1: Physiology: Urea Cycle class notes

Question 1

Where does the urea cycle occur?

Answer 1

in the liver

Question 2

What is Urea?

Answer 2

is a non-toxic nitrogenous compound derived largely from the amino groups of amino acids, the carbon skeletons of which are put to other uses (such as oxidation and gluconeogenesis)

Question 3

How is the amino group removed from the amino acids?

Answer 3

achieved through deamination (in which case a free NH3 is generated) which is preformed by deaminases
and transamination  (in which case the amino group is transferred from the amino acid  an amino group acceptor), preformed by transaminases.

Question 4

What are the two most important transaminases?

Answer 4

alanine transaminase (ALT) which transfers the amino group form the alanine to the alpha ketoglutarate, thereby forming pyruvate (for oxidation or gluconeogenesis) and glutamate 
aspartate transaminase (AST) which transfers the amino grouo from glutamate to oxaloacetate, thereby forming aspartate and regenerating alpha ketoglutarate.

Question 5

Alpha ketoglutarate is also regenerated how?

Answer 5

via oxidation/deamination of glutamate.

the free NH3 is organified into carbamoyl phosphate.

Question 6

What do carbamoyl phosphate and aspartate do?

Answer 6

they are the molecules that deliver the amino group to the urea cycle.

Question 7

Urea synthesis is?

Answer 7

energetically expensive (note the use of ATP)

Question 8

What cells produce Urea?

Answer 8

in cytoplasm of liver cells

Question 9

If the liver is sick, what happens to urea production?

Answer 9

urea production decreases

Question 10

Urea is used how?

Answer 10

use by the body on its way out as a WASTE product

Question 11

What does the Urea Cycle require?

Answer 11

enzymes found in the mitochondria and in the cytoplasm