CR III - Metabolism of Amino Acids

Question 1

What are 5 that are essential for deriving coenzymes from for amino acid metabolism?

Answer 1

Vit B6
Folic acid
B12
Biotin
Niacin

Question 2

What are the 9 (10) essential AA?

Answer 2

P - phenylalanine
V - valine
T - threonine
T - tryptophan
I - isoleucine
M - methionine
H - histidine
A - arginine (children only)
L - leucine
L - Lysine

Question 3

What is tyrosine synthesized from? Cysteine?

Answer 3

Tyrosine - synthesized from phenylalanine

Cysteine - synthesized from methionine

Question 4

What do most transaminases require, one for each direction, of the reversible reaction?

Answer 4

Alpha-ketoglutarate (when converting AA to a-keto acid)

Glutamate - (when converting a-keto acid to AA)

Question 5

What do all transaminases require as a prosthetic group? What is this derived from?

Answer 5

Pyridoxal phosphate

Derived from Vit B6

Question 6

What are the only two AA that are not substrates for reversible transamination?

Answer 6

Lysine

Threonine

Question 7

What are glycogenic AA? Ketogenic?

Answer 7

Glycogenic - AA whose carbon skeleton can be converted to glucose
Ketogenic - AA whose carbon skeletons can be converted into ktone bodies or acetyl Co-A (but not glucose)

Question 8

Can AA be both ketogenic and glycogenic?

Answer 8

Yes

Question 9

What are the two intermediates of the TCA cycle that can be used as the carbon skeletons for AA? Which AA can each produce? (One has 4, one has 2)

Answer 9

Alpha-ketoglutarate - glutamate, glutamine, proline, arginine
Oxaloacetate - aspartate, asparagine

Question 10

Which two essential amino acids each act as a carbon skeleton for 2 other AA? Which ones?

Answer 10

Phenylalanine - tyrosine

Methionine - cysteine

Question 11

What quantitatively is the most important glycogenic AA?

Answer 11

Alanine

Question 12

How is asparagine made from aspartate? How is it converted back to aspartate? Are they glycogenic, ketogenic, or both?

Answer 12

Aspargine synthase and glutamine are needed to convert aspartate to asparagine
Asparaginase is used to catabolize asparagine to aspartate
Both are glycogenic

Question 13

What types of AA are valine, leucine, and isoleucine? What end products are created by each (one for valine, 2 for each of the others)? Are each glycogenic, ketogenic, or both?

Answer 13

Branched AA
Valine - propionyl CoA - glycogenic
Leucine - acetoacetate and acetyl CoA - ketogenic
Isoleucine - propionyl CoA and acetyl CoA - both

Question 14

What two enzymes are involved in converting valine, leucine, and isoleucine to their end products? Deficiency in which one results in MSUD?

Answer 14

AA transaminase

A-keto acid dehydrogenase

Question 15

What is propionyl CoA converted to so it can enter the TCA cycle? What enzyme in this process requires a cofactor derived from B12?

Answer 15

Succinyl CoA

Methylmalonyl Mutase

Question 16

Besides serines ability to come from are be metabolized to 3-phosphoglycerate, what two other products can it form? What do both require?

Answer 16

Pyruvate
Glycine
Both require pyridoxal phosphate

Question 17

To make glycine, what does serine need besides pyridoxal phosphate? What is this a metabolite of? What is it involved in?

Answer 17

Tetrahydrofolate (THF)
Metabolite of folic acid
Involved in one carbon metabolism

Question 18

What are three end products for Threonine? Which one is the major pathway? Is threonine ketogenic, glycogenic, or both?

Answer 18

Propionyl CoA
Glycine - major pathway
Pyruvate
Both ketogenic and glycogenic

Question 19

Besides serine (and THF) and threonine, how can glycine be formed? What 4 things does this require? Why is this special?

Answer 19

From its own parts
CO2, NH4, methylene THF, and pyridoxal phosphate
Only AA that can form from its individual parts

Question 20

Which pathway of catabolization of serine is least common?

Answer 20

Threonine pathway

Question 21

Is glycine ketogenic, glycogenic, or both? why?

Answer 21

Glycogenic

because it can revert back to serine which is glycogenic

Question 22

What is THF derived from? What is its main purpose?

Answer 22

Vitamin folic acid

Serves to transfer 1 carbon units

Question 23

What are 4 important uses of THF?

Answer 23

Serine, glycine, and histidine
Resynthesize methionine from homocysteine
Synthesis of purines
Formation of methyl group of thymine

Question 24

What internediate is shared in the synthesis and catabolism of proline, arginine, glutamine, and the catabolism of histidine? Why is its conversion to glutaime important?

Answer 24

Glutamate

Glutmine - non-toxic way of transporting ammonia in the blood

Question 25

What tissue is high in glutaminase activity? What is its function?

Answer 25

Kidney

To remove ammonia and excrete it

Question 26

Are glutamate, glutamine, arginine, proline, and histidine glycogenic or ketogenic?

Answer 26

Glycogenic

Question 27

What are the two fates of homocysteine? Which one requires a special co-factor?

Answer 27

Homocystine - converts to cysteine or methionine

Conversion to methionine requires vit B12

Question 28

What is cysteine eventually converted to? Does this make is ketogenic or glycogenic?

Answer 28

Pyruvate

Glycogenic

Question 29

All phenylalanine that is not used for protein synthesis is converted to what?

Answer 29

Tyrosine

Question 30

What are both phenylalanine and tryosine catabolized to? Does this make them glycogenic or ketogenic?

Answer 30

Fumarate and acetoacetate

Both glycogenic and ketogenic

Question 31

Regardless of which catabolic pathway you take (of 2), what other enzyme will the catabolism of tryptophan produce? What can be produced from one pathway? Why is it important?

Answer 31

Alanine
Quinolinic acid
Clinically significant source of NAD(P) in liver