Protein

Question 1

terms

Answer 1

Muscle protein synthesis

Muscle protein breakdown

Net balance

Turnover

Question 2

interaction between PS, PB and net protein balance

Answer 2

Protein Synthesis - Protein Breakdown = net protein balance

PB exceeds PS = negative protein balance → protein loss

PS exceeds PB = positive protein balance → protein gain

Question 3

net protein balance and energy

Answer 3

Protein synthesis and protein breakdown are often linked

As much as 20% of basal energy exp
Formation of RNA
Make peptide chain

~300g/d turnover

Protein half-lives vary
Some enzymes <1h
Important to respond to changing conditions
Other proteins (e.g. myofibrillar) days/weeks

Question 4

why spend such energy to continually turnover proteins

Answer 4

Gene expression

Selective gene expression determines the structural and functional characteristics of the various
cell types

Genes may be expressed, but proteins must be activated, modified and/or converted

Question 5

protein synthesis processes

Answer 5

Transcription

Translation

Post-translational modification and targeting to ensure proteins are activated

Complex regulation at any of these steps

Question 6

transcriptional control

Answer 6

Transcription factors

Activators
Enhancer sites

Coactivator proteins
Signals

Repressors
Silencer

Regulation of RNA Polymerase

Question 7

tRNA charging

Answer 7

AA + ATP + tRNA → aminoacyl-tRNA +AMP + Pi

Aminoacyl tRNA synthetase – catalyses binding of AA to appropriate tRNA

Amino acids activated by ATP

AA transfer to specific tRNA
Each tRNA has a specific anticodon
Specificity is crucial
tRNA synthetase contains proofreading site

tRNA charging is an irreversible process

Question 8

processes of translation

Answer 8

Initiation

Elongation

Termination

Question 9

initiation

Answer 9

The process of initiation of translation involves:

40S and 60S ribosomal subunits

mRNA molecule

the initial aminoacyl-tRNA (methionyl-tRNA) (tRNA molecule with methionine attached)

a number of protein factors to control the initiation process, e.g. p70s6 kinase, eIF4E, etc.

Energy from GTP

Question 10

elongation

Answer 10

Involves the addition of amino acids to the carboxyl terminal end of the polypeptide chain

The process occurs because the anticodon of aminoacyl-tRNA recognises the second codon on the mRNA

A peptide bond occurs between the carboxyl group of MET and the second amino acid (which is still attached to its tRNA

Question 11

termination

Answer 11

The process continues (three bases at a time) until a stop codon is reached.

The stop codon is recognised due to the specificity of the mRNA

A termination factor releases the complete polypeptide chain from the last tRNA and the 80S disassociates to its two 40S and 60S subunits

Question 12

post-translational processing

Answer 12

After the polypeptide is released from the translational apparatus, it requires further processing before it is in
physiologically active form and
the cell location where it becomes functional.

A growing protein will begin to fold as it is being made and proteins have the capacity to self fold - However, many complex proteins need help to fold.

Molecular chaperones or chaperonins, e.g heat shock proteins (Hsp).

Scaffolding proteins

Question 13

control sites

Answer 13

reg of RNA P’s

reg of translation

reg of post-translational control

Question 14

reg of RNA P

Answer 14

Repressors

Activators

Chromatin

Histone acetylation

Question 15

reg of translation

Answer 15

Initiation factors

Elongation factors

Question 16

reg of post-translational control

Answer 16

Chaperones

Scaffolding proteins

Question 17

3 reasons why protein limited fuel in ex

Answer 17

1. primary role provides AA building blocks for tissue synthesis
2. early studies show only minimal PB during endurance ex as reflected by urinary N excretion
3. theoretical computations and exp evidence of protein requirements for muscle tissue synthesis with resistance training

Question 18

what does protein as a fuel rely on?

Answer 18

energy expenditure and nutritional status

applies to branched chain AAs leucine, valine and isoleucine oxidised in skeletal muscle rather than in liver

Question 19

after endurance and resistance type ex what happens to muscle PS?

Answer 19

increases

Question 20

what 2 factors justify re-examining protein intake recommendations involved in ex?

Answer 20

increased PB during prolonged ex and intense training

increased PS in recovery

Question 21

In normal healthy individuals body proteins can be excreted as?

Answer 21

hair

skin

Question 22

Which protein breakdown system is predominantly involved in apoptosis?

Answer 22

caspases

Question 23

muscle protein synthesis

Answer 23

Building up of amino acids into functioning muscle

Question 24

muscle protein breakdown

Answer 24

Degradation of polypeptide chains within a muscle

Question 25

net balance

Answer 25

Relationship between synthesis and breakdown

Question 26

turnover

Answer 26

Constant use and restoration of protein

Question 27

regulation of RNA polymerase in transcriptional control

Answer 27

General factors
Specific factors

Hormones
Specific (steroids)
Secondary messenger (cAMP)