Amino acid Metabolism

Question 1

Amino acids for energy

Answer 1

1. Normal protein turnover
   - catabolized to energy of not required for synthesis of proteins
2. High protein diet
   - excess amino acids
   - can not be stored
3. Starvation
   - no carbohydrates, fats
   - body catabolizes cellular protein, mostly from muscle

Question 2

Location of dietary protein breakdown

Answer 2

mainly in liver

Question 3

Dietary protein to stomach

Answer 3

stimulate G cells to secrete gastrin

Question 4

Role of gastrin

Answer 4

stimulates chief cells- pepsinogen

parietal cells - HCL

Question 5

Role of HCl in breakdown

Answer 5

kill bacteria/foreign particles
denature dietary proteins
stimulate pepsinogen - pepsin

Question 6

Role of pepsin

Answer 6

catalyses the breakdown of polypeptide to many smaller pieces

Question 7

Peptides to duodenum

Answer 7

stimulate duodenum - secretin + CCK

Question 8

Role of secretin

Answer 8

stimulate release of HCO3- from pancreas - pH to normal

Question 9

Role of CCK

Answer 9

stimulates exocrie pancreas to release zymogens:
trypsinogen - ENETROPEPTIDASE - trypsin
chymotrypsinogen - TRYPSIN - chymotrypsin
proelastase - TRYPSIN - elastase
procarboxypeptidases - TRYPSIN - carboxypeptidase

Question 10

Role of proteases

Answer 10

cleave peptides smaller

Question 11

Role of peptidases

Answer 11

Carboxypeptidase - remove COO- terminal AAs

Aminopeptidase - remove NH2 terminal AAs

Question 12

Transport of AAs

Answer 12

gluthatione ( gamma-glutamyl cycle)

Question 13

Protein turnover

Answer 13

external: collagenases, metalloproteases, elastases
internal: catepsins, ubiquination

Question 14

Transamination reaction

Answer 14

alpha-AA + alpha-ketogluatarate -> alpha-ketoacid + glutamate

enzyme: Aminotransferase
coenzyme: PLP

Question 15

Pyridoxal phosphate PLP

Answer 15

from vitamin B6
cofactor in all reactions concerning aminotransferases
bound to Lys residue of enzyme as Schiff base
grabs NH4+ from AA and gives it to KG
PLP -> pyridoxamine phosphate -> PLP

Question 16

ALAT and ASAT

Answer 16

ALAT (alanine aminotransferase): in liver
ASAT(aspartate aminotransferase): heart/muscle
non-functional plasma enzymes
markers of tissue damage

Question 17

Glutamate Dehydrogenase

Answer 17

Glu + H2O + NAD+ -> alpha-KG + NH4 + NADH
NH4 goes to urea cycle
alpha-KG to TCA

Question 18

Allosteric regulation of Glutamate DH

Answer 18

activated by ADP

inhibited by GTP

Question 19

Isoenzymes of Glutamate DH

Answer 19

GLUD1: liver, kidney etc.
GLUD2: brain, testis

Question 20

Glutamine synthase

Answer 20

in extrahepatic tissue
NH4 attached to Glu -> Gln
transported to liver, kidney

Question 21

Glu -> Gln

Answer 21

Glu + ATP -> gamma-glutamyl P + ADP.. +NH3 -> Gln + Pi

enzyme: glutamine synthase

Question 22

Glutaminase

Answer 22

in liver mitochondria
Gln -> Glu
+H20
-NH4 (to urea cycle)

Question 23

Glucose- Alanine cycle

Answer 23

glucose - pyruvate - alanine - pyruvate -glucose
enzyme: alanine aminotransferase ALAT
NH4+ from muscle transported to liver

Question 24

Deamination

Answer 24

1. Oxidative deamination
   - Glu DH
2. Catabolism
   - Ser (Thr) dehydratase
   - His + Gly
3. Flavoproteins
   - L-AA oxidase
   - D-AA oxidase
4. Loss of beta/gamma amide
   - glutaminase
   - asparginase
5. Nucleotide metabolism

Question 25

Incorporation of free ammonia

Answer 25

1. Glu DH - at high ammonia conc.
2. Carbamyl-P synthetase- urea cycle
3. Gln synthetase