Protein Production

Question 1

Name three classes of protein that the liver produces.

Answer 1

Plasma proteins
Clotting factors
Complement factors

Question 2

Name the most abundant plasma protein.

Answer 2

Albumin

Question 3

How does albumin maintain colloid osmotic pressure?

Answer 3

Albumin in the plasma means that the water concentration of the blood plasma is lower than that of the interstitial fluid, meaning there is a net flow of water out of the interstitial fluid into the blood plasma.

Question 4

Describe the Starling forces.

Answer 4

1. Capillary hydrostatic pressure (favours fluid movement of the capillary)
2. Interstitial hydrostatic pressure (favours fluid movement into the capillary)
3. Osmotic force due to plasma protein concentration (favours fluid movement into the capillary)
4. Osmotic force due to intestinal fluid protein concentration (favours fluid movement out the capillary)

Question 5

Describe the work of Starling forces at the arterial end of the capillary.

Answer 5

Arterial end of capillaries has a greater hydrostatic pressure than that of the interstitial fluid. However, capillary also has a higher oncotic pressure than the interstitial fluid as it contains more plasma proteins. Overall, the hydrostatic pressure is greater than the oncotic pressure, so the net movement of water is out of the capillary into the interstitial fluid.

Question 6

Describe the work of Starling forces at the venous end of the capillary.

Answer 6

Capillary hydrostatic pressure has declined due to the resistance to blood flow generated by the capillary. The net inward pressure exceeds that of the net outward pressure so the bulk of the fluid moves into the capillary.

Question 7

How does liver failure lead to oedema?

Answer 7

Liver failure leads to reduction in albumin. Reduction in album reduces capillary oncotic pressure. This causes accumulation of water in the interstitial fluid, causing oedema.

Hypoalbuminaemia = oedema

Question 8

What function do globulins have?

Answer 8

Antibody function.

Question 9

Which types of globulin are made in the liver?

Answer 9

Alpha + Beta.

Question 10

Which clotting factors does the liver produce?

Answer 10

All, except calcium IV and von Willebrand factor

Question 11

What is a complement factor?

Answer 11

A plasma protein which sticks to pathogens and is recognised by neutrophils - acts as a marker.

Question 12

Which term refers to the continuous degradation and re-synthesis of all cellular proteins?

Answer 12

Protein turnover

Question 13

What does an increase in protein turnover indicate?

Answer 13

Increase is seen when tissues are undergoing structural re-arrangement e.g. when tissue is damaged via pregnancy, severe burns, skeletal muscle in starvation

Question 14

Name the two primary methods of protein breakdown.

Answer 14

Lysosomal and Ubiquitin-proteasome pathway

Question 15

Describe lysosomal protein breakdown.

Answer 15

Carried out in liver.

1. Sinusoidal endothelial cells remove soluble proteins and fragments from the blood through sieve plates
2. Kupffer cells phagocytose particulates and package them into phagosomes containing hydrolytic enzymes which will break down the protein into amino acids

Question 16

Describe Ubiquitin-Proteasome protein breakdown.

Answer 16

In this pathway, degradation is a selective process.

1. Proteins are targeted by the attachment of ubiquitin to the protein
2. Ubiquitin directs the protein to a protein complex called proteasome which unfolds the protein and breaks it down into small peptides

Question 17

In amino acid catabolism (break down), which group must be removed?

Answer 17

The alpha amino group. Produces nitrogen and a carbon skeleton.

Question 18

Name the two main amino acid catabolism processes.

Answer 18

Oxidative deamination

Transamination

Question 19

Which amino acid is the only one that undergoes rapid oxidative deamination?

Answer 19

Glutamate

Question 20

Describe oxidative deamination.

Answer 20

Amino acid + water = A keto acid and ammonia. Ammonia is converted to urea in the urea cycle as it is toxic.

Question 21

Describe transamination.

Answer 21

This is the transfer of an alpha-amino group from an amino acid to a keto-acid. Forms an alpha-keto-acid.

Question 22

If alanine undergoes transamination, which products are formed?

Answer 22

Pyruvate and glutamate

Question 23

Which enzyme is needed for transamination?

Answer 23

Aminotransferase - found in cytosol of mitochondria.

Each aminotransferase is specific to one amino group.