Amino Acid Metabolism

Question 1

List the sources of free amino acids in the body

Answer 1

1) degradation of ingested protein
2) biosynthesis of some, but not all, of the amino acids
3) degradation of endogenous protein

Question 2

What are free amino acids used for

Answer 2

synthesis of endogenous protein

carbon skeletons

energy production (urea biproduct)

Question 3

Essential vs non essential amino acids

Answer 3

non essential can be synthesized from precursor molecules in the body.

essential must be supplied in diet

Question 4

Can synthesis of amino acids be sufficient for synthesis of amino acids when dietary protein is not available.

Answer 4

No because the synthesis of most proteins requires all amino acids

Question 5

essential amino acids

Answer 5

arginine

histidine

isoleucine

leucine

lysine

methionine

phenylalanine

threonine

tryptophan

valine

Question 6

non essential amino acids

Answer 6

alanine

asparagine

aspartate

cysteine

glutamate

glutamine

glycine

proline

serine

tyrosine

Question 7

describe the turnover of endogenous proteins, indicating the range of half lives of endogenous proteins and the amount of protein turned over each day

Answer 7

turnover rates vary based on protein and tissue. Half lives can be from minutes to days. Regulatory proteins are degraded and resynthesized at faster rates.

adults degrade ans resynthesize 2-3% (300g) of their total body protein every day.

**there is no net accumulation of protein, even on a high protein diet, excess amino acids are degraded and not stored **

Question 8

two primary pathways for protein degradation

Answer 8

ATP dependent ubiquitin proteosome system and the lysosomal pathway

Question 9

how many grams of protein does the body degrade every day even if dietary protein is not supplied

Answer 9

55g

if you injest less than this you get loss of body protein

if protein intake is greater than 55g the excess amino acids are degraded and not stored

Question 10

What is the fate of the degraded carbon skeletons

Answer 10

nitrogen of the amino group is incorportated into urea and excreted

The carbons skeletons are converted to compunds that can be either used immediately for energy or stored as glycogen or fat for future energy production

Question 11

Define nitrogen balance

Answer 11

nitrogen ingested (primarily as protein) - nitrogen excreted (primarily as urea)

Question 12

predict nitrogen balance status for various physiological situations

Answer 12

normal adult = 0. rate of protein synthesis = rate of degradation

children, pregnancy, body building = positive nitrogen balance. nitrogen injested is greater than excreted. protein synthesis occurs at a higher rate than protein degradation and N accumulates

Starvation, protein malnutrition, trauma, infection, cancer, burn injury, sepsis, surgery = negative nitrogrn balance. the amount of nitrogen excreted it more than injested/synthesized