Protein + Amino Acid Metabolism

Question 1

Name four major N containing compounds

Answer 1

Amino acids
Proteins
Purine + Pyrimidines (RNA/DNA)
Creatine phosphate

Question 2

What is the breakdown product of creatine and creatine phosphate?

Answer 2

Creatinine

Question 3

Where is creatine and creatine phosphate broken down?

Answer 3

The muscle

Question 4

What is the creatinine excretion in the urine proportional to?

Answer 4

Muscle mass

Question 5

What is creatinine excretion in the urine also an indicator of?

Answer 5

Renal function

Question 6

What does a positive N balance mean?
What does it indicate about body protein?
When does it occur?

Answer 6

Intake>output
Increase in total body protein
Growth, pregnancy, recovering from malnutrition

Question 7

What does a negative N balance mean?
What does it indicate about body protein?
When does it occur?

Answer 7

Intake<output
Net loss of body protein
Not normal - trauma, infection, malnutrition

Question 8

When does mobilisation of protein reserves occur?

Answer 8

Extreme stress - starvation

Question 9

What is the mobilisation of protein reserves controlled by?
Give three examples

Answer 9

Hormones

Insulin, growth hormones, glucocorticoids

Question 10

Which hormones increase protein synthesis and decrease protein degradation?
Vice versa

Answer 10

Insulin and growth hormones

Glucocorticoids

Question 11

What is the syndrome that there is excessive breakdown of proteins?

Answer 11

Cushing’s syndrome

Question 12

What is formed in Cushing’s syndrome?

Answer 12

Striae

Question 13

What does it mean when amino acids are conditionally essential?

Answer 13

Can synthesise but may need to consume when demands increase

Question 14

Where do C atoms come from for amino acid synthesis?

Answer 14

Glycolysis
Pentose phosphate pathway
Krebs cycle

Question 15

Where can an amino group be sourced by other amino acids? (2)

Answer 15

Transamination - transfer of an amino acid from one molecule to another

From ammonia

Question 16

What are the two things that could happen to N once removed?

Answer 16

Incorporated into other compounds
Excreted as urea

Question 17

What are the two main pathways that facilitate the removal of N from amino acids?

Answer 17

Transamination
Delaminating

Question 18

Why does an amine group sometimes need to be removed from an amino acid?

Answer 18

So the C skeleton can be used to give energy

Question 19

Why does amine need to be excreted?

Answer 19

Otherwise it will produce ammonia

Question 20

Describe Transamination

Answer 20

Amine group swapped for a keto group

Question 21

What enzyme is used is Transamination?

Answer 21

Aminotransferase

Question 22

What do aminotransferase enzymes used to funnel an amino group to glutamate?

Answer 22

Alpha ketoglutarate

Question 23

What do aminotransferases require?
What is it derived from?

Answer 23

Coenzyme pyridoxal phosphate
Vitamin B

Question 24

Name two key aminotransferases

Answer 24

ALT - alanine aminotransferase
AST - aspartate aminotransferase

Question 25

What does plasma ALT and AST levels show?

Answer 25

Liver function

Question 26

What does ALT do?

Answer 26

Catalyses inter conversion of alanine and alpha-ketogluratate to pyruvate and glutamate

Question 27

What does AST do?

Answer 27

Catalyses inter conversion of aspartate and alpha-ketoglutarate to oxaloacetate and glutamate

Question 28

What occurs in deamination? Where does it occur?

Answer 28

Liberates amino group as free ammonia Liver and kidneys

Question 29

Why is deamination important?

Answer 29

Keto acids can be utilised for energy

Question 30

Why is ammonia removed? How?

Answer 30

Very toxic Converted to urea or excreted directly in urine

Question 31

Describe ureas: N content Toxicity Solubility Reactivity

Answer 31

High Non-toxic Water soluble Inert

Question 32

What happens to urea?

Answer 32

Excreted in urine Osmotic role in kidney tubules

Question 33

Where does the urea cycle occur? Using how many enzymes?

Answer 33

Liver Five

Question 34

What increases and decreases levels of the urea cycle?

Answer 34

High protein diet - induces enzymes Low protein diet or starvation - represses enzymes

Question 35

What causes a defect in the urea cycle?

Answer 35

Autosomal recessive genetic disorder Deficient in one of the enzymes

Question 36

What can defects in the urea cycle cause?

Answer 36

Hyperammonaemia Accumulation of urea cycle intermediates

Question 37

Symptoms of defects in the urea cycle

Answer 37

Vomiting Lethargy Irritability Mental retardation Seizures Coma

Question 38

How do you manage defects in the urea cycle?

Answer 38

Low protein diet Replace amino acids in diet with keto acids

Question 39

What are some protential toxic effects of ammonia?

Answer 39

PH effects Interferes with amino acid transport and protein synthesis Alteration of blood brain barrier

Question 40

What are two molecules that allow ammonia to be transported safely?

Answer 40

Glutamate Alanine

Question 41

Describe how glutamate assists the transport of ammonia

Answer 41

Ammonia combined with glutamate - forms glutamine Glutamine transported in blood to liver or kidneys Glutamine cleaved by glutaminase - reforms ammonia and glutamate Liver - ammonia into urea cycle Kidneys - excreted in urine

Question 42

Describe how alanine is involved in ammonia transport

Answer 42

Ammonia combined with pyruvate - forms alanine Alanine transported in the blood to the liver Alanine converted back by transamination Amino group into urea cycle