Protein metabolism

Question 1

Principal site of amino acid metabolism

Answer 1

the liver

Question 2

Summary of protein digestion in the body

Answer 2

1.Mouth - saliva no effect
2.Stomach - HCI secreted -denatures protein
Pepsin secreted - hydrolyses peptide bonds (only 10%)

Large polypeptides enter

3. small intestine - Trypsin, chymotrypsin, carboxypeptidase and aminopeptidase enzymes hydrolyse peptide bonds therefore break the peptide bonds and provide individual amino acids
4. intestinal lining - amino acids absorbed by active transport via intestinal wall into the bloodstream

Question 3

Amino acids produced from protein digestion enter the amino acid pool ( total supply of free amino acids to be used by the body) - Where is the amino acid pool derived from?

Answer 3

Dietary protein
Protein turnover
Biosynthesis of non essential amino acids in the liver

Question 4

There is no specialised storage of amino acids in the body therefore

Answer 4

a constant source of amino acids is needed to maintain normal metabolism

Question 5

The body is in a state of nitrogen balance when

Answer 5

amount of nitrogen taken in (protein) equals the amount of nitrogen excreted from the body in waste materials (urea)

Question 6

Possible fates for amino acid degradation products

Answer 6

Amino acid > degradation >

Carbon portion (carbon skeleton) broken down in central metabolic pathway - CAC/ETC/OP - used for energy production.

Nitrogen ( NH2) portion eliminated by urea, biosynthesis of non essential amino acids or

Question 7

each of 20 amino acids has a different carbon skeleton therefore

Answer 7

Each carbon skeleton undergoes a different degradation pathway which will form one of the 7 degradation products

• Pyruvate
• Acetyl CoA
• Acetoacetyl CoA
• intermediates of CAC - a-ketogultarate, succinyl CoA, Fumarate and Oxaloacetate

Question 8

Transamination

Answer 8

degradation of amino acids in the liver, usually produces glutamate and a new a-keto acid

Catalysed by Transaminase

Question 9

Oxidative deamination

Answer 9

Removes the amino group (Nitrogen portion ) from the amino acid (carbon skeleton)

Question 10

1. Transamination generally involves

Answer 10

α-ketoglutarate being converted to glutamate at the same time as another amino acid is converted to its related α-ketoacid

Question 11

Urea cycle occurs in the

Answer 11

cytoplasm and mitochondria

Question 12

Glucogenic amino acids provide

Answer 12

carbon atoms for glucose production

Question 13

Ketogenic amino acids provide

Answer 13

provide carbon atoms for acetyl Co A prodcuction

Question 14

where does the Urea cycle occur

Answer 14

liver - mitochondria and cytoplasm

Question 15

Why is the urea cycle important ?

Answer 15

synthesis of urea in the liver is the main way of removal of NH4+

Defect in any of the 4 steps of the urea cycle can lead to devastating consequences

Question 16

Brief overview of stages producing Urea

Answer 16

Amino acids undergo transamination to keto acids and glutamate. Glutamate is deaminated by removing the amino group (oxidative deamination by glutamate dehydrogenase). The amino group is converted to ammonium ion (NH4+) & then to urea in the urea cycle.

Question 17

1. What is the end product of protein catabolism?

Answer 17

ammonium ion