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Flashcards in Protein Metabolism Deck (18)
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1

Protein metabolism in the liver

- 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

What is protein used for?

- energy
- gluconeogenesis/ketogenesis
- enzymes
- transport proteins
- structural support
- muscles

3

Amino acids

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

Are amino acids weak or strong?

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

Amino acid entry into cells

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

Amino acid fate inside cells

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

What does the body prefer for its main energy sources?

CHO and fats
- spares proteins for other body functions
- after starvation, AA are used primarily for energy

8

Growth hormone and insulin ______ formation of tissue protein

Increase

9

Glucocorticoids

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

Testosterone

Increases protein deposition in tissues, especially muscles

11

Thyroxine

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

12

Protein functions

- plasma proteins
- essential and non-essential amino acids
- source of energy

13

Plasma protiens

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

Essential AA

Cannot be synthesized and therefore must be in diet
- arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
- cats also require taurine

15

Non-essential AA

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

Degradation

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

Protein breakdown products are used for

Gluconeogenesis or ketogenesis

18

Urea cycle

Occurs in the liver
- controls ammonia levels in the body
- ammonia (NH3) from deamination --> urea --> renal excretion
- prevent hepatic encephalopathy