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Vitamin B3- metabolism

Vitamin B3- metabolism

Q. 1

Niacin is required for growth of – Oxidase

 A

M. tuberculosis

 B

M. kansasii

 C

M. Scrofuloderma

 D

M. Avium

Q. 1

Niacin is required for growth of – Oxidase

 A

M. tuberculosis

 B

M. kansasii

 C

M. Scrofuloderma

 D

M. Avium

Ans. A

Explanation:

Ans. is ‘a’ i.e., M. tuberculosis 


Q. 2

One mg. of Niacin is produced by…………………….. mg. of Tryptophan-

 A

22

 B

37

 C

55

 D

60

Q. 2

One mg. of Niacin is produced by…………………….. mg. of Tryptophan-

 A

22

 B

37

 C

55

 D

60

Ans. D

Explanation:

Ans. is ‘d’ i.e., 60 

About 60 mg of tryptophan is required to result in I mg of niacin.


Q. 3

Niacin is synthesized from ‑

 A

Arginine

 B

Histidine

 C

Tryptophan

 D

Tyrosine

Q. 3

Niacin is synthesized from ‑

 A

Arginine

 B

Histidine

 C

Tryptophan

 D

Tyrosine

Ans. C

Explanation:

Q. 4

Niacin is derived from which amino acid?

 A

Tyrosine

 B

Phenylalanine

 C

Tryptophan

 D

Methionine

Q. 4

Niacin is derived from which amino acid?

 A

Tyrosine

 B

Phenylalanine

 C

Tryptophan

 D

Methionine

Ans. C

Explanation:

Quiz In Between



Vitamin B3- metabolism

Vitamin B3- metabolism


VITAMIN B3 (NIACIN)

  • Vitamin B3 is also called as Nicotinic acid or nicotinamide.
  • Niacin can be synthesized tryptophan (1mg of the niacin formed from 60mg of tryptophan)

Active form of niacin-

  1. NAD+ (Nicotinamide Adenine Dinucleotide)
  2. NADP+ (Nicotinamide Adenine Dinucleotide Phosphate)

Coenzymes involved in reactions-

  1. Oxidoreduction reaction-

i) NAD+ linked dehydrogenases-

  • Isocitrate dehydrogenase
  • Malate dehydrogenase
  • α-ketoglutarate dehydrogenase
  • glutamate dehydrogenase
  • glyceraldehydes-3- P dehydrogenase
  • lactate dehydrogenase
  • β-hydroxyl acyl CoA dehydrogenase

ii) NADP+ linked dehydrogenases-

  • Glucose-6-P dehydrogenase in HMP shunt pathway

 2. ADP ribosylation

Metabolism & Excretions-

  • Nicotinamide excreted in urine are N1 –methyl nicotinamide and N1 –methyl 2-pyridone 5-carboxamide (2-pyridine).
  • N-methyl nicotinamide metabolized to methylpyridone-2- and 4-carboxamide
  • Nicotinic acid conjugated with glycine to form nicotinuric acid
  • Nicotinic acid methylated to trignonelline.
  • Daily recommended dose – 20mg/day 

Exam Important

  1. Vitamin B3 is also called as Nicotinic acid or nicotinamide.
  2. Niacin can be synthesized tryptophan (1mg of the niacin formed from 60mg of tryptophan)

Coenzymes involved in reactions-

  1. Oxidoreduction reaction-

i) NAD+ linked dehydrogenases-

  • Isocitrate dehydrogenase
  • Malate dehydrogenase
  • α-ketoglutarate dehydrogenase
  • glutamate dehydrogenase
  • glyceraldehydes-3- P dehydrogenase
  • lactate dehydrogenase
  • β-hydroxyl acyl CoA dehydrogenase

ii) NADP+ linked dehydrogenases-

  • Glucose-6-P dehydrogenase in HMP shunt pathway
  • Nicotinamide excreted in urine are N1 –methyl nicotinamide and N1 –methyl 2-pyridone 5-carboxamide (2-pyridine).
  • N-methyl nicotinamide metabolized to methylpyridone-2- and 4-carboxamide
  • Nicotinic acid conjugated with glycine to form nicotinuric acid
  • Nicotinic acid methylated to trignonelline.
  • Daily recommended dose – 20mg/day
Don’t Forget to Solve all the previous Year Question asked on Vitamin B3- metabolism

Module Below Start Quiz

Vitamin B3 Deficiency

Vitamin B3 & Deficiency

Q. 1

Nicotinamide is preferred over Niacin because?

