Metabolism III: Protein Flashcards
Can amino acids be synthesized de novo?
Yes, but nitrogen has to come from the environment
Where are all AAs derived from?
intermediates in:
glycolysis
CAC
PPP-pyruvate
Nitrogen enters the pathways by way of…
glutamate and glutamine
How many AAs can plants and bacteria synthesize?
all of them
How many AAs can mammals synthesize?
only about half of them
What are the fates of carbon skeletons?
- ketogenic AAs
- Glycogenic AAs
- Gluco- and ketogenic AAs
How can AAs be classified?
- essential vs nonessential
- fate of C skeleton
- hydrophobic vs hydrophilic
AAs as a source of energy
humans derive a small fraction of their oxidative energy from the catabolism of AAs
What are the three AA metabolic states?
- protein turnover
- dietary protein
- during starvation and uncontrolled diabetes
What happens to AAs during protein turnover?
Was released from breakdown of cellular proteins
What happens to AAs during dietary protein?
- Surplus AAs undergo oxidative degradation
- they cannot be stored
What happens to AAs during starvation?
Muscle protein broken down to release AAs
What happens to AAs in uncontrolled diabetes?
Carbohydrates are not properly utilized
The AAs lose their amino groups to form what during metabolism?
a-keto acids (the carbon skeletons of AAs_
What are the two metabolic fates of a-keto acids?
- undergo oxidation (Krebs) to CO2 and H2O
- provide 3 and 4 carbon units that can be converted by gluconeogenesis into glucose
Where do the processes of AA degradation converge?
Krebs cycle
What four AAs play a central role in AA metabolism?
- glutamate (a-KG)
- glutamine (a-KG)
- alanine (pyruvate)
- aspartate (oxaloacetate
What are the two major biochemical processes that occur during AA catabolism?
- transamination
- deamination
What is the enzyme involved in the process of alanine-glucose cycle?
alanine aminotransferase
What is the enzyme involved in the process between a-KG and glutamate?
valine aminotransferase
Where does transamination of alanine-glucose cycle occur?
- muscle
- Cytosol of liver
What AA metabolism occurs during transamination in the muscle?
alanine- glucose cycle
What is the reaction that occurs during alanine-glucose cycle?
Glutamate + pyruvate –> alanine + aKG (pyruvate)
What does the alanine do in the alanine-glucose cycle?
- alanine transports ammonia from skeletal muscle to liver
What is the alanine-glucose cycle in concert with?
Cori cycle
What happens to pyruvate and lactate during the alanine-glucose cycle?
- transported to liver for gluconeogenesis
- ammonia converted to urea in liver
- energetic burden is imposed on liver and not muscle
Where does deamination occur?
mitochondria of liver
What is the reaction of deamination?
glutamate –> Ammonia + aKG
Where does the ammonia in deamination go?
urea cycle
Where does aKG go in deamination?
Krebs cycle
gluconeogenesis
What enzyme is used in the conversion of glutamate + ammonia to glutamine?
Glutamin synthetase
What is the enzyme used in the conversion of glutamine to glutamate?
Glutaminase
What organ is more susceptible to ammonia toxicity?
Brain
What occurs during the mechanisms of ammonia?
molecular mechanism is unclear
What are the terminal states of ammonia intoxication in humans characterized by?
- comatose state
- cerebral edema
- increased cranial pressure
What is the major acceptor of ammonia?
- glutamate (forms glutamine)
- this will deplete glutamate
Glutamate and its derivative (gamma-aminobutyrate) are important …
NTs
What happens to the free ammonia produced in the extra-hepatic tissues?
converted to a non-toxic product
What AA is affected in albinism
melanin synthesis from tyrosine
What AA is affected in alkaptonuria?
Tyr degradation
What AA is affected in maple syrup disease?
(branched chain ketoaciduria)
Iso, Leu, Val degradation
What AA is affected in phenylketonuria?
conversion of Phe to Tyr
