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Nutrition & Metabolism > W6 - Protein Metabolism > Flashcards

W6 - Protein Metabolism Flashcards

1
Q

What are proteins metabolised to in the stomach?

A

Polypeptides

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2
Q

Where do the polypeptides from the stomach travel to?

A

Small intestine

–where peptidases (secreted from the pancreas + intestinal wall) break them down to:

  • aa, di peptidases + tri peptidases.
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3
Q

What happens to the aa in the small intestine?

A

Absorbed into blood

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4
Q

aa after eating - fed state

A

⬆️ insulin in blood

aa arrive at liver from the hepatic portal vein

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5
Q

aa after eating - fed state

What do the aa do once arrived at the liver

A

Used for protein synthesis

Transported to other tissues

Storage - TAG / Glycogen

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6
Q

aa when not having eaten for a while - fasted state

A

Body needs to make energy

aa broken down as body is in a catabolic state

Glucagon in blood

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7
Q

What are the 2 ways aa can be classified?

A

Glucogenic

Ketogenic

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8
Q

Fate of ketogenic aa

A

Will be converted to AcetylCoA or Acetoacetyl CoA

Then enter TCA cycle if in catabolic situation

OR

Converted back to be stored as fat.

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9
Q

Fate of glucogenic aa

A

Feed into TCA cycle:

  • Used for energy if in catabolic state.

OR

  • If taken in excess aa, store them as CHO
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10
Q

Difference between aa + a-keto acid

A

a-keto acid is an aa but with the N group removed

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11
Q

What happens to the aa that aren’t used for protein synthesis or synthesis of any N containing compounds?

A

Metabolised by transamination or deamination

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12
Q

What is the most common way to remove N from an aa?

A

By transaminating it

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13
Q

How does transamination work/.

A

N group on aa is transferred to an a-keto acid

= Interchangeable reaction

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14
Q

How is deamination carried out?

A

W/ dehydrogenase

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15
Q

What does deamination result in?

A

a-keto acid

NH3

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16
Q

What is transamination important for?

A

Production of non-essential aa

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17
Q

Transaminases are freely reversible but what do they depend on?

A

Substrate availability

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18
Q

Where does transamination occur?

A

Most tissues including the muscle

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19
Q

What do main transamination reactions involve?

A

Alanine

Aspartate

Glutamate

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20
Q

What does the liver do during exercise in regards to alanine?

A

Increases its uptake by about 50%

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21
Q

Why does the liver increase the uptake of alanine during exercise?

A

As it can be converted to pyruvate.

  • Pyruvate can go through gluconeogenesis OR can be oxidised to give energy
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22
Q

Why is aspartate important for nitrogen excretion?

A

Plays a part in the urea cycle

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23
Q

When can transamination be heavily utilised?

A

During periods of starvation or prolonged exercise

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24
Q

Where does oxidative deamination occur?

A

Mit matrix of liver

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25
Q

What happens when there’s a shortage of substrates during oxidative deamination in the liver?

A

Glutamate is broken down to give:

  • NADH (can enter ETC)
  • a-ketoglutarate (can enter TCA cycle)
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26
Q

Which aa is the only aa to contain 2 nitrogens?

A

Glutamine

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27
Q

What can be used to make glutamine?

How?

A

Glutamate

Glutamate + NH4 + ATP –> Glutamine + ADP

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28
Q

Which aa is the most abundant free aa in the skeletal muscle + blood?

A

Glutamine

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29
Q

What is glutamine really important for?

A

Ammonia transport

Gluconeogenic precursor

Helps transfer C + N between skeletal muscle + kidneys

Fuel for GI tract + immune system

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30
Q

What is meant by glutamine being a gluconeogenic precursor?

A

If amino group is lost from glutamine = glutamate

If another is lost = a-ketoglutarate (can enter TCA cycle)

Then can go round + back up through gluconeogensis OR can be used for oxidation.

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31
Q

Example of a cataplerotic loss

A

Losing glutamine from muscles

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32
Q

Where does the urea cycle happen?

A

Liver

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33
Q

UREA CYCLE - STEP 1 (Before actually entering cycle)

NH3 + CO2 + 2ATP—>

By what enzyme?

A

Carbamoyl P + 2ADP

By Carbamoyl P synthetase

IRREVERSIBLE

34
Q

What is carbamoyl P synthetase stimulated by?

A

N-acetylglutamate

35
Q

How does carbamoyl P enter the urea cycle?

A

By combining w/ L-ornithine –> citrulline

36
Q

UREA CYCLE

Citrulline –> L-argininosuccinate

A

Citrulline + ATP + N from aspartate–> L-argininosuccinate + AMP

37
Q

UREA CYCLE

What happens to the fumarate produced between L-argininosuccinate –> L-arginine

A

Leaves + enters TCA cycle

38
Q

In which part of the urea cycle is urea released into the blood?

A

Between L-arginine + L-ornithine

39
Q

What must happen to get the a-keto acid from BCAAs

A

Must be transaminated w/ a-ketoglutarate to get glutamate + the a-ketoacids of BCAAs

Enzyme = BCAT

40
Q

What happens to the glutamate produced from BCAA oxidation?

A

Transaminates to form alanine

Alanine leaves muscle + taken up by liver

41
Q

What then happens to the a-ketoacids of BCAAs?

A

Undergo dehydrogenation by BCKDH

Where H group is removed so they have their own specific dehydrogenase.

