Energy Storage - Protein Flashcards Preview

Lizzie's Metabolism > Energy Storage - Protein > Flashcards

Flashcards in Energy Storage - Protein Deck (31):
0

Where does stage 1 of the catabolism of protein occur?

In the GI tract

1

What happens during stage 1 of the catabolism of proteins?

Proteases and peptidases hydrolyse peptide bonds to release free amino acids. They are then absorbed into the circulation.

2

What can the amino acids be used for?

Protein synthesis
Synthesis of N containing compounds

3

What does it mean if an amino acid is ketogenic?

Once the amine group is removed, it's C skeleton can be converted to acetyl CoA which can go onto make ketone bodies

4

What does stage 2 catabolism of amino acids produce?

Acetyl CoA
Oxaloacetate
Alpha-ketoglutarate
Fumarate
Succinate

5

How much nitrogen is in the body of a 70kg man?

2kg

6

What does nitrogen leave the body as?

Urea, ammonia, creatinine, uric acid, urine.
Also lost in skin and hair.

7

When would someone have a positive N balance?

Growth, tissue repair, pregnancy, convalescence

8

When is there a negative N balance?

Starvation, trauma, malnutrition

9

List the 8 essential amino acids

Lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, methionine

10

What happens to the excess amino acids?

Converted to intermediates of carbohydrate and lipid metabolism or oxidised to produce energy

11

What is the major site of the breakdown of amino acids?

The liver

12

What are the three common features of amino acid catabolism?

C atoms converted to intermediates of carbohydrate and lipid metabolism
Usually start with the removal of the amine group (transamination/deamination)
N atoms converted to urea

13

What stimulates transaminases?

Cortisol

14

Which two transaminases are clinically important and why?

Alanine aminotransferase (ALT/GPT)
Aspartate aminotransferase (AST/GOT)

Measured in serum to assess liver function

15

Which enzyme is normally deficient in phenylketonuria and and what does it normally do?

Phenylalanine hydroxylase

Oxidises phenylalanine to tyrosine

16

In PKU, what happens to phenylalanine when it accumulates in tissues? What effect does this have?

Metabolised to phenylpyruvate
It inhibits pyruvate uptake by mitochondria and interferes with energy metabolism in the brain.
-> inhibition of brain development

17

How is PKU diagnosed?

Detection of phenylketones in urine or measurement of blood phenylalanine concentration (normally less than 0.1mmol/L but can exceed 1mmol/L in PKU)

18

What type of inheritance is homocystinuria?

Autosomal recessive

19

What is the deficient enzyme in homocystinuria and what does it normally do?

CBS
Normally converts homocysteine to cystathionine. This is further converted to cysteine.

20

What happens in homocystinuria?

Deficient CBS enzyme so homocysteine levels increase in the blood. Some is converted to methionine so this is increased. Homocystine (oxidised form) can be found in the urine.

21

What does homocystinuria cause?

Disorders of connective tissue, muscle, CNS and cardiovascular system. Can therefore be confused with Marfan's syndrome in children.

22

What is hyperammonaemia associated with?

Blurred vision, tremors, slurred speech, coma, death

23

How does ammonia get into the body?

Produced by many tissues and can be absorbed from the gut

24

What enzyme converts ammonia to glutamine and what else is needed?

Glutamine synthetase
Glutamate and ATP

25

What does glutaminase do?

Hydrolyses glutamine to ammonia and glutamate in the kidneys

26

How is the urea cycle regulated?

Enzymes are inducible.
High protein diet induces enzymes.
Low protein diet represses enzymes.

27

What does a deficient enzyme in the urea cycle cause?

Complete loss
-fatal

Partial loss
-hyperammonaemia
-accumulation/excretion of a urea cycle intermediate

28

Symptoms of a deficiency in an enzyme of the urea cycle?

Irritability, vomiting, lethargy
Seizures, coma, death

29

How is a deficiency in one of the enzymes of the urea cycle treated?

Low protein diet

30

How is ammonia thought to be toxic?

Removes alpha-ketoglutarate from the TCA cycle.
Reacts with it to form glutamate via the enzyme glutamate dehydrogenase