ketoglutarate

 C

Fumarate

 D

Citrate

Q. 7

Tyrosine enters gluconeogenesis by forming which substrate

 A

Succinyl CoA

 B

oc-ketoglutarate

 C

Fumarate

 D

Citrate

Ans. C

Explanation:

 

  • TCA cycle intermediates are substrate for gluconeogenesis.
  • Gluconeogenic amino acids enter TCA cycle after their transamination into various intermediates of TCA cycle :‑

a)     Histidine, proline, glutamine and arginine are converted to glutamate which is then transaminated to a­ketoglutarate.

b)       Isoleucine, methionine and valine enter by conversion into succinyl CoA. Propionate (a short chain fatty acid) also enter at this level.

c)     Tyrosine, and phenylalanine enter by conversion into fumarate.

d)     Tryptophan is converted to alanine which is then transaminated to pyruvate.

e)     Hydroxyproline, serine, cysteine, threonine and glycine enter by conversion into pyruvate.


Q. 8

Tyrosine kinase receptor is activated by ‑

 A

Growth hormone

 B

Insulin

 C

TSH

 D

Glucagon

Q. 8

Tyrosine kinase receptor is activated by ‑

 A

Growth hormone

 B

Insulin

 C

TSH

 D

Glucagon

Ans. B

Explanation:

Ans. is ‘b’ i.e., Insulin


Q. 9

Which of the following is derived from tyrosine ‑

 A

Melatonin

 B

Serotonin

 C

Melanin

 D

Niacin

Q. 9

Which of the following is derived from tyrosine ‑

 A

Melatonin

 B

Serotonin

 C

Melanin

 D

Niacin

Ans. C

Explanation:

Ans. is ‘c’ i.e., Melanin

Tyrosine is a precursor of many important compounds such as catecholamines (epinephrine, norepinephrine ), dopamine), thyroxine, triiodothryonine, melanin.

Quiz In Between


Q. 10

Tyrosine utilized in synthesis of all except ‑

 A

Melanin

 B

Melatonin

 C

Dopamine

 D

Thyroxine

Q. 10

Tyrosine utilized in synthesis of all except ‑

 A

Melanin

 B

Melatonin

 C

Dopamine

 D

Thyroxine

Ans. B

Explanation:

Q. 11

Enzyme deficient in tyrosinemia type 1 ‑

 A

Phenylalanine hydroxylase

 B

Tyrosinase

 C

Fumarylacetoacetate hydroxylase

 D

Tyrosine transaminase

Q. 11

Enzyme deficient in tyrosinemia type 1 ‑

 A

Phenylalanine hydroxylase

 B

Tyrosinase

 C

Fumarylacetoacetate hydroxylase

 D

Tyrosine transaminase

Ans. C

Explanation:

 

Tyrosinemia

It is a defect in metabolism of tyrosine. It may be of following types :-

  1. Tyrosinemia type-I (tyrosinosis/hepatorenal syndrome) :- It is due to defect in fumarylacetoacetate hydroxylase deficiency. Patients with chronic tyrosinosis are prone to develop cirrhosis and hepatic carcinoma. There is cabbage like odor in acute tyrosinosis.
  2. Tyrosinemia type – II (Richer-Hanhart syndrome) :- It is due to deficiency of tyrosine transaminase (tyrosine aminotrans-ferase).
  3. Neonatal tyrosinemia : – It is due to deficiency of hydroxyphenyl pyruvate hydroxylase.

Q. 12

Catecholamines are synthesized from

 A

Tryptophan

 B

Tyrosine

 C

Methionine

 D

Histidine

Q. 12

Catecholamines are synthesized from

 A

Tryptophan

 B

Tyrosine

 C

Methionine

 D

Histidine

Ans. B

Explanation:

Ans. is ‘b’ i.e., Tyrosine 

  • Catecholamines (epinephrine, norepinephrine and dopamine) are synthesized from tyrosin.
  • Has been explained in previous seesions.

Quiz In Between



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