Protein Metabolsim

Question 1

When proteins are broken down what is the process called?

Answer 1

Proteolysis

Question 2

Briefly describe how protein is used to provide energy?

Answer 2

Depending on the side chains of an amino acid they will either be classified as glucogenic amino acids which can go through the process of gluconeogenesis or classed as ketogenic and will be used to produce ketone bodies, either way both result in energy.

There is also the amino groups to think about. This is converted quickly into urea which is then excreted in urine and does not play a role in energy production

Question 3

Depending on whether an amino acid is glucogenic or ketogenic or both they will have different metabolic pathways, give an example of a pathway for each type.

Answer 3

Ketogenic: lysine
Converted to acetyl CoA and enters the kreb cycle

Glucogenic: alanine
Converted to pyruvate, converted to acetyl CoA and enters the kreb cycle

Both: phenylalanine
Converted to acetyl CoA and enters the the kreb cycle

Question 4

In what situation is protein broken down to provide energy?

Answer 4

During extreme stress (starvation)

It is something that occurs under hormonal control

Question 5

What effect does insulin and growth hormone have on protein synthesis and degradation?

Answer 5

Increase synthesis

Decreases degradation

Question 6

What effect does glucocorticoids (eg cortisol) have on protein synthesis and degradation?

Answer 6

Decreases synthesis

Increases degradation

Question 7

Excessive breakdown of protein can occur in Cushing’s syndrome, why does this happen and what effect does this have superficially?

Answer 7

Cushing’ is a syndrome where there is excess cortisol which promotes protein degradation. This weakens the skins structure leading to a striae formation. (Looks a little like stretch marks)

Question 8

Some aminoacids can be synthesised in the body. Where do the carbon atoms come from?

Answer 8

Intermediates of glycolysis (C3)

Pentose phosphate pathway (C4/5)

Krebs cycle (C4/5)

Question 9

Where are the amino groups from that go into making new amino acids?

Answer 9

From other amino acids-transamination

Or from ammonia

Question 10

What are the two ways in which the nitrogen is removed from the amino acids?

Answer 10

Transamination-swapping the amine group with an oxygen of a keto acid.

Deamination- liberates amino group as free ammonia

Question 11

Why is transamination sometimes beneficial?

Answer 11

It produces a better amino acid that can be dealt with more easily

Question 12

What does alanine aminotranferase do?

Answer 12

ALT

Converts alanine to glutamate

Question 13

What does aspartate aminotranferase do?

Answer 13

Converts glutamate to aspartate

Question 14

How can plasma levels of ALT and AST be used?

Answer 14

They can indicate liver function

Question 15

Levels of ALT and AST are particularly in high in condition where there is excessive cellular necrosis, give 3 examples of conditions in which this occurs?

Answer 15

Viral hep

Autoimmune liver disease

Toxic injury

Question 16

Why does deamination occur in the liver and kidneys?

Answer 16

So that the ammonia can be dealt with straight away because it is very toxic

Question 17

Why is deamination needed for dietary D-amino acids?

Answer 17

Because it cannot be metabolised in the form it is in. We need to deaminate it straight away

Question 18

How is the urea cycle and transamination linked?

Answer 18

The glutamate and aspartate amino acids produced in transamination can be readily fed into the urea cycle which helps the body to convert the ammonia into urea

Question 19

What is the purpose of the urea cycle?

Answer 19

It is a way of safely excreting amino acids.

The ammonia produced from deamination is used in the cycle and the glutamate and aspartate created in transamination can also be used.

Question 20

The urea cycle occurs in the liver and is controlled by 5 enzymes. What does the amount of enzyme correlate to?

Answer 20

The need to dispose of ammonia

Ie lots of ammonia=lots of enzyme

High protein diet induces enzyme levels

And low protein diet/ starvation represses levels

**cycle is inducible but not regulated

Question 21

What is the danger with refeeding syndrome?

Answer 21

The lack of protein has led to the down regulation of the enzymes needed for the urea cycle.

So giving lots of protein will overwhelm the liver and there is a risk of ammonia toxicity occurring

Question 22

Genetic disorders and mutation can cause the complete lack and/or the partial loss of an enzyme in the urea cycle. What can this lead to? (2)

Answer 22

Hyperammonaemia

Accumulation/excretion of urea cycle intermediates

Question 23

How can amino acids be used as fuel sources?

Answer 23

Converted to glucose or ketone bodies