Protein Metabolism Flashcards Preview

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Flashcards in Protein Metabolism Deck (18)
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1
Q

Protein metabolism in the liver

A
  • breakdown of amino acids
  • formation of urea for removal of ammonia from body fluids
  • formation of virtually all plasma proteins
  • manipulation of amino acids and synthesis of other “stuff” from amino acids
2
Q

What is protein used for?

A
  • energy
  • gluconeogenesis/ketogenesis
  • enzymes
  • transport proteins
  • structural support
  • muscles
3
Q

Amino acids

A

Building blocks of proteins

  • all have an acidic group (-COOH) and a nitrogen atom attached (NH2)
  • approx 20 AA in the body
  • arranged into chains via peptide linkages to form proteins
  • average protein size is 400 AA
4
Q

Are amino acids weak or strong?

A

All are weak acids

  • protein digestion in GIT takes 2-3 hrs = final breakdown is AA
  • once in blood, cells absorb AA within 5-10 min to prevent build up of circulating AA
5
Q

Amino acid entry into cells

A

AA are too large for diffusion

  • requires facilitated diffusion or active transport
  • AA that make it to the kidneys are mostly resorbed by proximal convoluted tubule
6
Q

Amino acid fate inside cells

A

Turnover is rapid

  • AA are quickly used up to make proteins inside the cell
  • most intracellular proteins can be degraded rapidly to yield AA
  • constant cycle of AA –> protein –> AA –> protein
  • not much is stored, any excess proteins are used for energy or converted to fat or glycogen
7
Q

What does the body prefer for its main energy sources?

A

CHO and fats

  • spares proteins for other body functions
  • after starvation, AA are used primarily for energy
8
Q

Growth hormone and insulin ______ formation of tissue protein

A

Increase

9
Q

Glucocorticoids

A

Increase plasma concentrations of AA

  • break down extrahepatic proteins to provide AA for energy
  • increase protein production in the liver
  • oral steroids can cause muscle wasting
10
Q

Testosterone

A

Increases protein deposition in tissues, especially muscles

11
Q

Thyroxine

A

Increase rate of protein synthesis, or increase the rate of protein degradation for energy

12
Q

Protein functions

A
  • plasma proteins
  • essential and non-essential amino acids
  • source of energy
13
Q

Plasma protiens

A

Albumin: provides oncotic pressure, transporter, involved in healing
Globulins: immunity and enzyme functions
- 50-80% made in the liver
Fibrinogen: polymerizes into fibrin to form blood clots
- mostly made in liver

14
Q

Essential AA

A

Cannot be synthesized and therefore must be in diet

  • arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
  • cats also require taurine
15
Q

Non-essential AA

A

Synthesized by body from keto-acids, which are precursors to the AA

  • process known as transamination
  • aminotransferase enzymes are derived from vitamin B6, pyridoxine
16
Q

Degradation

A

Occurs in liver via deamination (removal of amino group via aminotransferase)

  • amino group is transferred to another molecule or released in form of ammonia (NH3)
  • yields NADH + H + NH3
  • yields a keto-acid –> TCA cycle
17
Q

Protein breakdown products are used for

A

Gluconeogenesis or ketogenesis

18
Q

Urea cycle

A

Occurs in the liver

  • controls ammonia levels in the body
  • ammonia (NH3) from deamination –> urea –> renal excretion
  • prevent hepatic encephalopathy