Skeletal Muscle Regulation – Biochemical and Physiological Control of Muscle Turnover

Question 1

What is muscle protein turnover

Answer 1

It is defined by the balance between protein synthesis (anabolic) and protein degradation (catabolic)

Question 2

Difference between essential and on-essential amino acids

Answer 2

Nine of these are considered to be essential AAs
Body is unable to synthesise them
Must be obtained from diet in appropriate amounts for normal muscle growth and development

Other 11 AAs are non-essential
These can be produced from other AAs in the diet

Question 3

2 types of hypertrophy

Answer 3

Myofibrillar hypertrophy – increase in number/size of contractile proteins
Sarcoplasmic hypertrophy – disproportionate increase in volume of sarcoplasm relative to MFH

Question 4

Function of satellite cells in muscles

Answer 4

Satellite cells function to facilitate growth, maintenance, and repair of damaged SM
Usually dormant, but become activated when muscle fibre receives any form of trauma, damage, or injury

Question 5

How to satellite cells work

Answer 5

Satellite cells proliferate and the daughter cells move to the area of damage

They then fuse with the existing muscle fibre and donate their nuclei which helps to regenerate the damaged fibre

This increases the number of contractile proteins (actin and myosin)

Question 6

How do cytokines assist in hypertrophy

Answer 6

Loading causes trauma to skeletal muscle
Immune system responds to repair the damage and removes waste products from injured area
Cytokines stimulate lymphocytes and monocytes (amongst others) to site of damage to repair tissue
This leads to an increase in muscle size = hypertrophy

Question 7

Purpose of testosterone in muscle growth

Answer 7

Promotes an increase in the rate of protein synthesis and inhibits protein breakdown
Promotes satellite cells replication and activation

Question 8

Function of growth hormone for hypertrophy

Answer 8

Promotes satellite cell activation and proliferation via stimulation of insulin-like growth factor (IGF)

Question 9

What is ubiquitin a marker of and how is does it attach t proteins

Answer 9

Ubiquitin is marker of cellular proteins which are being degraded

Ubiquitin is activated and attchedd to proteins via the enzymes E1, E2, E3

Question 10

What happens to proteins that are poyubiquinated

Answer 10

degraded by proteosomes

Question 11

What two factors does protein synthesis rate depend on

Answer 11

Translational efficiency – protein synthesis per unit amount of RNA
Translational capacity – total ribosome content per unit tissue

Question 12

What is the purpose of mammalian target of rapamycin (mTOR)

Answer 12

major signalling pathway for initiating protien synthesis

Results in increased translational efficiency

Question 13

What molecules are able to induce skeltal muscle hypertrophy via mTOR

Answer 13

IGF-1

insulin

Question 14

mTOR pathway

Answer 14

IGF-1/insulin stimulates PI3 kinase, activating Akt
Akt promotes phosphorylation of mTOR
This then causes:
-Phosphorylation of 4EBP-1
-prevents 4EBP-1 from binding to elF4E
-unbound elF4E now join with other TF 
-Activation of p70S6K

Results in skeletal muscle hypertrophy

Question 15

What inhibits FoxO pathway

Answer 15

Akt phosphorylation

Question 16

What activates NF-kB pathway

Answer 16

Cytokines like TNF-alpha and IL-6

Question 17

What activates NF-kB pathway

Answer 17

Cytokines like TNF-alpha and IL-6