 A Flushing is seen with niacin
 B

Abdominal pain is seen with niacin

 C Breathlessness is seen with niacin
 D

Less bioavailability

Q. 1

Nicotinamide is preferred over Niacin because?

 A Flushing is seen with niacin
 B

Abdominal pain is seen with niacin

 C Breathlessness is seen with niacin
 D

Less bioavailability

Ans. A

Explanation:

Flushing is seen with niacin REF: Nutrition Almanac by John D. Kirschmann, Nutrition Search, Inc page 31

Niacin causes sudden release of histamine which produces certain s/e which are not seen with nicotinamide

  • Intense flushing
  • Tingling
  • Numbness
  • Throbbing headache due to cerebral vasodilation.

Q. 2

A 54-year-old man has a total cholesterol of 272 and LDL level of 210. His therapy is initiated with dietary modification and an exercise regimen, but he is unresponsive and so is prescribed nicotinic acid (Niacin). Which of the following symptoms will this patient likely experience from this drug?

 A

Bradycardia

 B

Facial flushing

 C

Hypoalbuminemia

 D

Hypoglycemia

Q. 2

A 54-year-old man has a total cholesterol of 272 and LDL level of 210. His therapy is initiated with dietary modification and an exercise regimen, but he is unresponsive and so is prescribed nicotinic acid (Niacin). Which of the following symptoms will this patient likely experience from this drug?

 A

Bradycardia

 B

Facial flushing

 C

Hypoalbuminemia

 D

Hypoglycemia

Ans. B

Explanation:

Niacin, or vitamin B3, is an agent that results in the following physiologic changes: LDL reductions tend to occur in 5-7 days with the maximal effect seen in 3-5 weeks; triglycerides and VLDL are reduced by 20% to 40% in 1-4 days; and HDL levels can increase by 20%.

This agent is indicated as adjunctive therapy in patients with elevated cholesterol and triglycerides when diet and other nondrug therapies are inadequate. 

The most common adverse effect of this agent is generalized flushing with a sensation of warmth, especially in the facial area.

This reaction may be so severe in some patients that they discontinue therapy.

Other common adverse effects include hepatotoxicity, tachycardia, hypoalbuminemia, hyperglycemia, nausea, vomiting, hyperuricemia, glucose intolerance, pruritus, peptic ulcer disease, and dry skin.


Q. 3

Maize contains the vitamin niacin. Pellagra is a disease that results from niacin deficiency.

Assertion: Consumption of maize may aggravate Pellagra.

Reason: Some strains of maize contains excess of Leucine which interferes in the conversion of Tryptophan into Niacin.

 A

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion

 B

Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion

 C

Assertion is true, but Reason is false

 D

Assertion is false, but Reason is true

Q. 3

Maize contains the vitamin niacin. Pellagra is a disease that results from niacin deficiency.

Assertion: Consumption of maize may aggravate Pellagra.

Reason: Some strains of maize contains excess of Leucine which interferes in the conversion of Tryptophan into Niacin.

 A

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion

 B

Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion

 C

Assertion is true, but Reason is false

 D

Assertion is false, but Reason is true

Ans. A

Explanation:

Pellagra is caused by Niacin deficiency and anything that interferes in the absorption or production of Niacin will aggravate the condition.

Ref: Park’s Textbook of Preventive Medicine, 17th Edition, Page 427.

Quiz In Between


Q. 4

A 10 year old child is suspected of having pellagra because of chronic symptoms including diarrhea, a red scaly rash, and mild cerebellar ataxia. However, his diet is not deficient in protein and he appears to be ingesting adequate amounts of niacin. A sister has a similar problem. Chemical analysis of his urine demonstrates large amounts of free amino acids. Which of the following is the most likely diagnosis?

 A

Alkaptonuria

 B

Carcinoid syndrome

 C

Ehlers-Danlos syndrome

 D

Hartnup’s disease

Q. 4

A 10 year old child is suspected of having pellagra because of chronic symptoms including diarrhea, a red scaly rash, and mild cerebellar ataxia. However, his diet is not deficient in protein and he appears to be ingesting adequate amounts of niacin. A sister has a similar problem. Chemical analysis of his urine demonstrates large amounts of free amino acids. Which of the following is the most likely diagnosis?

