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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