Final: nitrogen and urea cycle

Question 1

what waste can’t the kidney deal with on its own?

Answer 1

ammonia

the liver must step in

Question 2

where does urea cycle occur?

Answer 2

in the mitochondria

so it doesn’t affect cytoplasm by being toxic

Question 3

urea cycle overview

Answer 3

modify chemical structure of substrates to create urea

Question 4

urea cycle: where does it occur

Answer 4

first 2 steps in mitochondria, rest of the steps in the cytosol

Question 5

urea cycle rxn 1

Answer 5

2 ATP, bicarbonate, and ammonia become carbamoyl phosphate

enzyme: carbamoyl phosphate synthetase 1 (CPS1)

Question 6

carbamoyl phosphate

Answer 6

carb = carboxyl group from CO2
amoyl = nitrogen group from ammonia
phosphate = phosphate group from 1 of ATP

Question 7

CPS1 regulation

Answer 7

N-acetylglutamate allosterically activates CPS1
modifies physical shape of CPS1 so it processes ammonia more efficiently
increases urea synthesis

Question 8

how is N-acetylglutamate made?

Answer 8

made by mitochondrial enzyme: N-acetylglutamate synthetase combines glutamate and acetyl-CoA to make N-acetylglutamate

Question 9

low N-acetylglutamate levels

Answer 9

CPS1 has very low affinity for ammonia, ammonia can build up to toxic levels

Question 10

what organic linkage buffers ammonia within cells?

Answer 10

glutamic acid

Question 11

2 functions of urea cycle

Answer 11

1) waste disposal

2) synthesis of Arginine

Question 12

CPS1 location and function

Answer 12

in mitochondria
3 enzyme activities connected
2 ATP, bicarbonate, ammonia –> first intermediate of urea cycle

Question 13

high glutamate concentration =

Answer 13

more N-acetyl-glutamate = more CPS1 = more urea cycle flux

Question 14

urea cycle regulation is based on…

Answer 14

NEED (amount of protein in diet), not hormones