 A

Alkaptonuria

 B

Carcinoid syndrome

 C

Ehlers-Danlos syndrome

 D

Hartnup’s disease

Ans. D

Explanation:

The child has Hartnup’s disease.
This condition clinically resembles pellagra (“diarrhea, dementia, and dermatitis”), and may be misdiagnosed as this nutritional (niacin) deficiency. In fact, niacin therapy may actually be helpful in controlling the symptoms.
The underlying problem is a defect in the epithelial transport of neutral amino acids, including tryptophan, which can act as a precursor of niacin. The defective amino acid transport leads to poor absorption of dietary amino acids as well as excess amino acid secretion in the urine.
Alkaptonuria  is characterized by urine that turns black upon standing and a debilitating arthritis.
 
Carcinoid syndrome is seen in patients with carcinoid tumor. It is characterized by episodes of flushing, diarrhea, hypertension, and bronchoconstriction.
 
Ehlers-Danlos syndrome is a disease characterized by abnormal collagen formation leading to very elastic skin, joint problems, and fragility of some blood vessels and the intestines.
 
Ref: Bender D.A. (2011). Chapter 44. Micronutrients: Vitamins & Minerals. 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

In Niacin deficiency, all of the following are seen except:

 A

Deafness

 B

Diarrhea

 C

Dementia

 D

Dermatitis

Q. 5

In Niacin deficiency, all of the following are seen except:

 A

Deafness

 B

Diarrhea

 C

Dementia

 D

Dermatitis

Ans. A

Explanation:

Ans. is ‘a’ i.e., Deafness 

o Niacin deficiency results in ‘Pellagra’

Pellagra is identified by the presence of three ‘D’s —> Diarrhea, Dementia, Dermatitis


Q. 6

Niacin deficiency causes all except –

 A

Diarrhea

 B

Dyspepsia

 C

Dementia

 D

Dermatitis

Q. 6

Niacin deficiency causes all except –

 A

Diarrhea

 B

Dyspepsia

 C

Dementia

 D

Dermatitis

Ans. B

Explanation:

Ans. is ‘b’ i.e., Dyspepsia 

Quiz In Between


Q. 7

Niacin deficiency cause –

 A

Pellagra

 B

Scurvy

 C

Rickets

 D

Lathyrism

Q. 7

Niacin deficiency cause –

 A

Pellagra

 B

Scurvy

 C

Rickets

 D

Lathyrism

Ans. A

Explanation:

Ans. is ‘a’ i.e., Pellagra 


Q. 8

Niacin deficiency in a maize-eating population is due to-

 A

High Tryptophan 

 B

High lsoleucine

 C

High leucine

 D

High Phenylalanine

Q. 8

Niacin deficiency in a maize-eating population is due to-

 A

High Tryptophan 

 B

High lsoleucine

 C

High leucine

 D

High Phenylalanine

Ans. C

Explanation:

Ans. is ‘c’ i.e., High Leucine 

Excess of Leucine interferes in conversion of Tryptophan into Niacin, and aggravates the pallagrogenic action of inake.


Q. 9

Niacin deficiency causes ‑

 A

Pigmentation

 B

Diarrhea

 C

Rash

 D

Lactic acidosis

Q. 9

Niacin deficiency causes ‑

 A

Pigmentation

 B

Diarrhea

 C

Rash

 D

Lactic acidosis

Ans. B

Explanation:

Ans. is ‘b’ i.e., Diarrhea 

  • Deficiency of niacin (and tryptophan) causes pellagra which is characterized by 3 Ds, i.e. dermatitis, diarrhea and dementia.
  • Pellagra is common in people consuming maize and sorghum (jowar) as their staple foods.
  • These two are poor in niacin and tryptophan, and rich in leucin.
  • Excess of leucine inhibits the conversion of tryptophan into niacin.

Quiz In Between



Vitamin B3 Deficiency

Vitamin B3 Deficiency


Uses-

  • As lipid modifying drug
  • Reduces triglyceride and LDL-C levels

Vitamin B3 Deficiency-

Pellagra-

  • Caused due to niacin deficiency
  • Common in people consuming maize and sorghum (poor in niacin & tryptophan and rich in leucine)

Clinical Manifestations-

Characterized by 4Ds-

            Dermatitis, Diarrhea, Dementia and Death

  • Casal’s necklace– rash form around neck
  • Apathy
  • Depressive psychosis
  • Hartnup disease
  • Carcinoid syndrome

Vitamin B3 Toxcity-

  • Cutaneous flushing
  • Gastric irritation
  • Hepatic toxicity
  • Macular edema and cysts
  • Hyperuricemia
  • Glucose intolerance

