Tryptophan

Tryptophan

Q. 1 Melatonin is secreted by parenchymal cells of pineal gland. Fever causes:
 A Thermoregulatory centre to shift to new level
 B Resetting of skin temperature
 C Both of the above
 D None of the above
Q. 1 Melatonin is secreted by parenchymal cells of pineal gland. Fever causes:
 A Thermoregulatory centre to shift to new level
 B Resetting of skin temperature
 C Both of the above
 D None of the above
Ans. A

Explanation:

Thermoregulatory centre to shift to new level


Q. 2

For each description, choose the neurotransmitter with which it is usually associated: Ingestion of l-tryptophan increases the levels of this substance in the brain.

 A

Serotonin

 B

Norepinephrine

 C

Dopamine

 D

Acetylcholine

Q. 2

For each description, choose the neurotransmitter with which it is usually associated: Ingestion of l-tryptophan increases the levels of this substance in the brain.

 A

Serotonin

 B

Norepinephrine

 C

Dopamine

 D

Acetylcholine

Ans. A

Explanation:

The amino acid l-tryptophan is the precursor for serotonin, which is a neurotransmitter needed for non-rapid-eye–movement (NREM) sleep as well as for mood and pain modulation.
Up to 70 to 90% of brain norepinephrine is produced in the pontine nucleus, locus ceruleus.
Dopamine is implicated in schizophrenia and also in an important neurotransmitter for the extra-pyramidal system.
Depletion of this substance, as in parkinsonism, causes muscular rigidity and tremors.
Acetylcholine is the neurotransmitter associated with higher cortical functioning and is depleted in Alzheimer’s disease.
Acetylcholine also is an important neurotransmitter for the autonomic nervous system (parasympathetic system and the sympathetic nerves to the sweat glands).
Many antidepressants have an anticholinergic action, thus dryness of the mouth, constipation, and blurred vision.
GABA is an important inhibitory transmitter that opens the chloride channels directly associated with the GABA receptors, hyperpolarizing the cell.
 
Ref: Meltzer H.Y., Bobo W.V., Heckers S.H., Fatemi H.S. (2008). Chapter 16. Schizophrenia. In M.H. Ebert, P.T. Loosen, B. Nurcombe, J.F. Leckman (Eds),CURRENT Diagnosis & Treatment: Psychiatry, 2e.

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.

Q. 4

Which of the following is the 1st product of tryptophan catabolism?

 A

Xantheurenate

 B

Kynurenine

 C

PAF

 D

Bradykinin

Q. 4

Which of the following is the 1st product of tryptophan catabolism?

 A

Xantheurenate

 B

Kynurenine

 C

PAF

 D

Bradykinin

Ans. B

Explanation:

Tryptophan is degraded to amphibolic intermediates via the kynurenine-anthranilate pathway.

Tryptophan oxygenase converts tryptophan to N formyl kynurenine by opening the indole ring and by incorporating molecular oxygen.

This inturn is catalysed by kynurenine formylase to produce kynurenine.

Hartnup’s disease result from impaired intestinal and renal transport of tryptophan and other neutral amino acids.

This defect accounts for deficient niacin biosynthesis resulting in pellagra like signs and symptoms.

Ref: Harper’s Illustrated Biochemistry, 29e, Chapter 29


Q. 5

Melatonin, plays an important role in sleep-wake cycle, is secreted by:

 A

Pineal gland

 B

Thyroid gland

 C

Ant. pituitary

 D

Pancreas

Q. 5

Melatonin, plays an important role in sleep-wake cycle, is secreted by:

 A

Pineal gland

 B

Thyroid gland

 C

Ant. pituitary

 D

Pancreas

Ans. A

Explanation:

 
Melatonin is an endogenous hormone that is normally secreted by the pineal gland and is believed to be involved with the circadian sleep-wake cycle.
 
Melatonin synthesis and secretion are increased during the dark period of the day and maintained at a low level during daylight hours. This diurnal variation in secretion is brought about by norepinephrine secreted by the postganglionic sympathetic nerves that innervate the pineal gland.
 
Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 14. Electrical Activity of the Brain, Sleep—Wake States, & Circadian Rhythms. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.

