protein metabolism

Question 1

How is amino acid transported and stored?

Answer 1

Amino acid = breakdown product of protein metabolism
- it needs active or carrier facilitated transport to get into the cells
- once inside, immediately conjugated to form proteins again, and is stored as protein
- when plasma amino acid concentration is low, the protein can be quickly broken down again to transport out of the cell
- if there is a lack of protein, intracellular protein will be degraded to supply proteins
- if there is excessive amino acids and the cells have reached protein storage capacity, it’s used as energy, or converted to glycogen or fat and stored

Question 2

What are the 3 major proteins found in plasma and their function?

Answer 2

1. albumin, to maintain oncotic pressure
2. fibrinogen, important in coagulation
3. globulin, immune function

All but globulin are mainly formed in the liver and the liver is capable of rapid protein production.

Question 3

What the does synthesis of non-essential amino acid depend on?

Answer 3

formation of the appropriate alpha-keto acid precursor for the respective amino acid.
Ex. Pyruvic acid, breakdown of glycolysis, is the precursor for alanine

Question 4

How is protein used for energy?

Answer 4

• mostly happens in the liver
• deamination –> removes an amino group –> generates specific keto acid that can go into the citric acid cycle
• the resultant amount of APT produced per gram of protein is slightly less than for glucose.

Question 5

What’s a waste production of demamination?

Answer 5

ammonia, it’s converted to urea by the liver

Question 6

What’s obligatory protein loss?

Answer 6

if there is no protein in the diet, a certain amount of protein of the body will still be degraded to supply amino acids

Question 7

How does growth hormone regulate protein metabolism?

Answer 7

growth hormone enhances transport of amino acid through cell membranes and accelerates DNA/ RNA transcription and translation of protein
- it also increased fat liberation form fat depots

Question 8

How does insulin effect protein metabolism?

Answer 8

helps to accelerate amino acid transport into cells
- lack of insulin = almost no protein synthesis

Question 9

How does glucocorticoids influence protein metabolism?

Answer 9

it increases the rate of breakdown of extrahepatic protein
- esp important in promoting ketogenesis and gluconeogenesis

Question 10

How does testosterone regulate protein metabolism?

Answer 10

testosterone increases protein deposition in the body, esp in muscles
- cause enlargement for several months (unlike GH, which is indefinite)

Question 11

How does thyroxine regulate protein metabolims?

Answer 11

Thyroxine increases metabolism, which indirectly affects protein metabolism.
- if there isn’t enough carbohydrate or fats, then protein will be rapidly degraded for energy
- if there is adequate amount of carbohydrate/ fats for energy, then the excess amino acids are used to increase the rate of protein synthesis
- lack of thyroxine = greatly delayed growth due to lack of protein synthesis