Exam Important

Pellagra-

  • Caused due to niacin deficiency
  • Common in people consuming maize and sorghum (poor in niacin & tryptophan and rich in leucine)

Clinical Manifestations-

Characterized by 4Ds-

  • Dermatitis, Diarrhea, Dementia and Death
  •  Casal’s necklace– rash form around neck
Don’t Forget to Solve all the previous Year Question asked on Vitamin B3 Deficiency

Module Below Start Quiz

Lipoprotein Structure

Lipoprotein- structure

Q. 1 The major lipid of the lipoproteins is:
 A Oleic acid
 B Palmitic acid
 C Linoleic acid
 D Arachidonic acid
Q. 1 The major lipid of the lipoproteins is:
 A Oleic acid
 B Palmitic acid
 C Linoleic acid
 D Arachidonic acid
Ans. D

Explanation:

Arachidonic acid


Q. 2

Human plasma lipoprotein containing the highest percentage of triacylglycerol by weight is:

 A

VLDL

 B

Chylomicrons

 C

HDL

 D

LDL

Q. 2

Human plasma lipoprotein containing the highest percentage of triacylglycerol by weight is:

 A

VLDL

 B

Chylomicrons

 C

HDL

 D

LDL

Ans. B

Explanation:

Triacylglycerol or triglyceride is an ester that is derived from glycerol and three fatty acids. Chylomicrons are lipoproteins that are lowest in density and largest in size which contains the highest percentage of triacylglycerol and the smallest percentage of protein.

Besides containing 80 to 95 percent triglyceride, chylomicrons contain 2 to 7 percent cholesterol, 3 to 6 percent phospholipid, and 1-2 percent protein.
 
Ref: Lippincott’s Illustrated Reviews: Biochemistry, 3rd Edition, Page 225; Fitness and Health By Brian J. Sharkey, Steven E. Gaskill, 2007, Page 274.

Q. 3

. The human plasma lipoprotein containing the highest percentage of triacylglycerol by weight is:

 A

VLDL

 B

Chylomicrons

 C

HDL

 D

LDL

Q. 3

. The human plasma lipoprotein containing the highest percentage of triacylglycerol by weight is:

 A

VLDL

 B

Chylomicrons

 C

HDL

 D

LDL

Ans. B

Explanation:

B i.e. Chylomicrins

Lipoproteins may be differentiated on the basis of their lipid & protein compositions. The lipoproteins containing the largest percentage of triacylglycerol are Chylomicrons (90%).

Lipoprotein Structure



Glycolipids

Glycolipids

Q. 1 Glycerol  is  the  backbone  of  all  of  the following phospholipids EXCEPT
 A Phosphatidylethanolamine
 B Cardiolipin
 C Phosphatidylcholine
 D Sphingomyelin
Q. 1 Glycerol  is  the  backbone  of  all  of  the following phospholipids EXCEPT
 A Phosphatidylethanolamine
 B Cardiolipin
 C Phosphatidylcholine
 D Sphingomyelin
Ans. D

Explanation:

Sphingomyelin   = phosphorylcholine + ceramide

Ceramide            = fatty acid + sphingosine

Sphingosine        = condensing palmitic acid with a decarboxylated   serine   and   then   reducing   the product

Glycerol  never  is  involved  in  the  structure  of sphingomyelin. Phosphatidylethanolamine, cardiolipin, phosphatidylcholine, and phosphatidylinositol are synthesized using phosphatidic acid as the basic building block  Phosphatic acid  is  diacylglycerol with a phosphate  ester on carbon three; therefore, glycerol is the backbone of all of these compounds. FAQ Sphingomyelin :-

–  Membranous myelin sheath that surrounds nerve cell axons.

–    It is the only sphingolipid NOT derived from Glycerol.

–       Associated  with  increased  accumulation  in Niemann-Pick  Disease.


Q. 2

Which of the following occurs in the lipidosis known as Tay-Sachs disease?

 A

Synthesis of a specific ganglioside is excessive

 B

Xanthomas due to cholesterol deposition are observed

 C

Phosphoglycerides accumulate in the brain

 D

Ganglioside GM2 is not catabolized by lysosomal enzymes

Q. 2

Which of the following occurs in the lipidosis known as Tay-Sachs disease?

