Week 10 - Protein Metabolism Flashcards
Define the amino acid pool
aa in blood + extracellular fluids
How much protein in kg does the body of a 60kg woman have?
+ how much of free aa (g)
60kg woman:
- 10kg protein
about 170g of free aa
Define non-essential/dispensable aa
aa synthesised by liver to make body proteins
Define essential/indispensable aa
aa that can’t be synthesised so must be obtained in diet.
Can some non-essential aa become indispensable? why?
yes
if they’re not prod at a fast enough rate.
What happens to the aa synthesised in the liver
Used in liver or released into blood
Whats left after an aa loses their amino group?
Carbon skeleton
What can happen to the carbon skeleton?
Oxidised directly
Used to make glucose in gluconeogenesis
Converted into fat for storage
Why do aa need protein transporters to move them?
Because of their charged groups
What are the types of protein transporters for aa
Sodium ion dependent
Sodium independent
Sodium ion dependent transporters
Symport transport system in which aa moves into cell down Na+ conc. grad + can be moved vs their conc. grad
Define transamination
1 aa is changed to another by the transfer of an amino group
Can humans use the N in the amino groups as an energy source?
NO, so most is excreted.
How are carbon skeletons very valuable?
Can become intermediates for the TCA cycle
When will aa undergo constant oxidative degradation?
During normal synthesis + degradation of proteins.
When we ingest more aa than our bodies need
During starvation, fasting, dieting or uncontrolled diabetes mellitus
When we overtrain
NUTRITIONALLY NON-ESSENTIAL OR ESSENTIAL
Alanine
NUTRITIONALLY NON-ESSENTIAL
NUTRITIONALLY NON-ESSENTIAL OR ESSENTIAL
Histidine
ESSENTIAL
NUTRITIONALLY NON-ESSENTIAL OR ESSENTIAL
Leucine
ESSENTIAL
What are the 2 major stages of catabolism of ind aa
- Lose N atoms as can’t obtain usable energy from the N groups.
- Resulting carbon skeletons are fed into specific energy-yielding pathways so that their chemical energy can be retrieved.
What organ removes the amino groups from most aa
Liver
What has a significant capacity for deamination of the BCAAs (branched-chain amino acids)
Skeletal muscle
What aa can’t undergo transamination reactions?
Threonine + lysine
NUTRITIONALLY NON-ESSENTIAL OR ESSENTIAL
Asparagine
Non-essential
NUTRITIONALLY NON-ESSENTIAL OR ESSENTIAL
Lysine
Essential
NUTRITIONALLY NON-ESSENTIAL OR ESSENTIAL
Glycine
Non-essential
NUTRITIONALLY NON-ESSENTIAL OR ESSENTIAL
Proline
non-essential
What vitamin does aminotransferase contain
Vitamin B6
What is the typical reaction for aminotransferase
Transfers an amino group to α-ketoglutarate to make glutamate + a new carbon skeleton in the form of a keto acid:
α-ketoglutarate + aa – (aminotransferase) – > glutamate + α-keto acid.
What is vitamin B6 a precursor for?
Coenzyme pyridoxal phosphate
Are transamination reactions reversible or irreversible?
Freely reversible
Their net direction depends on the rel conc of the reactants
In deamination, where can the amino groups be shuttled from?
1 aa to α-ketoglutarate to make GLUTAMATE
Glutamate to another keto acid to create a NEW AA
Where must the amino group on glutamate be transferred to (if not already there) + what happens to it there
To liver + into the creation of the urea mol.
What happens in the glutamate dehydrogenase reaction?
Removes N from glutamate which can then be used to make urea.
In the liver
Is the glutamate dehydrogenase reaction reversible?
YES, freely reversible
Where does the glutamate dehydrogenase reaction take place
In the mit matrix
Where can most aminotransferase enzymes be found?
Mit matrix + cytosol
What type of reaction is the glutamate dehydrogenase reaction as it proceeds to the right
A deamination reaction as it removes the amino group
When does the glutamate dehydrogenase reaction become an oxidative deamination reaction?
NAD+ –> NADH
What is the relationship between the prod of ammonium ion + its release from muscle?
Proportional to the intensity of the exercise.
What % of the aa pool is glutamine?
60
Where does glutamine come from?
Some diet
Most synthesised in body from glutamate using glutamine synthetase.
What is glutamine fuel for
Gut + immune system
Wheres an important site for glutamine synthesis ?
Skeletal muscle
But also prod in brain, adipose tissue + heart.
What is the reverse reaction of the glutamine synthetase reaction?
Removal of the amino group from the side chain of glutamine.
What reaction does glutamine synthetase catalyse?
Glutamate + ATP + NH4+ –> ADP + Pi + Glutamine
Where can glutaminase be mainly found
Liver mitochondria
What does glutaminase catalyse the reaction of?
Deamination reaction:
Glutamine + H20 –> Glutamate + NH4+
Give examples of BCAA
Leucine
Isoleucine
Valine
Where are BCAAs metabolised?
Mainly in skeletal muscle but can also be metabolised in liver.
After the 1st 3 reactions of the catabolism of BCAAs what happens next?
- Valine + isoleucine produce succinyl CoA.
- Leucine catabolises –> acetoacetate + Acetyl CoA which can’t be converted to glucose, so leucine is considered a ketogenic aa.
What happens in the 1st reaction of the catabolism of the BCAAs
Transamination
= in which the amino group is transferred to α-ketoglutarate to make GLUTAMATE.
Whats different about the BCAA aminotransferase enzyme compared to the aminotransferase enzyme in transamination reactions
Aminotransferase in freely reversible transamination reactions.
BCAA aminotransferase goes only 1 way.
Why does BCAA aminotransferase work only one way
Due to products undergoing an oxidative decarboxylation catalysed by BCKAD (Branched-chain ketogenic acid dehydrogenase).
What does the alanine aminotransferase enzyme do?
Can transfer the amino groups on the BCAAs rom glutamate to pyruvate
What are the 2 safer temporary forms of ammonia
Amino group of glutamate
Side chain amide N in glutamine
Where is urea formed
Liver
Where is urea excreted from
kidney when urine is formed
Where does the carbonyl group on urea come from
CO2
Urea synthesis req ammonium ions coming from where?
Ammonia taken up by the liver from the blood
From glutamine via the glutaminase reaction
From glutamate via the glutamate dehydrogenase reaction.
Where does aspartate come from?
Transamination reaction
= in which oxaloacetate undergoes transamination from glutamate to make aspartate + a-ketoglutarate
