Lecture 11 - Amino Acid Metabolism

Question 1

functions of the muscle in protein metabolism:

Answer 1

(1) serves as a reservoir of amino acids

(2) the major site of break-down of muscle protein

(3) utilises branched chain amino acids (BCAA) as a fuel source

(4) muscle can provide crucial precursors for gluconeogenesis during times of fasting. this is via glucose alanine cycle

Question 2

vigorously working muscles operate nearly _____________ and rely on __________ for energy:

Answer 2

(1) anaerobically

(2) glycolysis

Question 3

glycolysis yields:

Answer 3

pyruvate

Question 4

what can pyruvate be converted into:

Answer 4

pyruvate can be converted into alanine for transport in the liver via the cardiovascular system

Question 5

transamination:

Answer 5

the process of the transfer of an amino group to a ketoacid to produce a new amino acid

Question 6

to make the carbon skeleton available as a metabolic intermediate the:

Answer 6

amino group must be removed

Question 7

how is the toxic amino group / ammonia dealt with in the body?

Answer 7

achieve through transfer to another ketoacid intermediate

Question 8

ketoacid + amino group =

Answer 8

new amino acid

Question 9

how is pyruvate resulting from glycolysis in the muscle converted to alanine?

Answer 9

via transamination - the pyruvate accepts the amino group from glutamate in the muscle and is converted to alanine

Question 10

where does alanine travel to once it is produced?

Answer 10

the liver

Question 11

what happens to alanine once it reaches the liver?

Answer 11

upon reaching the liver the alanine is converted back to pyruvate via transamination through donating an amino group to alpha-ketoglutarate which forms glutamate

Question 12

the non-essential amino acid glutamate is synthesised using a:

Answer 12

transaminase reaction

Question 13

what does alanine aminotransferase do?

Answer 13

it transfers the amino group (NH3+) from alanine to alpha-ketoglutarate, a reaction that produces intermediates pyruvate and glutamate

Question 14

when is amino acid metabolism most active?

Answer 14

Amino acid metabolism is most active after a high protein meal

•Particularly if that meal is low in carbohydrate

•Can be oxidised or used to make glucose (gluconeogenesis in the liver or kidney)

Question 15

what occurs during short term starvation where there is an absence of fatty acids to feed into the TCA or glucose:

Answer 15

•Tissue protein is broken down into amino acids constituents
•Amino acids are catabolised into their carbon skeletons which feed into intermediary metabolism to give you energy
•Allows the liver to maintain blood glucose

Question 16

what molecules are crucial in transporting amino groups around the body?

Answer 16

glutamate and alanine

Question 17

what is the major amino acid found in muscle?

Answer 17

the major amino acid in muscle protein is the branched chain amino acid (BCAA) LEUCINE

Question 18

what happens to muscle during periods of fasting?

Answer 18

during periods of fasting, skeletal muscle protein is degraded into its amino acid constituents

Question 19

what is always taking place in the muscle?

Answer 19

there is always glycolysis occurring n the muscle

Question 20

If there are supply of BCAA in our diet and if they are present in the plasma…

Answer 20

muscles use them as fuel resulting in ammonia ions which are stored in forms of glutamate, glutamine and alanine

Question 21

what is the glucose-alanine cycle primarily a mechanism for?

Answer 21

it is primarily a mechanism for skeletal muscle to eliminate nitrogen while replenishing its energy supply

Question 22

what is alanine fuel for?

Answer 22

alanine is fuel for gluconeogenesis (via pyruvate) in the liver to produce glucose which is transported back to the muscle

Question 23

where can glutamine come from?

Answer 23

glutamine can come from anywhere in the body

Question 24

how do most other tissues (non-muscle-tissue) break down protein as a fuel source without using glucose?

Answer 24

most other tissues use amino acid deaminases to catabolise amino acids to provide the carbon skeletons as a fuel source

Question 25

the many uses for amino acids within the body:

Answer 25

•Arginine: spermine, spermidine, putrescine. Polyamines synthesised when cells are stimulated to divide •Aspartate: pyrimidines (cytosine, thymine, uracil) •Glycine: purines (adenine, guanine), glutathione (protects against oxidative stress), creatine (creatine phosphate is a high energy intermediate) •Histidine: histamine (inflammatory response) •Serine: phosphatidylserine, sphingosine (lipid components of membranes) •Phenylalanine: adrenaline and noradrenaline (hormones) •Tryptophan: nicotinic acid (NAD) and serotonin (neurotransmitter) •Valine: Pantothenic acid (coA)

Question 26

amino acids as building blocks for hormones:

Answer 26

•Decarboxylation is a crucial event in the processing of amino acids into hormones •All the decarboxylases have the cofactor Pyridoxal 5’ phosphate (PLP) at their activate site and results I the removal of CO2 •These processes are crucial for the production of neurotransmitters

Question 27

Glutamate is decarboxylated into the GABA neurotransmitter:

Answer 27

•Glutamine taken up into the neurons from surrounding cells such as glial cells •Processed into Glutamate by glutaminase •Glutamate decarboxylated into GABA by glutamate decarboxylase •GABA packaged into vesicles and then released into the synaptic cleft •Can be taken up by post synaptic neurons

Question 28

tyrosine is important for maintaining neuronal signalling:

Answer 28

•Tyrosine taken into the neuron and converted into DOPA •Aromatic amino acid decarboxylase (AAAD/AADC) produces Dopamine which can either signal or be turned over my monoamine oxidase (MAO) •Dopamine levels are important to control movement and mood – release of Dopamine is our brains reward system •Many therapeutics function to either stabilise Dopamine or manipulate its levels in the synaptic cleft