 


Q. 6

The following is false about Tryptophan

 A

Non essential amino acid

 B

Involved in serotonin synthesis

 C

Involved in niacin synthesis

 D

Involved in melatonin synthesis

Q. 6

The following is false about Tryptophan

 A

Non essential amino acid

 B

Involved in serotonin synthesis

 C

Involved in niacin synthesis

 D

Involved in melatonin synthesis

Ans. A

Explanation:

Q. 7

Melatonin is secreted by:

 A

Hypothalamus

 B

Adrenal cortex

 C

Pineal gland

 D

Melanocytes

Q. 7

Melatonin is secreted by:

 A

Hypothalamus

 B

Adrenal cortex

 C

Pineal gland

 D

Melanocytes

Ans. C

Explanation:

C i.e. Pineal gland

Melatonin is synthesized & secreted by pineal glandQ.


Q. 8

Exposure to darkness leads to increased melatonin secretion.

It is brought about by:

 A

Decreasing the activity of suprachiasmatic nuclei

 B

Increasing the serotonin N-acetyl transferase

 C

Decreasing the hydroxy-indole-o-methyl transferase, activity

 D

Blocking the release of norepinephrine from sympathetic nerve terminals

Q. 8

Exposure to darkness leads to increased melatonin secretion.

It is brought about by:

 A

Decreasing the activity of suprachiasmatic nuclei

 B

Increasing the serotonin N-acetyl transferase

 C

Decreasing the hydroxy-indole-o-methyl transferase, activity

 D

Blocking the release of norepinephrine from sympathetic nerve terminals

Ans. B

Explanation:

B i.e. Increasing the serotonin N- acetyl transferase

Increased in N-acetyl transferase of hydroxy indole-o-methyl (HOM) transferase activity in darkness Vt increased melatonin secretionQ


Q. 9

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

 A

22

 B

37

 C

55

 D

60

Q. 9

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. 10

Melatonin is associated with all of the following except: 

March 2010

 A

Vomiting

 B

Pituitary gland secretion

 C

Sleep mechanism

 D

Jetlag

Q. 10

Melatonin is associated with all of the following except: 

March 2010

 A

Vomiting

 B

Pituitary gland secretion

 C

Sleep mechanism

 D

Jetlag

Ans. A

Explanation:

Ans. A: Vomiting

Melatonin and the enzymes responsible for its synthesis from serotonin by N-acetylation and 0-methylation are present in pineal parenchymal cells, and the hormone is secreted by them into the blood and the cerebrospinal fluid. Melatonin synthesis and secretion are increased during the dark period of the day and maintained at a low level during the daylight hours. This remarkable diurnal variation in secretion is brought about by norepinephrine secreted by the postganglionic sympathetic nerves (nervi conarii) that innervate the pineal. The norepinephrine acts via -adrenergic receptors in the pineal to increase intracellular cAMP, and the cAMP in turn produces a marked increase in N-acetyltransferase activity. This results in increased melatonin synthesis and secretion.

Effects of Melatonin:

  • It plays a role in sleep mechanism
  • It is supposed to decrease gonadotropic hormone secretion by anterior pituitary

Vomiting centre is located in the brain stem. From here, motor impulses that cause the actual vomiting are transmitted from the vomiting center by the way of the 5th,7th,9th,10th and 12th cranial nerves to the upper GIT, through vagal and sympathetic nerves to the lower tract and through spinal nerves to the diaphragm and abdominal vessels.


Q. 11

Metabolism of which of the following amino acid is at fault in Hartnup’s disease:

 A

Tryptophan

 B

Sulfur amino acids

 C

Glycine

 D

Histidine

Q. 11

Metabolism of which of the following amino acid is at fault in Hartnup’s disease:

 A

Tryptophan

 B

Sulfur amino acids

 C

Glycine

 D

Histidine

Ans. A

Explanation:

 

Abnormal metabolism of amino acids and conditions

  • Hartnup’s disease is a hereditary disorder of tryptophan metabolism
  • Sulfur amino acids (methionine, cysteine and cystine) metabolism disorder results in cystinuria, cystinosis, homocystinuria and cystathionuria
  • Disorder of glycine metabolism results in glycinuria and primary hyperoxaluria
  • Defect in metabolism of histidine results in histidinemia