 A

Synthesis of a specific ganglioside is excessive

 B

Xanthomas due to cholesterol deposition are observed

 C

Phosphoglycerides accumulate in the brain

 D

Ganglioside GM2 is not catabolized by lysosomal enzymes

Ans. D

Explanation:

In the genetic disorder known as Tay-Sachs disease, ganglioside GM2 is not catabolized. As a consequence, the ganglioside concentration is elevated many times higher than normal. The functionally absent lysosomal enzyme is β-N- acetylhexosaminidase.

The elevated GM2 results in irreversible brain damage to infants, who usually die before the age of 3 years. Under normal conditions, this enzyme cleaves N- acetylgalactosamine from the oligosaccharide chain of this complex sphingolipid, allowing further catabolism to occur.

The cause of most lipidoses (lipid storage diseases) is similar.

That is, a defect in catabolism of gangliosides causes abnormal accumulation.

None of the other choices result in lipidotic disorders. 

Ref: Hopkin R., Grabowski G.A. (2012). Chapter 361. Lysosomal Storage Diseases. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison’s Principles of Internal Medicine, 18e.

 


Q. 3

Glycosphingolipidis made up of:

 A

Glucose

 B

Fatty acids

 C

Sphingosine

 D

All Correct

Q. 3

Glycosphingolipidis made up of:

 A

Glucose

 B

Fatty acids

 C

Sphingosine

 D

All Correct

Ans. D

Explanation:

A, B, C i.e. Glucose, Sphingosine, Fatty acids

Glycosphingolipid = Ceramide (Sphingosine / amino alcohol + Fatty acid) + Mono/oligo saccharide like glucose, galactose. Ganglioside (acidic glycosphingolipid) = Ceramide + Oligosaccharide + NANA (N-acetylneuraminic acid or sialic acid)

 

–  Glyco-sphingolipid is made up of ceramide (which is a long chain fatty acid attached to amino group of sphingosine through an amide linkage i.e. = sphingosine/ amino alcohol + Fatty acid) attached directly to mono /oligo saccharide

(polar head) by an 0-glycosidic bond. Glycosphingolipids differ from sphingomyelin (phospho- sphingolipid) in that they do not contain phosphate (polar group); and differ from glycerophospholipids (phosphoglycerides) that they do not contain glycerol.

Ganglioside (acidic, negatively charged glyco-sphingolipid) contain sphingosine alcohol (4 sphingenine) 1 molecule, long chan fatty acid (1 mol), Oligosaccharide polar head and 1 or more residues of N- acetylneurminic acid (Neu 5 Ac), a sialic acid (often simply called sialic acid) giving it a negative charge, at termini. Ganglioside do not contain glycerol and phosphateQ.

Ceramide containing sphingosine amino alcohol is present in all sphingolipids (ie. phospho & glyco- sphingolipids)Q.



Q. 4

Which of the following is not a glycerosphingolipid?

 A

Lecithin

 B

Cardiolipin

 C

Plasmalogens

 D

Sphingomyelin

Q. 4

Which of the following is not a glycerosphingolipid?

 A

Lecithin

 B

Cardiolipin

 C

Plasmalogens

 D

Sphingomyelin

Ans. D

Explanation:

 

Phospholipids are :

  1. Glycerophospholipids (glycerol containing) :- Phosphatidylcholine (lecithin), phosphatidylethanolamine (cephaline), phosphatidylserine, phosphatidylinositol, plasmalogens, lysophospholipids, cardiolipin.
  2. Sphingophospholipids (sphingosine containing) :- Sphingomyeline

Quiz In Between



Lipoprotein Structure

Lipoprotein Structure


LIPOPROTEINS

  • Free fatty acids (FAA) is metabolically most active of the plasma lipids.
  • Lipids are transported in the form of lipoproteins.
  • Non polar lipid contains cholesterol ester, cholesterol, phospholipid, triacylglycerol.
  • Protein part of lipoprotein is apolipoprotein.

Major lipoproteins according to density are-

  1. Chylomicrons- These are principal form in which dietary lipids (exogenous lipids) are carried from intestine to liver.
  2. Very low density lipoproteins (VLDL)
  3. Low density lipoproteins (LDL)- major source of cholesterol to peripheral tissues.
  4. Intermediate density lipoproteins (IDL)
  5. High density lipoproteins (HDL)

Separation of Lipoproteins-

  1. Electrophoresis-
  • Chylomicrons have no mobility and remains at orginial position
  • HDL has maximum mobility and move longest distance.

2. Ultracentrifugation-

  • Chylomicrons are largest with maximum lipid contents.

