1.11 - Amino Acid Metabolism

Question 1

functions of muscle in protein metabolism (4)

Answer 1

1. reservoir of amino acids
2. major site of muscle protein break-down
3. utilises branched chain amino acids (BCAAs) as fuel source
4. can provide crucial precursors for gluconeogenesis during times of fasting (glucose-alanine cycle)

Question 2

what happens if pyruvate isnt eliminated?

Answer 2

lactic acid build up

Question 3

how can pyruvate be transported to liver? (2)

Answer 3

1. pyruvate converted to alanine
2. transported to liver via cardiovascular system

Question 4

transamination

Answer 4

transfer of amino group to a ketoacid to produce new amino acid

Question 5

purpose of amino group removal

Answer 5

to make carbon skeleton available as metabolic intermediate

Question 6

how are the toxic amino group/ammonia (NH4) dealt with?

Answer 6

transfer to ketoacid intermediate (transamination)
(such as pyruvate, a-ketoglutarate and oxaloacetate)

Question 7

pyruvate conversion to alanine (transamination)

Answer 7

pyruvate accepts amine group from glutamate

Question 8

What is given as a result of glutamate donating amine to pyruvate

Answer 8

a-ketoglutarate

Question 9

when can a-ketoglutarate be used in muscle?

Answer 9

if theres enough N

Question 10

why is alanine less likely to affect blood pH?

Answer 10

it is a neutral amino acid

Question 11

cori cycle

Answer 11

lactic acid transported back to liver to be converted back to glucose (gluconeogenesis)

Question 12

how is alanine converted back to pyruvate in the liver?

Answer 12

alanine donates amine group to a-ketoglutarate producing pyruvate and glutamate (transamination)

Question 13

what is given as a result of a-ketoglutarate accepting an amine group from alanine (liver)

Answer 13

glutamate (will enter urea cycle)

Question 14

alanine aminotransferase

Answer 14

transfers amino group (NH3+) from alanine to a-ketoglutarate

Question 15

metabolic intermediates produced in the reaction of a-ketoglutarate accepting an amino group from alanine (2)

Answer 15

1. pyruvate
2. glutamate

Question 16

amino acid metabolism during short term starvation in an absence of fatty acids to feed into TCA, or glucose (2)

Answer 16

1. tissue broken down -> amino acid constituents
2. amino acids catabolised -> carbon skeletons (feed into intermediary metabolism to give energy)

Question 17

glutamine and alanine role in allowing liver to maintain blood glucose

Answer 17

crucial in transporting amino groups around the body

Question 18

major amino acid in muscle protein

Answer 18

branched chain amino acid (BCAA) leucine

Question 19

how is a-ketoglutarate converted to glutamate

Answer 19

ammonia ion received

Question 20

alanine, glutamate and glutamine fundamental function

Answer 20

transporting ammonia/nitrogen around body

Question 21

how can glucose be supplied to muscle (constant glycolysis) (2)

Answer 21

1. via CVS from plasma
2. solubilised from glycogen store

Question 22

primary mechanism for skeletal muscle to eliminate nitrogen while replenishing energy via BCAAs (3)

Answer 22

1. if BCAA present in plasma (diet) - muscle cells use them as fuel
2. resulting ammonium ions stored in forms of glutamate, glutamine and alanine
3. ideal forms of amino acids to be transported via CVS

Question 23

what is alanine fuel for?

Answer 23

gluconeogenesis (via pyruvate) in liver

Question 24

glucose-alanine cycle (3)

Answer 24

1. during periods of fasting, skeletal muscle protein degraded -> amino acid constituents
2. ultimately processed -> alanine, transported in blood to liver
3. alanine fuels gluconeogenesis (via pyruvate) in liver -> glucose -> back to muscle

Question 25

what amino acid constituents in muscle protein are used as fuel?

Answer 25

carbon skeleton (and other BCAAs)

Question 26

how do most other tissues get carbon skeletons from amino acids?

Answer 26

use amino acid deaminases to catabolise amino acids -> carbon skeletons

Question 27

why is glutamine good for transporting amino groups around body?

Answer 27

can come from any tissue in body

Question 28

role of glutamine in ammonia ion group excretion

Answer 28

glutamine transported to kidney where it feeds into the urea cycle (glutamine cycle)

Question 29

role of intrinsic structural relationship between amino acids and metabolic intermediates

Answer 29

means cells can do reverse and use metabolites to produce amino acids

Question 30

crucial event in processing amino acids -> hormones

Answer 30

decarboxylation

Question 31

cofactor of all decarboxylases

Answer 31

pyridoxal 5' phosphate (PLP)

Question 32

what does the decarboxylase reaction result in?

Answer 32

Removal of CO2

Question 33

glutamine to GABA neurotransmitter (4)

Answer 33

1. glutamine taken up into neurons 2. processed -> glutamate by glutaminase 3. glutamate decarboxylated -> GABA by glutamate decarboxylase 4. GABA packaged into vesicles and released into synaptic cleft

Question 34

role of tyrosine in maintaining neuronal signalling (2)

Answer 34

1. tyrosine taken into neuron, converted -> DOPA 2. aromatic amino acid decarboxylase (AAAD/AADC) produces dopamine (can either signal or turned over by monoamine oxidase (MAO))