L31- Amino Acid Synthesis

Question 1

Which cofactor is required for the conversion of tyrosine to dopamine?

Answer 1

Tetrahydrobiopterin (THB)

Question 2

Which enzyme catalyzes the conversion of 3,4-dihydroxyphenylalanine (Dopa) to dopamine?

Answer 2

Dopa decarboxylase.

Question 3

How is thyroxine synthesized?

Answer 3

It is made from the iodination of two tyrosines residues on thyroglobulin.

Question 4

Which pigment molecule in the skin and eyes is made from tyrosine?

Answer 4

Melanin.

Question 5

Which enzyme deficiency results in albinism?

Answer 5

Tyrosinase deficiency.

Question 6

What is the function of S-adenosyl methionine?

Answer 6

It transfers methyl groups.

Question 7

Which coenzyme catalyzes the transfer of one-carbon fragments from formic acid to methyl groups?

Answer 7

Tetrahydrofolate (THF).

Question 8

Which form of tetrahydrofolate (THF) is most effective for the transfer of one-carbon fragments?

Answer 8

The polyglutamyl form (the other form is the methyl derivative, which is the major form of THF in the blood).

Question 9

From which vitamin is tetrahydrofolate derived?

Answer 9

Vitamin B9 (folic acid).

Question 10

From which amino acids can one-carbon fragments be synthesized?

Answer 10

Glycine, serine, histidine and, to some extent, tryptophan.

Question 11

Which enzyme reduces dihydrofolate to its functionally active form, tetrahydrofolate?

Answer 11

Dihydrofolate reductase.

Question 12

Which step in the formation of 5-methyl THF from THF is irreversible?

Answer 12

The conversion of 5,10-methylene THF to 5-methyl THF by methylene reductase.

Question 13

Which enzyme regenerates THF from 5-methyl THF?

Answer 13

Methionine synthase.

Question 14

Methionine synthase requires what cofactor for proper activity?

Answer 14

Vitamin B12 (in the form of methylcobalamin).

Question 15

Which amino acid can be derived from the action of serine hydroxymethylase on a serine molecule?

Answer 15

Glycine.

Question 16

Which coenzyme is required for activity of Dopa decarboxylase?

Answer 16

Pyridoxal phosphate (PLP).

Question 17

Which coenzyme is required for activity of serine hydroxymethylase?

Answer 17

Pyridoxal phosphate (PLP).

Question 18

Which tetrahydrofolate (THF) derivative is most abundant in plasma?

Answer 18

5-methyl THF.

Question 19

What is the product of the reaction catalyzed by serine dehydratase?

Answer 19

Pyruvate.

Question 20

Which birth defect is associated with low folate during pregnancy?

Answer 20

Spina bifida.

Question 21

Which folate analogue interferes with the growth of rapidly growing cells by interfering with pyrimidine synthesis?

Answer 21

Methotrexate.

Question 22

Which analgue of p-aminobenzoic acid can block synthesis of folate in bacteria but not in humans?

Answer 22

Sulfanilamides.

Question 23

Which compound directly derived from methionine is involved in the transfer of methyl groups?

Answer 23

S-adenosylmethionine.

Question 24

S-adenosylmethionine converts into which compound upon donation of its methyl group?

Answer 24

S-adenosylhomocysteine.

Question 25

What cofactor is required for the conversion of norepinephrine to epinephrine?

Answer 25

S-adenosylmethionine.

Question 26

Which amino acids are directly involved in the synthesis of creatine?

Answer 26

Glycine, arginine and methionine.

Question 27

What are two ways in which free homocysteine can be converted to methionine?

Answer 27

A methyl group can be transferred from 5-methyl THF or a methyl group can be transferred from choline.

Question 28

What is the only enzyme that has the ability to regenerate THF from methyl-THF?

Answer 28

Methionine synthase.

Question 29

Dietary deficiency of which vitamin can lead to a deficiency in functional folate?

Answer 29

Vitamin B12.

Question 30

Which major component of bile acids is derived from cysteine?

Answer 30

Taurine.

Question 31

Which amino acids serve as precursors for the synthesis of cysteine?

Answer 31

Methionine and serine.

Question 32

What are the products of the breakdown of cystathione by the enzyme cystathionase?

Answer 32

Cysteine and alpha-ketobutyrate.

Question 33

Increased levels of which non-protein amino acid are associated with folate metabolism abnormalities?

Answer 33

Homocysteine.

Question 34

True or False. Increased levels of homocysteine are associated with an increased risk of arterial disease.

Answer 34

True.

Question 35

Which branched chain amino acids are preferentially metabolized for the production of ATP in muscle?

Answer 35

Valine, leucine and isoleucine.

Question 36

Which amino acid can be directly transaminated to pyruvate for gluconeogenesis in the liver?

Answer 36

Alanine.

Question 37

Which amino acid is used by the liver for either the production of ammonia or the synthesis of glutamate?

Answer 37

Glutamine.

Question 38

What is the function of glutaminase in the kidneys?

Answer 38

Glutaminase generates glutamate and ammonium ions from glutamine. In the kidneys, this serves to increase the amount of ammonium ions excreted.

Question 39

Which amino acid is preferentially used for energy production in the intestines?

Answer 39

Glutamine.