Exam Important

  • Free fatty acids (FAA) is metabolically most active of the plasma lipids.
  • Non polar lipid contains cholesterol ester, cholesterol, phospholipid, triacylglycerol.
  • Protein part of lipoprotein is apolipoprotein.
  • Chylomicrons- These are principal form in which dietary lipids (exogenous lipids) are carried from intestine to liver.
  • Low density lipoproteins (LDL)- major source of cholesterol to peripheral tissues.

Electrophoresis-

  • Chylomicrons have no mobility and remains at orginial position
  • HDL has maximum mobility and move longest distance.

Ultracentrifugation-

  • Chylomicrons are largest with maximum lipid contents.
Don’t Forget to Solve all the previous Year Question asked on Lipoprotein Structure

Module Below Start Quiz

Glycolipids

GLYCOLIPIDS


GLYCOLIPIDS (GLYCOSPHINGOLIPIDS)

  • Glycosphingolipid = Sphingosine + long chain fatty acid + sugars
  • Glycolipids are synthesized in endoplasmic reticulum.
  • Glycosphingolipids are 4 types-

Cerebrosides– ( ceramide + monosaccharides)

  • Cerebroside= sphingoside + long chain fatty acid + glucose
  • Monosaccharides used is mostly glucose (glucocerebroside) or galactose (galactocerebroside).
  • Clinical Aspect- 
  1. Krabbe’s disease caused by deficiency of enzyme of ?- galactosidase (Galactocerebroside accumulates in brain).
  2. Gaucher’s disease caused by deficiency of ?- glucosidase (glucocerebrosidase)
  • Glucocerebroside (glucosylceramide) is accumulated in brain.
  1. Sulfatides– cerebroside + sulphate
  2. Globosides– ceramide + oligosaccharide
  3. Gangliosides
  • ceramide + oligosaccharide chain (glucose+galactose) + N- acetylneuromic acid (NANA)
  • Gangliosides= Sphingosine+ long chain fatty acid + oligosaccharide chain (glucose or galactose)+ NANA
  • Clinical Aspect-
  • Tay- Sach’s Disease– caused due to deficiency of hexosaminidase (alpha subunit)
  • Sandoff disease- caused due to deficiency of hexoaminidase (Beta subunit)

Exam Important

  • Glycosphingolipid = Sphingosine + long chain fatty acid + sugars
  • Glycolipids are synthesized in endoplasmic reticulum.
  • Glycosphingolipids are 4 types-

Cerebrosides– ( ceramide + monosaccharides)

  • Cerebroside= sphingoside + long chain fatty acid + glucose
  • Monosaccharides used is mostly glucose (glucocerebroside) or galactose (galactocerebroside).
  • Clinical Aspect-
  1. Krabbe’s disease caused by deficiency of enzyme of ?- galactosidase.
  2. Galactocerebroside accumulates in brain.
  3. Gaucher’s disease caused by deficiency of ?- glucosidase (glucocerebrosidase)
  4. Glucocerebroside (glucosylceramide) is accumulated in brain.
  5. Sulfatides– cerebroside + sulphate
  6. Globosides– ceramide + oligosaccharide
  7. Gangliosides
  • ceramide + oligosaccharide chain (glucose+galactose) + N- acetylneuromic acid (NANA)
  • Gangliosides= Sphingosine+ long chain fatty acid + oligosaccharide chain (glucose or galactose)+ NANA
  • Tay- Sach’s Disease– caused due to deficiency of hexosaminidase (alpha subunit) .
Don’t Forget to Solve all the previous Year Question asked on GLYCOLIPIDS

Module Below Start Quiz

Isoenzymes

ISOENZYMES

Q. 1

True about isoenzymes is:

 A

Same quaternary structure

 B

Same distribution in different organs

 C

Same enzyme classification with same umbers

 D

Catalyze the same reaction

Q. 1

True about isoenzymes is:

 A

Same quaternary structure

 B

Same distribution in different organs

 C

Same enzyme classification with same umbers

 D

Catalyze the same reaction

Ans. D

Explanation:

