MTC exam II week II

Question 1

What is the general design of amino acid degradation? What are the exceptions?

Answer 1

transfer the alpha amino group from the amino acid to alpha-ketogluterate. this forms glutamate and an alpha keto acid
exceptions: lys, thr, glutamate

Question 2

ALT

Answer 2

alanine amino transferase

alanine + alpha-ketogluterate –> pyruvate + glutamate

Question 3

AST

Answer 3

aspartate + alpha-ketogluterate –> oxaloacetate + glutamate

Question 4

What is one co-factor required by amino transferases? What is their mechanism of action?

Answer 4

PLP, a B6 derivative. these are ping-pong enzymes

Question 5

Where does oxidative deamination take place? What are the reactants and products? What is the enzyme?

Answer 5

mitochondria of liver and kidney. glutamate +NAD(P) –> alphaketogluterate + ammonia + NAD(P)H
enzyme is L-glutamate Dehydrogenase

Question 6

L glutamate dehydrogenase

Answer 6

converts glutamate and NAD(P) into ammonia and alpha ketogluterate and NAD(P)H in the mitochondria of the liver and kidneys

Question 7

what two amino acids are exclusively ketogenic?

Answer 7

Leu and Lys

Question 8

What two amino acids are both ketogenic and glucogenic?

Answer 8

Phe, Iso, Tyr, Trp, Thr

Question 9

what amino acids can be broken down to form pyruvate?

Answer 9

alanine, cystein, serine, and part of tryptophan

Question 10

what amino acids are broken down to form alpha ketogluterate?

Answer 10

glutamin, glutamate proline

Question 11

What amino acids form oxaloacetate?

Answer 11

aspartate and asparagine

Question 12

what amino acids form acetoacetyl CoA

Answer 12

tryptophan (part of) and lysine

Question 13

What amino acids require the transfer of a single Carbon?

Answer 13

Thr, His, Met, Gly

Question 14

When is biotin used as a cofactor in amino acid degredation?

Answer 14

biotin is used as a cofactor when you need to make a new carboxyl group from CO2, as in the degradation of Val, Met, Iso, Thr

Question 15

What enzyme generates THF from folate?

Answer 15

dihydrofolate reductase

Question 16

dihydrofolate reductase

Answer 16

generates THF from folate

Question 17

methionine adenosyl transferase

Answer 17

synthesizes SAM from ATP and methionine

Question 18

What is cobalamin/B12 used for

Answer 18

regeneration of methionine from homocystein

Question 19

what are the three pathways for glycine degradation?

Answer 19

1. cleaved to CO2 and NH4 by glycine cleavage enzyme. NAD gets the H+ and uses THF as a cofactor
2. glycine to serine using THF, pyridoxal phosphate. enzyme is serine hydroxymethyltransferase
3. oxidation to glyoxylate to oxalate using NAD

Question 20

What can be made from threonine?

Answer 20

2-amino-3-ketobutyrate yields glycine and acetyl CoA (ketogenic)
or
degraded to succinyl CoA (glucogenic)

Question 21

What are the histidine products? Cofactors?

Answer 21

glutamate and alpha-ketogluterate

Question 22

draw linkage between the cofactors and the sam cycle

Answer 22

see attached

Question 23

homocysteinuria. other causes?

Answer 23

problems with the enzyme cystathionine synthase. build up of homocystein, which is excreted into the urine.
leads to thromboembolic events, lens dislocation, mental retardation, and osteoporosis. treated with a low met diet
other possible cause: difficulty with MTHFR (enzyme that turns homocystein into methionine)

Question 24

what happens when ammonia is allowed to accumulate in the brain, biochemically

Answer 24

there is a depletion of glutamate and an increase in glutamine. without glutamate, the brain also doesn’t have enough of the neurotransmitter GABA
leads to osmotic swelling, coma, lethargy, and death

Question 25

what is the alanine/glucose cycle?

Answer 25

between skeletal muscle and liver
proteins break down into amino acids and ammonia. ammonia added to alpha-ketoglurate to form glutamate. combine with pyruvate to form alanine and alphaketogluterate via alanine aminotransferase (ALT). alanine goes thru blood to liver, where it is digested to pyruvate and glutamate. glutamate forms urea, pyurvate becomes glucose, and glucose returns to blood.

Question 26

glutaminase

Answer 26

releases ammonia from glutamine in the liver

Question 27

draw urea cycle

Answer 27

see attached

Question 28

what are three drugs used to treat urea cycle disorders?

Answer 28

sodium benzoate, phenylbutyrate and phenylacetate. act as a nitrogen sink and can be excreted by the kidneys

Question 29

What is the one X-linked urea cycle disorder?

Answer 29

OTC deficiency

Question 30

N-acetylglutamate synthetase

Answer 30

enzyme that convers glutamate and acetyl CoA to N-acetylglutamate. N acetylglutamate increases the activity of CPS-I.
Arginine increases the activity of Nacetylglutamate

Question 31

What enzyme deficiency causes maple syrup urine disease?

Answer 31

ketoacid dehydrogenase that converts the keto acids of Val, Iso, and Leu into various CoA things

Question 32

What cofactor is associated with ketoacid dehydrogenase

Answer 32

thiamine

Question 33

What is the pathway for propinoyl CoA

Answer 33

comes from isobutryl CoA and 2 methylbutryl CoA (from Val and Iso. respectively)
goes to methylmalonyl CoA to succinate

Question 34

propinoic acidemia

Answer 34

VOMIT: valine, odd chain fatty acids, methionine, isoleucine, and threonine
deficiency in propinoyl CoA carboxylase- cant get from propinoyl CoA to methylmalonyl CoA
failure to thrive, vomiting, resp. distress, anion gap metabolic acidosis, hypoglycemia, hyperammonimia. may be helped with biotin

Question 35

propionyl CoA carboxylase

Answer 35

enzyme which converts propionyl CoA into methylmalonyl CoA. When deficient, causes propinoic acidemia

Question 36

when does biotin convert holoenzymes into apoenzymes?

Answer 36

propinyl CoA carboxylase, pyruvate carbxylase, 2-methylcrotonyl CoA carboxylase, because these enzymes are biotinylated by holocarboxylase synthetase

Question 37

biotinidase

Answer 37

the enzyme that elps recycle biotin. without it, you must supplement biotin or you see multiple carboxylase deficiency