42
Q

What does valine make after the BCAA oxidation?

A

Succinyl CoA

  • Glucogenic aa
43
Q

What does isoleucine make after the BCAA oxidation?

A

Succinyl CoA
- Glucogenic aa

Also creates acetyl-CoA
- Ketogenic

44
Q

What does leucine make after the BCAA oxidation?

A

Acetyl CoA + Acetoacetyl CoA

  • Ketogenic
45
Q

Where does glycogenolysis occur?

A

Muscle

46
Q

What does glycogenolysis result in?

A

G-6-P which can go further through glycolysis to create pyruvate.

47
Q

Glucose-Alanine cycle

Pyruvate created from G-6-P in glycogenolysis. What can happen to it?

A

Can transaminate w/ an aa to form Alanine in the muscle.

Released into blood.

Taken up by liver

Undergoes transamination w/ a-ketoglutarate –> glutamate + pyruvate.

48
Q

What can happen with the pyruvate formed from the glucose-alanine cycle when in the liver?

A

Can go through gluconeogenesis.

Glucose can be released back into blood + transported to wherever needed.

49
Q

Glucose alanine cycle

What happens to the glutamate in the liver?

A

Deaminated

NH3 lost through urea OR used to make plasma proteins.

50
Q

How is net protein balance calculated?

A

Protein synthesis - Protein breakdown

51
Q

Transcription

How is it controlled?

A

By:

Transcription factors

Coactivator proteins

Repressors

52
Q

Transcription

How is it controlled?

What comes under transcription factors?

A

Activators

Enhancer sites

53
Q

Transcription

How is it controlled?

What comes under coactivator proteins?

A

Signals

54
Q

Transcription

How is it controlled?

What comes under repressors?

A

Silencer

55
Q

Role of tRNA

A

Brings aa to mRNA

56
Q

What catalyses the binding of aa to the appropriate tRNA

A

Aminoacyl tRNA synthetase

57
Q

3 stages of translation

A

Initiation

Elongation

Termination

58
Q

What does the process of initiation of translation involve?

A

40s + 60s ribosomal units

mRNA mol

Initial aminoacyl-tRNA (tRNA mol w/ methionine attached)

Protein factors to control initiation process

Energy from GTP

59
Q

Examples of the protein factors to control the initiation process of translation

A

p70s6 kinase

60
Q

What does elongation in translation involve?

A

Addition of aa to carboxyl terminal end of polypeptide chain

61
Q

Why does elongation in translation occur?

A

Anticodon of aminoacyl-tRNA recognises 2nd codon on mRNA

62
Q

Elongation in translation

Where does the peptide bond occur?

A

Between carboxyl group of MET + 2nd aa (still attached to tRNA)

63
Q

Termination in translation

What does the termination / release factor do?

A

Releases the complete polypeptide chain from the last tRNA

80s dissociates to its 2 x 40s + 60s subunits.

64
Q

Post-translational control of protein function

What is it regulated by?

A
  • Chaperones

- Scaffolding proteins

65
Q

What are the 5 main pathways in which protein can be broken down?

A

Ubiquitin-proteosome

Lysosomal proteolysis

Caspases

Matrix metalloproteases

Calpain

66
Q

How can muscle protein synthesis + breakdown be measured?

A

By looking at:

Fractional synthetic rate (FSR)

OR

Fractional breakdown rate (FBR)

67
Q

How is fractional synthetic rate typically measured?

A

Biopsies and Isotopes

68
Q

At rest what is greater? - Muscle protein synthesis or muscle protein breakdown

A

Muscle protein breakdown

69
Q

When taking a muscle biopsy, what muscle protein fractions do you separate out?

A

Collagen

Myofibrillar proteins

Mitochondria proteins

Sarcoplasmic proteins

70
Q

Which of the muscle proteins is more associated with resistance type exercise?

A

Myofibrillar proteins

71
Q

Which of the muscle proteins is more associated with endurance type exercise?

A

Mitochondrial proteins

72
Q

What does exercise do to net muscle protein balance?

A

Improves it but still no positive values are reached.

73
Q

Availability of substrates in the human body.

Where can the CHO be?

A

Plasma glucose

Liver glycogen

Muscle glycogen

74
Q

Availability of substrates in the human body.

Where can the fats be?

A

Plasma FAs

Plasma TAGs

Muscle TAGs

Adipose tissue

75
Q

How does the VO2 max test step protocol work in the fat max test?

A

Start at low intensity at 60W on a bike.

⬆️W by 35 every 3 mins.

76
Q

When collecting data for the VO2 max test step protocol in the fat max test, which data do you collect and disregard?

A

Disregard = 1st min of each workload

Calculate = Average of final 2 mins

77
Q

Where can BCAA be oxidised?

A

Kidneys + muscle

78
Q

What happens to net balance following resistance exercise ONLY

A

⬆️ but remains -ive

79
Q

When BCAAs are oxidised, what is their N group generally used to form?

A

Glutamate + then alanine

80
Q

Where does the decarboxylation of a-ketoacids involving branched chain a-keto acid dehydrogenase occur?

A

In the mit

81
Q

Which protein breakdown system is most likely to be used in the muscle following exercise?

A

Calpain system

82
Q

Which amino acid is always the first in a polypeptide chain?

A

Methionine

Nutrition & Metabolism (17 decks)

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