    • Isoenzymes are the multiple forms of the same enzyme in a single species that catalyze the same chemical reaction or reactions, but differ from each other structurally, electrophoretically and immunologically.
    • Though the same chemical reaction is catalyzed, the different isoenzymes may catalyze the same reaction at different rates.
    • Isoenzymes have different pH optimes, Km and V max values.
    • Isoenzymes may differ in their amino acid sequence and their quarternary structures.
    • The isoenzymes may have different properties also for e.g. LDH-4 and LDH-5 are easily destroyed by heat, whereas LDH-1 and LDH-2 are not, if heated upto 60°C. (Heat resistant).
    • Individual isoenzymes (isozymes) are distinguished and numbered on the basis of electrophoretic mobility, with the number 1 being assigned to that form having the highest mobility toward the anode, for e.g. LDH-1 has the highest mobility towards the anode and LDH-5 is the slowest.
    • Isoenzymes have different tissue distributions. Therefore the pattern of isoenzymes found in the plasma may serve as a means of identifying the site of tissue damage. Example of the diagnostic use of isoenzymes are the study of Lactate Dehydrogenase and Creatine Kinase.

Q. 2

True about isoenzymes is/are:

 A

Different km value

 B

Act on different substrate

 C

Same electrophoretic mobility

 D

All

Q. 2

True about isoenzymes is/are:

 A

Different km value

 B

Act on different substrate

 C

Same electrophoretic mobility

 D

All

Ans. A

Explanation:

  • Isozymes are the physically distinct forms of the same enzymes that catalyze the same reaction, and differ from each other structurally, electrophoretically and immunologically.
  • They differ in their physical properties because of genetically determined difference in amino acid sequence.
  • They are separated by electrophoresis as they have different electrophoretic mobility.
  • They have different Km value.
  • Isoenzyme of an oligomeric enzyme process differ in combination of its peptide protomer.

Q. 3

Which isoenzyme of LDH is seen in heart

 A

LDH 1

 B

LDH 2

 C

LDH 3

 D

LDH 4

Q. 3

Which isoenzyme of LDH is seen in heart

 A

LDH 1

 B

LDH 2

 C

LDH 3

 D

LDH 4

Ans. A

Explanation:

Ans. is ‘a’ i.e., LDH1

Quiz In Between


Q. 4

First enzyme to be raised in MI is ‑

 A

CPK-MB

 B

LDH

 C

Myoglobin

 D

Troponin-I

Q. 4

First enzyme to be raised in MI is ‑

 A

CPK-MB

 B

LDH

 C

Myoglobin

 D

Troponin-I

Ans. C

Explanation:

Ans. is ‘c’ i.e., Myoglobin 


Q. 5

Enzyme specificity is given by ‑

 A

Km

 B

Vrm„

 C

Both

 D

None

Q. 5

Enzyme specificity is given by ‑

 A

Km

 B

Vrm„

 C

Both

 D

None

Ans. A

Explanation:

Ans. is ‘a’ i.e., K. 

  • The Km of an enzyme is the concentration of the substrate that enables the enzyme to function at half maximum activity and is therefore a measure of the specificity of a substrate.for the enzyme” Clinical biochemistry
  • Actually enzyme specificity is not measured by Km alone.
  • It is measured by the ratio Kcat/Km which is a second order rate constant for the reaction between substrate and free enzyme.
  • This ratio is important, for it provides a direct measure of enzyme efficiency and specificity.
  • Note : Kcat is turnover number and measures the rate of the catalytic process.

Q. 6

Q10 in enzyme matches with ‑

 A

2

 B

4

 C

8

 D

10

Q. 6

Q10 in enzyme matches with ‑

 A

2

 B

4

 C

8

 D

10

Ans. A

Explanation:

Ans. is ‘a’ i.e., 2

  • Most enzyme show a 50-300% (average 200%) increase in reaction rate when the temperature is increased by 10°, and the ratio of rate constant at two temperatures 10° apart is usually between 1.5 to 4 (average 2) for most enzymes.
  • This value is termed as Q10.
  • “The rate of enzymatic reaction doubles with every 10° rise in temperature. “

Q. 7

Fastest acting enzyme ‑

 A

LDH

 B

Trypsin

 C

Catalase

 D

None

Q. 7

Fastest acting enzyme ‑

 A

LDH

 B

Trypsin

 C

Catalase

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Catalase 

Measurement of enzyme activity

  • The activity of enzyme is measured in terms of the following :
  • Unit of enzyme activity : – By international agreement, one unit enzyme activity is defined as the amount causing transformation of 1.0 micro mole of substrate per minute at 25° C. It is usually expressed as mole of substrate disappeared or mole of product formed per minute.
  • Specific activity : – It refers to the number of enzyme units per milligram of protein. It is a measure of enzyme purity; higher the enzyme purity, more is the specific activity.
  • Turn over number : – This refers to the number of substrate molecules transformed per unit time by a single enzyme molecule (or by a single catalytic site), when the enzyme concentration alone is rate-limiting factor. Catalase has the highest turnover number and hence is the fastest active enzyme. Carbonic anydrase has the 2″ fastest turnover number; therefore, it is 2nd fastest active enzyme (after catalase). Lysozyme has the lowest turnover number and therefore is slowest acting.

