Lecture 11 - Amino Acid Metabolism Flashcards
functions of the muscle in protein metabolism:
(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
vigorously working muscles operate nearly _____________ and rely on __________ for energy:
(1) anaerobically
(2) glycolysis
glycolysis yields:
pyruvate
what can pyruvate be converted into:
pyruvate can be converted into alanine for transport in the liver via the cardiovascular system
transamination:
the process of the transfer of an amino group to a ketoacid to produce a new amino acid
to make the carbon skeleton available as a metabolic intermediate the:
amino group must be removed
how is the toxic amino group / ammonia dealt with in the body?
achieve through transfer to another ketoacid intermediate
ketoacid + amino group =
new amino acid
how is pyruvate resulting from glycolysis in the muscle converted to alanine?
via transamination - the pyruvate accepts the amino group from glutamate in the muscle and is converted to alanine
where does alanine travel to once it is produced?
the liver
what happens to alanine once it reaches the liver?
upon reaching the liver the alanine is converted back to pyruvate via transamination through donating an amino group to alpha-ketoglutarate which forms glutamate
the non-essential amino acid glutamate is synthesised using a:
transaminase reaction
what does alanine aminotransferase do?
it transfers the amino group (NH3+) from alanine to alpha-ketoglutarate, a reaction that produces intermediates pyruvate and glutamate
when is amino acid metabolism most active?
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)
what occurs during short term starvation where there is an absence of fatty acids to feed into the TCA or glucose:
•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
what molecules are crucial in transporting amino groups around the body?
glutamate and alanine
what is the major amino acid found in muscle?
the major amino acid in muscle protein is the branched chain amino acid (BCAA) LEUCINE
what happens to muscle during periods of fasting?
during periods of fasting, skeletal muscle protein is degraded into its amino acid constituents
what is always taking place in the muscle?
there is always glycolysis occurring n the muscle
If there are supply of BCAA in our diet and if they are present in the plasma…
muscles use them as fuel resulting in ammonia ions which are stored in forms of glutamate, glutamine and alanine
what is the glucose-alanine cycle primarily a mechanism for?
it is primarily a mechanism for skeletal muscle to eliminate nitrogen while replenishing its energy supply
what is alanine fuel for?
alanine is fuel for gluconeogenesis (via pyruvate) in the liver to produce glucose which is transported back to the muscle
where can glutamine come from?
glutamine can come from anywhere in the body
how do most other tissues (non-muscle-tissue) break down protein as a fuel source without using glucose?
most other tissues use amino acid deaminases to catabolise amino acids to provide the carbon skeletons as a fuel source
the many uses for amino acids within the body:
•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)
amino acids as building blocks for hormones:
•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
Glutamate is decarboxylated into the GABA neurotransmitter:
•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
tyrosine is important for maintaining neuronal signalling:
•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