Q. 12

Hartnup’s disease is associated with increased urinary excretion of:   

 A

Tryptophan

 B

Ornithine

 C

Glycine

 D

Cystine

Q. 12

Hartnup’s disease is associated with increased urinary excretion of:   

 A

Tryptophan

 B

Ornithine

 C

Glycine

 D

Cystine

Ans. A

Explanation:

 

Hartnup’s disease is characterized by low plasma levels of tryptophan and other neutral amino acids and their elevated urinary excretion


Q. 13

Which of the following is found in urine in Hartnup’s disease patients?       

 

 A

Phenyalanine

 B

Ornithine

 C

Cystine

 D

None

Q. 13

Which of the following is found in urine in Hartnup’s disease patients?       

 

 A

Phenyalanine

 B

Ornithine

 C

Cystine

 D

None

Ans. D

Explanation:

 

Hartnup disease is inherited as an autosomal recessive trait.

Heterozygotes are normal. Consanguinity is common.


Q. 14

Which of the following is caused by defective transport of tryptophan?

 A

Hartnup disease

 B

Maple syrup urine disease

 C

Alkaptonuria

 D

Phenylketonuria

Q. 14

Which of the following is caused by defective transport of tryptophan?

 A

Hartnup disease

 B

Maple syrup urine disease

 C

Alkaptonuria

 D

Phenylketonuria

Ans. A

Explanation:

 

Hartnup disease

  • It is an inherited disorder in the metabolism of tryptophan.
  • It is due to defective transport of tryptophan and other neutral amino acids in the intestine and kidney.
  • This results in deficiency of tryptophan leading to decreased synthesis of niacin and serotonin.
  • Thus there are pellagra (niacin deficiency), neurological symptoms (serotonin deficiency) and amino aciduria due to defective transport of amino acids in kidney.

Q. 15

In pyridoxine deficiency, tryptophan is converted to ‑

 A

Nicotine

 B

Acetoacetate

 C

Xantheurenic acid

 D

Acetyl CoA

Q. 15

In pyridoxine deficiency, tryptophan is converted to ‑

 A

Nicotine

 B

Acetoacetate

 C

Xantheurenic acid

 D

Acetyl CoA

Ans. C

Explanation:

Ans. is ‘c’ i.e., Xantheurenic acid


Q. 16

Hartnup disease is related to ‑

 A

Rickets symptoms

 B

Pellagra symptoms

 C

Burning foot syndrome

 D

Angular stomatitis

Q. 16

Hartnup disease is related to ‑

 A

Rickets symptoms

 B

Pellagra symptoms

 C

Burning foot syndrome

 D

Angular stomatitis

Ans. B

Explanation:

 

Hartnup disease

It is an inherited disorder in the metabolism of tryptophan.

It is due to defective transport of tryptophan and other neutral amino acids in the intestine and kidney.

This results in deficiency of tryptophan leading to decreased synthesis of niacin and serotonin.

Thus there are pellagra (niacin deficiency), neurological symptoms (serotonin deficiency) and amino aciduria due to defective transport of amino acids in kidney.


Q. 17

Tryptophan is glucogenic & ketogenic by producing 

 A

Acetyl CoA & alanine

 B

Acetoacetate & fumarate

 C

Acetoacetate & arginine

 D

Arginine & alanine

Q. 17

Tryptophan is glucogenic & ketogenic by producing 

 A

Acetyl CoA & alanine

 B

Acetoacetate & fumarate

 C

Acetoacetate & arginine

 D

Arginine & alanine

Ans. A

Explanation:

Ans. is ‘a’ i.e., Acetyl CoA & alanine


Q. 18

Melatonin is derived from ‑

 A

Tyrosine

 B

Tryptophan

 C

Glutathione

 D

None

Q. 18

Melatonin is derived from ‑

 A

Tyrosine

 B

Tryptophan

 C

Glutathione

 D

None

Ans. B

Explanation:

Ans. is ‘b’ i.e., Tryptophan



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