Quiz In Between



Isoenzymes

ISOENZYMES


ISOENZYMES (ISOZYMES)

  • Isoenzymes are the physically distinct forms of the same enzyme.
  • Isoenzymes differ from each other structurally, electrophoretically and immunologically.
  • Isoenzymes possess quaternary structure and are made up of two or three different subunit (mutimeric).
  • Isoenzymes catalyze the same reaction and act on same substrate, but with different Km and Vmax values i.e. isozymes have different kinetics.

Plasma Enzymes-

  • Functional plasma enzymes- specific function in the plasma. E.g. Coagulation factors (thrombin), lipoprotein lipase, clotting factors.
  • Non functional enzymes- E.g. alkaline phosphatase, acid phosphatase, gamma glutamyl transpeptidase, LDH, Creatine kinase.

Lactate Dehydrogenase (LDH)

  • LDH with two subunits- H(heart) and M(muscle)
  • It has five isoenzymes.
Name of the isoenzyme Tissue location
LDH-1 Heart muscle
LDH-2 RBC
LDH-3 Brain
LDH-4 Liver and skeletal muscle
LDH-5 Liver and skeletal muscle
  • In MI, LDH1 is raised more than LDH2.
  • Normal LDH pattern on electrophoresis is LDH2 > LDHI > LDH 3 > LDH 4>LDH5
  • Increased in LDH level- pancreatitis.

Creatine Kinase (CK)

  • Three isoenzymes.
  • It is subunit M(myocardium) and B (Brain).
Name of isoenzyme Tissue localisation
CK-1 Brain
CK-2 Heart
CK-3 Skeletal Muscle

Alkaline Phosphatase (ALP)-

Isoenzyme Tissue Location
Alpha-1 ALP Epithelial cells of biliary canaculi
Alpha-2 heat liable ALP Hepatic cells
Alpha-2 heat stable ALP Placenta (Inhibited by Phenylalanine)
Pre beta ALP Osteoblast
Gamma ALP Intestinal cells
Leukocyte ALP Leukocytes
  • Raised activity of alkaline phosphatase is useful in diagnosis of bone and liver pathology.

 Transaminase-

  • Aspartate Transaminase- increase in myocardium.
  • Mitochondrial isoenzyme present in liver.
  • Alanine Transaminase (ALT)-  mainly in liver and entirely in Cytoplasm. 

Protease-

  • Serine Proteasesserine residue at the active site(serine, histidine, aspirate).
  • E.g.- Trypsin, chymotrypsin, elastase (catalytic traid)
  • Inhibited by disopropylphosphofluridate binds covalently to serine residue.
  • Activated in intestine by proteolytic activation.

Carboxyl or acid Proteases-

  • Most important carboxyl proteases is Pepsin.

Exam Important

  1. Isoenzymes differ from each other structurally, electrophoretically and immunologically.
  2. Isoenzymes possess quaternary structure and are made up of two or three different subunit (mutimeric).
  3. Functional plasma enzymes- specific function in the plasma.- E.g. Coagulation factors (thrombin), lipoprotein lipase, clotting factors.
  4. Non functional enzymes  E.g. alkaline phosphatase, acid phosphatase, gamma glutamyl transpeptidase, LDH, Creatine kinase.
  5.  LDH has five isoenzymes.
Name of the isoenzyme Tissue location
LDH-1 Heart muscle
LDH-2 RBC
LDH-3 Brain
LDH-4 Liver and skeletal muscle
LDH-5 Liver and skeletal muscle

 6. In MI, LDH1 is raised more than LDH2.

 7. Creatine Kinase (CK)- Three isoenzymes.

CK-1 Brain
CK-2 Heart

 8. ALP found in liver, bone, kidney, intestinal mucosa and placenta.

9. Serine Proteasesserine residue at the active site(serine, histidine, aspirate).

10. Serine proteases- E.g.- Trypsin, chymotrypsin, elastase (Catalytic triad).

11. Serine proteases activated in intestine by proteolytic activation.

12.  Most important carboxyl proteases is Pepsin.

Don’t Forget to Solve all the previous Year Question asked on ISOENZYMES

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