Lecture 21: PPP, AAs, Urea Cycle

Question 1

What is the purpose of the PPP?

Answer 1

1. Generate NADPH reducing equivalents for biosynthetic reactions
2. Generate pentoses for DNA, RNA, A/G/C/UTP, CoA, FAD, NAD, etc. synthesis

Question 2

G6P deficiency

Answer 2

Most common human enzyme defect; deficient PPP. Neonatal jaundice, acute hemolytic anemia; low NADPH -> low reduced GSH -> less resist. to lipid peroxidation

Question 3

AAs as NTs and signaling agents

Answer 3

Direct NTs: glycine, glutamate
Tyr -> thyroid hormone, melanins, epi, NE, dopamine
GABA from Glu
His -> histamine
Trp -> serotonin
Arg -> NO

Question 4

Proteolytic signals

Answer 4

Ubiquitin, oxidation of particular residues, PEST seq. regions (Pro, Glu, Ser, Thr), N-terminal residues

Question 5

Where does the urea cycle occur?

Answer 5

In the liver only

Question 6

How is the urea cycle primarily regulated?

Answer 6

Carbamoyl-P synthetase 1 is activated by acetyl-Glu, signaling increased NH3

Question 7

Urea cycle adaptive behavior

Answer 7

Enzymes increase with high protein diets and starvation

Question 8

What is the function of the alanine cycle with the urea cycle?

Answer 8

The Ala cycle helps transport excess amino groups to the liver from muscle

Question 9

Hyperammonemia

Answer 9

High blood ammonia due to urea cycle deficiency; highly neurotoxic

Question 10

Phenylketonuria

Answer 10

Phenylalanine hydroxylase deficiency, leading to buildup of Phe which is neurotoxic. Normally makes Tyr

Question 11

MSUD

Answer 11

Branched chain aminotransferase deficiency

Question 12

Albinism

Answer 12

Tyr normally makes melanin

Question 13

Alcapturia

Answer 13

Homogentisate oxidase deficiency results in black urine