Amino Acid Metabolism

Q1: The most toxic compounds is

A tyrosine

B phenylpyruvate

C lysine

D phenylalanine

ANS:B - phenylpyruvate

Phenylpyruvate is formed when phenylalanine loose its amino group. Accumulation of phenylalanine will increase the levels of phenylpyruvate and deprives the brain of alph ketoglutarate which will cause the brain to shut the TCA cycle and hence aerobic respiration. This condition is known as phenylketonuria victims start to have mental issues.

It can again inhibit the expression of tyrosinase enzyme leading to deficiency of pigmentation.

Q2: A best described ketogenic amino acid is

A lysine

B tryptophan

C valine

D none of these

ANS:A - lysine

Please explain the answer.

Q3: Lysine is degraded to acetoacetyl CoA and is described as a

A ketogenic amino acid

B glucogenic amino acid

C keto-gluco amino acid

D none of these

ANS:A - ketogenic amino acid

This is because of ketogenic amino acid when undergoes metabolism it leads to the production of acetoacetyl CoA which is a precursor for the production of ketone bodies.

Q4: A person suffering from phenylketonuria on consumption food containing high phenylalanine may lead to the accumulation of

A phenylalanine

B phenylpyruvate

C tyrosine

D isoleucine

ANS:B - phenylpyruvate

Phe convert to tyrosine by enzyme called phe hydroxylase.

So when this enzyme deficiency phe convert to anther pathway which is toxic and result is phenylpyruvate.

Q5: Transamination is the transfer of an amino

A acid to a carboxylic acid plus ammonia

B group from an amino acid to a keto acid

C acid to a keto acid plus ammonia

D group from an amino acid to a carboxylic acid

ANS:B - group from an amino acid to a keto acid

No answer description is available.

Q6: Transaminase enzymes are present in

A liver

B pancreas

C intestine

D none of these

ANS:A - liver

No answer description is available.

Q7: A person with phenylketonuria will convert

A phenylalanine to phenylpyruvate

B phenylalanine to isoleucine

C phenylpyruvate to phenylalanine

D tyrosine to phenylalanine

ANS:A - phenylalanine to phenylpyruvate

I think this answer is wrong because in PKU when phenylalanine is accumulated it is converted to phenylpyruvate and this is the toxic substance.

Q8: Transamination is the process where

A carboxyl group is transferred from amino acid

B α-amino group is removed from the amino acid

C polymerisation of amino acid takes place

D none of the above

ANS:B - α-amino group is removed from the amino acid

Removal of the amino group means getting free ammonia.
So, it is deamination, not transamination.

Q9: Histidine is degraded to α-ketoglutarate and is described as a

A gluco amino acid

B glucogenic amino acid

C ketogenic amino acid

D keto-gluco amino acid

ANS:B - glucogenic amino acid

Histidine is deaminated to urocanic acid, which is converted to 4-imidazolone 5-propionate. Hydrolysis of the later gives N-formiminoglutamate (FIGlu, which donates its formimino group to tetrahydrofolate, leaving glutamate which is then converted to alpha-ketoglutarate. Alpha-ketoglutarate is an intermediate in the Kreb's Cycle. Any amino acid whose catabolism gives pyruvate or one of the intermediate of Citric Acid Cycle is glycogenic amino acid.

Q10: Oxidative deamination is the conversion of an amino

A group from an amino acid to a keto acid

B acid to a carboxylic acid plus ammonia

C acid to a keto acid plus ammonia

D group from an amino acid to a carboxylic acid

ANS:C - acid to a keto acid plus ammonia

In oxidative diamination there should be ammonia as by product which distinguishes it from deamination where there is no production of ammonia as keto acid is obtain from both deamination and oxidative diamination.

Q11: Which of the following is the best described glucogenic amino acid?

A Lysine

B Tryptophan

C Valine

D None of these

ANS:C - Valine

Is valine regarded as the best described glucogenic because it is ONLY glucogenic and not ketogenic too?

Q12: A person with phenylketonuria is advised not to consume which of the following products?

A Glycine containing foods

B Fat containing food

C Glucose

D Aspartame

ANS:D - Aspartame

Aspartame is a methyl ester of the aspartic acid/phenylalanine dipeptide.

Hydrolysis of aspartame produces phenylalanine in the body.

Phenylketonurics have deficient phenylalanine hydroxylase required for the metabolism of phenylalanine, thus phenylalanine accumulation takes place and produces toxic products like phenylpyruvate via transamination.

Q13: A person with phenylketonuria cannot convert

A phenylalanine to tyrosine

B phenylalanine to isoleucine

C phenol into ketones

D phenylalanine to lysine

ANS:A - phenylalanine to tyrosine

Disease conditions in amino acid metabolism is usually due to the lack of certain enzymes, phenylketonuria is due to the lack of phenylalanine hydroxylase, which is the enzyme involved in the conversion of phenylalanine to tyrosine. While ALkaptonuria is due to the lack of homogentisate dioxygenase in the conversion of Homogentisate to Maleylacetoacetate both of which are intermediates in the total conversion of phenylalanine to acetoacetyl coA.

Q14: An example of a transamination process is

A glutamate = hexanoic acid + NH3

B aspartate + hexanoic acid = glutamate + oxaloacetate

C aspartate + α ketoglutarate = glutamate + oxaloacetate

D glutamate = α-ketoglutarate + NH3

ANS:C - aspartate + α ketoglutarate = glutamate + oxaloacetate

In transamination, the alpha amino group is transferred to one amino acid to one keto acid and new amino acid is formed.

Q15: Tyrosine is degraded to acetoacetyl CoA and fumarate and is described as a

A glucogenic amino acid

B ketogenic amino acid

C ketogenic and glucogenic amino acid

D keto-gluco amino acid

ANS:C - ketogenic and glucogenic amino acid

No answer description is available.

Q16: In the normal breakdown of phenylalanine, it is initially degraded to

A fumarate

B tyrosine

C lysine

D phenylpuruvate

ANS:B - tyrosine

No answer description is available.

Q17: A glucogenic amino acid is one which is degraded to

A keto-sugars

B either acetyl CoA or acetoacetyl CoA

C pyruvate or citric acid cycle intermediates

D none of the above

ANS:C - pyruvate or citric acid cycle intermediates

Glucogenic amino acid are those that their carbon skeleton is degraded to pyruvate or alpha keto glutarate which is a TCA cycle intermediate.

Q18: Which of the following amino acids is considered as both ketogenic and glucogenic?

A Valine

B Tryptophan

C Lysine

D None of these

ANS:B - Tryptophan

Tryptophan is both an essential amino acid and both a ketogenic and glycogenic amino acid.

Q19: An example of the oxidative deamination is

A glutamate = hexanoic acid + NH3

B aspartate + α-ketoglutarate = glutamate + oxaloacetate

C glutamate = α-ketoglutarate + NH3

D aspartate + hexanoic acid = glutamate + Oxaloacetate

ANS:C - glutamate = α-ketoglutarate + NH3

No answer description is available.

Q20: A ketogenic amino acid is one which degrades to

A keto-sugars

B either acetyl CoA or acetoacetyl CoA

C pyruvate or citric acid cycle intermediates

D multiple intermediates including pyruvate or citric acid cycle intermediates and acetyl CoA or acetoacetyl CoA

ANS:B - either acetyl CoA or acetoacetyl CoA

No answer description is available.



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