Protein Biochemistry 2

Question 1

5 major reactions of the urea cycle

Answer 1

1. NH3 + CO2 + 2ATP (carbamoyl phosphate synthetase 1) –> carbamoyl phosphate
2. Ornithine + carbamoyl phosphate (ornithine transcarboxylase) –> cirtrulline
3. Cirtrulline + Aspartate (argininosuccinate synthase) –> argininosuccinate
4. Argininosuccinate (argininosuccinase) –> arginine
5. arginine (arginase) –> ornithine + urea

Question 2

Location of carbamoyl phosphate synethetase I

Answer 2

mitochondria

Question 3

Cofactors for function of carbamoyl phosphate synthetase I

Answer 3

arginine activates N-acetylglutamate synthase –> acetyl CoA + glutamate –> N-acetylglutamate –> allosteric activation of carbamoyl phosphate synthetase I

Question 4

important reaction catalyzed by carbamoyl phosphate synthetase I

Answer 4

bicarb + ammonia –> carbamoyl phosphate

uses 2 of the 3 ATPs in the urea cycle

Question 5

how is ammonia transported through the blood

Answer 5

glutamine “holds” 2 ammonia groups

synthesized from glutamate by glutamine synthetase –> takes N to liver –> NH3 release via glutaminase –> urea cycle

Question 6

function of glutamate dehydrogenase

Answer 6

control point for protein metabolism in mitochondria. controls direction of either N removal or incorporation into amino acids

activators: ADP, GDP
inhibitors: ATP, GTP

Question 7

Transport of ammonia in muscle

Answer 7

uses alanine (converted from pyruvate) instead of glutamine (alanine-glucose cycle) for transport to the liver. liver uses alanine to convert back to pyruvate (transamination), and glucose is remade via gluconeogenesis to be delivered back to the muscle

Question 8

glucogenic amino acid breakdown

Answer 8

produces pyruvate or Kreb cycle intermediates

Ex: aspartate transamination –> oxaloacetate

Question 9

ketogenic amino acid breakdown

Answer 9

no net production of glucose

Ex: lysine and leucine –> acetyle CoA

lysine and leucine are the only ketogenic amino acids

Question 10

Examples of branched chain amino acids

Answer 10

leucine, valine, isoleucine

Question 11

decarboxylation of branched chain amino acids

Answer 11

the three amino acids are deaminated (branched-chain aminotransferase –> a-keto acids

decarboxylated by branched-chain a-ketoacid dehydrogenase complex –> isovaleryl CoA (leucine), Isobutyryl CoA (valine), a-methyl-butyryl CoA (isoleucine)

Question 12

Maple Syrup Urine Disease

Answer 12

deficiency of branched-chain a-ketoacid dehydrogenase complex –> buildup of a-keto acids in urine –> sweet smelling

Question 13

Role of tyrosine in thyroid chemistry

Answer 13

used to make T4 (prohormone) –> T3 (hormone)

Question 14

mechanism of thyroid hormone release

Answer 14

TSH –> iodide uptake and release of T4/T3

Question 15

Function of thyroid peroxidase

Answer 15

oxidizes iodide (I-) to iodine (I2), which eventually end up bound to T3/T4

Question 16

function of thyroglobulin

Answer 16

contains Tyr residues iodinated to form T4/T3

Question 17

How is T4/T3 transported?

Answer 17

via thyroxin binding globulin (TBG)

Question 18

Where are porphyrins produced?

Answer 18

liver

Question 19

Reactions for porphyrin production

Answer 19

1. Gly + succinyl CoA + (delta-aminolevulinate synthase, mitochondria) –> delta-aminolevulinic acid (ALA)
2. 2xALA (delta-aminolevulinate dehydratase, cytosol) –> porphobilinogen
3. Porphobilinogen –> –> –> –> protoporphyrin IV
4. Protoporphyrin IX (ferrochelatase) –> heme

Question 20

Porphyria

Answer 20

general term for diseases in porphyrin synthesis

Question 21

mechanism of lead poisoning

Answer 21

inhibits delta-aminolevulinate dehydratase and ferrochelatase

Question 22

Process of porphyrin (heme) degradation

Answer 22

heme –> biliverdin –> bilirubin –> bilirubin diglucuronide –> urobilinogen –> stercobilin

Question 23

how is bilirubin transported in blood?

Answer 23

via albumin

Question 24

function of ORNT1 in the urea cycle

Answer 24

transport ornithine in and cirtulline out of the mitochondria

Question 25

regulation of carbamoyl phosphate synthetase 1

Answer 25

N-acetylglutamate = activator

acetyl CoA + Glu (N-acetylglutamate synthase) –> N acetylglutamate

N-acetylglutamate synthase = activated by arginine

Question 26

important derivatives of arginine

Answer 26

NO (produced via NO synthase, which also creates citrulline to go through the urea cycle)

Creatine phosphate (high energy storage molecule) and ornithine