0221 Protein degradation and disposal of nitrogen

Question 1

What are some roles/functions of protein in the body

Answer 1

hormones (bio-signalling), body protein, ketone bodies, Acetyl CoA, Urea

Question 2

What is the general name of a reaction where a NH3 is removed from a compound but not transferred to another. Give an example

Answer 2

Oxidative deanimation. Alanine deanimates to pyruvate

Question 3

What is metabolic funneling of proteins and give examples of end products

Answer 3

Metabolic funneling is the concentration of amino acid flux into a few key compounds through amino-transferases. Some of these end products are: glutamate (from alpha-keto-glutarate), Aspartate (from oxaloacetate), Alanine (from pyruvate)

Question 4

What product do most amino acid flux from peripheral tissues funnel to

Answer 4

Glutamate

Question 5

What is the enzyme that catalyzes glutamine formation from glutamate and NH3? What is the role of glutamine and where does it travel to

Answer 5

The enzyme is glutamine synthase. Glutamine transports 2 NH3 groups to the liver as it is non-toxic and can be in high concentrations in the blood

Question 6

Where does alanine go to from the muscles and what is it’s role

Answer 6

Alanine (from pyruvate) is transported to the liver where it can be used in gluconeogenesis

Question 7

What is the enzyme responsible for the oxidative deanimation of glutamate? Where does this deanimation occur

Answer 7

Glutamate dehydrogenase. Oxidative deanimation of glutamate occurs in the liver and kidneys

Question 8

What is the structure of urea

Answer 8

2 NH2 attached to a central carbon which is also double bonded to an oxygen

Question 9

How does NH3 get commited into the urea cycle? What is the enzyme that catalyses this reaction and where does urea enter the urea cycle?

Answer 9

Urea enters the urea cycle as carbamoyl-phosphate (produced via carbamoyl-phosphate synthase). It enters the urea cycle in the mitochondrial matrix

Question 10

How is entry of Carbamoyl-phosphate into the urea cycle regulated

Answer 10

Allosteric regulation by NAG (N-actylglutamate) which stimulates the process

Question 11

What are the 2 entry points to the urea cycle and what are the 2 products? Where do these compounds enter/leave the urea cycle (relative to the cell)

Answer 11

Entry points: carbamoyl phosphate (matrix) and aspartate (cytosol). Products: fumarate (cytosol) and urea (cytosol)

Question 12

What is the product of Alpha-keto-glutarate + amine group

Answer 12

Glutamate

Question 13

What is the product of Oxaloacetate + amine group

Answer 13

Aspartate

Question 14

What is the product of pyruvate + amine group

Answer 14

Alanine

Question 15

Where does glutamate primarily come from (think tissues) and what is its role once it reaches the liver

Answer 15

Glutamate primarily comes from the peripheral tissues and is excreted in urea (via oxidative deanimation) once in the liver

Question 16

Where does alanine primarily come from (think tissues) and what is its role once it reaches the liver

Answer 16

Alanine primarily comes from muscles and is recycled via gluconeogenesis once it reaches the liver

Question 17

What is the major oxidative deamination enzyme in humans (hint: what is the major amino in the body)

Answer 17

Glutamate dehydrogenase is the major oxidative deamination enzyme

Question 18

Where is nitrogren primarily released from amino acids (oxidative deamination)

Answer 18

Oxidative deamination primarily occurs in the liver and kidneys

Question 19

What are the 2 fates of ammonium in the body

Answer 19

1. Conversion to urea for excretion (main). 2. Excretion via kidneys (secondary)

Question 20

What is the commited step of nitrogen to the urea cycle

Answer 20

C02+NH3 = carbamoyl-phosphate (Carbamoyl phosphate synthase)

Question 21

Describe regulation of the urea cycle by NAG (N-acetylglutamate)

Answer 21

Increased [glutamate] in body = increased amino acid flux and [NAG} (formed by glutamate and acetyl-CoA). Increased NAG stimulates the urea cycle, increasing nitrogen excretion

Question 22

Where in the cell does the urea cycle occur

Answer 22

In both the mitochondrial matrix and the cytosol