Muscle Proteins, Degration And N Metabolism

Question 1

How much muscle is continuously being degraded and resynthesised per day?

Answer 1

500g

Question 2

2 major mechanisms in muscle catabolism

Answer 2

Ubiquitin proteosome protein degradation system;
Autophagy - via the lysosome;
Minor: calcium-activated proteases

Question 3

Muscle breakdown

Answer 3

Needed for muscle repair (for example, exercise);

Leads to muscle atrophy (breakdown exceeds synthesis)

Question 4

Cachexia

Answer 4

Breakdown exceeds synthesis;
Late stages of HIV and cancer;
Involves cytokines being released (TNFa);
Increase in enzymes in the ubiquitin-proteosome pathway

Question 5

Amino acid converted to proteins (muscle) and vice versa by?

Answer 5

Ubiquitin-protease pathway;
Calpain;
Lysosomal

Question 6

Amino acids conversion to urea involves?

Answer 6

Removal of N group t form ammonium ion;

Ammonium ion to urea by the urea cycle

Question 7

Nitrogen balance

Answer 7

Difference between N intake (protein) and N excreted (urea)

Question 8

Positive nitrogen balance due to?

Answer 8

Pregnancy;
Growing child;
Tissue repair after injury;

Question 9

Negative nitrogen balance due to?

Answer 9

Inadequate protein intake or increased protein degradation;
Illness;
Fever;
Cancer cachexia;
Starvation;
Ageing;

Question 10

Kwashiorkor is due to?

Answer 10

Negative nitrogen balance

Question 11

Site of amino acid catabolism to urea

Answer 11

Liver

Question 12

How is nitrogen transported from the muscle to the liver?

Answer 12

Alanine and glutamate

Question 13

How is the ammonium ion formed?

Answer 13

Transamination;

Oxidative deamination;

Question 14

Transamination with aspartate

Answer 14

Aspartate + alpha-ketoglutarate is converted to oxaloacetate and glutamate (catalysed by aspartate amino transferrase)

Question 15

Transamination with alanine

Answer 15

Alanine + alpha-ketoglutarate converted to pyruvate + glutamate
Catalysed by alanine aminotransferrase

Question 16

Oxidative demamination

Answer 16

Glutamate + NAD+ converted to alpha-ketoglutarate + ammonium ion + NADH
Catalysed by glutamate dehydrogenase

Question 17

Urea cycle takes place in?

Answer 17

Cytosol and mitochondrial matrix;

Question 18

Glucogenic amino acids

Answer 18

Carbon skeletons used for glucose synthesis

Question 19

Ketogenic amino acids

Answer 19

Carbon skeletons increase ketone bodies; yield Acetyl CoA and Acetoacetate;

Question 20

Inherited diseases of amino acid metabolism

Answer 20

Many aminoacidopathies;

Phenylketonuria