Amino Acid (AA) synthesis and degradation

Question 1

How many of 20 AA can humans synthesize?

Answer 1

11 can be synthesized, the other 9 are considered essential.

Question 2

What are the 3 most important cofactors in AA synthesis?

Answer 2

pyridoxal phosphate (PLP)
tetrahydrobiopterin (BH4)
tetrahydrofolate (FH4)

Question 3

What is pyridoxal phosphate (PLP) used for?

Answer 3

This is primarily used for transamination reactions.

Question 4

This is primarily used for transamination reactions.

Answer 4

pyridoxal phosphate (PLP)

Question 5

What is tetrahydrobiopterin (BH4) used for?

Answer 5

This is required for hydroxylation reactions

Question 6

This is required for hydroxylation reactions

Answer 6

tetrahydrobiopterin (BH4)

Question 7

What is tetrahydrofolate (FH4) used for?

Answer 7

This is required for one-carbon metabolism.

Question 8

This is required for one-carbon metabolism.

Answer 8

tetrahydrofolate (FH4)

Question 9

Which nonessential AA can be synthesized from glycolytic intermediates

Answer 9

Serine, glycine, cystieine, and pyruvate

Question 10

Which nonessential AA can be synthesized from TCA cycle intermediates?

Answer 10

Aspartate, Asparagine, Glutamaine, Proline, Arginine, and Ornithine

Question 11

Which nonessential AA can be synthesized from existing (essential) amino acids?

Answer 11

Tyrosine (from phenylalanine)

Cysteine (sulfur from methionine)

Question 12

What is the difference between a glucogenic or ketogenic amino acid?

Answer 12

When AA are degraded and the nitrogen is converted to urea, all that is left is the carbon skeletons. Some are precursors of glucose and others are precursors of ketone bodies.
(tryptophan is both)

Question 13

PKU

classic and nonclassical

Answer 13

Classical PKU = defect in phenylalanine hydroxylase.
Nonclassic PKU = defect in dihydropterindine reductase.
Both cause accumulation of phenylalanine and cause mental retardation if treatment not initiated early.
Treatment: restrict dietary phenylalanine.

Question 14

Alcaptonuria

Answer 14

Caused by defect in homogentisate oxidase, an enzyme in tyrosine metabolism. Leads to accumulation of homogentisic acid, which forms a dark pigment. This presents as dark urine in infants that stains diapers. Later in life, chronic accumulation in joints may cause arthritis.

Question 15

Tyrosinemia

type 1 and type 2

Answer 15

Type 1 - defect in fumarylacetoacetate leading to liver failure and early death
Type 2 - defect in tyrosine aminotransferase leading to neurologic defects.

Question 16

Cystathioninuria

Answer 16

defect in cystathionase leading to accumulation of cystathionine.
(no major complications of this mutation)

Question 17

Homocysteinemia

Answer 17

A defect in the cystathionine beta-synthase, leads to accumulation of homocysteine, results in cardiologic and neurologic complications.

Question 18

Primary oxaluri type 1

Answer 18

defect in glycine transaminase leading to oxalate accumulation and renal failure due to kidney stone formation.

Question 19

Maple syrup urine disease

Answer 19

defect in the branched-chain alpha-keto acid dehydrogenase, accumulation of a-keto acids resulting in mental retardation.

Question 20

cystinosis

Answer 20

defect in the transport protein that carries cystine across lysosomal membranes. cysteine accumulates in the lysosomes, interfering with and eventually destroying their function.

Question 21

Thiamine deficiency

Answer 21

Leads to accumulation of a-keto acids because the enzymes that catalyze oxidative decarboxylation reactions will not function without it. This messes up energy production and leads to ketoacidosis.