Topic 16 - Amino Acid Metabolism Flashcards
All amino acids contain ….. which exists in 3 forms. These forms are ……., ……… and ……….
These forms are interconverted in the ….. cycle
All amino acids contain nitrogen, which exists in 3 forms.
These forms are unfixed (gaseous), inorganic (NH4+) and organic (aa).
These forms are interconverted in the nitrogen cycle.
Describe the nitrogen cycle
- Unfixed N2 => fixed NH4+ by n-fixing bacteria & algae
- Fixed N NH4+ used by plants to form aa/proteins
- aa consumed by animals
- animals excrete excess N into enviro as ammonia in urea
Give a brief overview of aa metabolism
- aa metabolism involves seperating amino group from carbon group, which is achieved by amination, deamination & transamination reactions
Describe Amination
- Glutamine synthetase catalyses addition of ammonium onto glutamate to form glutamine
- Results in temporary amination to allow transport of ammonium in blood as glutamine (NH4+ is toxic)
- In liver, NH4+ is re-released by glutaminase, & disposed of in urea
Describe Deamination
- Reverse of amination
- Two important enzymes:
- 1. Glutaminase (liver, kidney cortex)*
- Removal of ammonia from glutamine reforming glutamate (ammonium => urea in liver)
- Ammonia produced derived from amide N of glutamine (side chain)
- 2. Glutamate DH (liver)*
- Removal of amino group from glutamate to form a-keto glutarate & ammonium
- Rxn is reversible, equilibrium constant favours deamination rxn
Describe Transamination
- aa transfers its amino group to a-keto glutarate & is converted to an a-keto acid
- Glutamate formed
- No net deamination (loss of amino group) -a-keto g is aminated; aa deaminated
- For most aa there is a specific aminotransferase that transfers amino group onto a-keto g
- Rxn readily reversible
- All amintransferases need pyridoxal phosphate (PLP) as a cofactor
Describe amino acid catabolsim -in 4 easy steps!
When is it a major energy source?
- Is NOT a major energy source under NORMAL conditions
- Significant under 3 conditions:
- **-dietary protein ingested in excess
- severe starvation
- stress situations***
- Catabolism in 4 easy steps!
-
1.* catabolism of protein w/in muscle results in formation of aa’s **glutamine & alanine
2. **Transport of Glu & Ala into blood - Ala => liver
- Glu => liver & kidney
- 3. Kidney -* Glu deaminated twice => a-keto g. Ammonium excreted in urine. C skeleton used in glucose formation
- 4. Liver -* Ala & Glu from muscle, & all 20 aa from diet are deaminated => glutamate. C skeleton => glucose or ketone body. Glutamate deamin. in mitochondria & NH4+ converted to urea. Urea => liver => blood => kidney => excretion
DRAW THE DIAGRAM THAT SUMMARISES AA CATABOLISM
Remember to include:
Where there us organic or inorganic N
transamination rxns
deamination rxns
PLP
Where NH4+ is produced/released
muscle/kidney/liver cell section
mitochondria cell section
Don’t forget extra labels written in lecture
Brief overview of C skeleton degradation?
Glucogenic aa - c skeleton fed into GNG pathway
Ketogenic aa - c skeleton used to make ketone bodies
aa syntesis -essential and non-essential aa’s?
- Humans and animals can catabolise all 20 aa, but not all possess the pathways to synthesise all 20 aa’s
- Animals typically cannot synthesise 8-12 of the aa & must obtain them from diet. These are called essential amino acids
- Humans can only synthesise 10 aa. These are called non-essential amino acids as they are not essential in the diet
- PLP
- liver
- Very low CHD, very high protein
- Glutamine and alanine
