Amino Acids Flashcards
What are the sources for amino acids?
dietary proteins
Where does protein degradation occur?
-begins in the stomach as only mono-/di-/tripeptides can be absorbed through the intestines.
What is pepsin?
-a protease in the stomach active at pH=2. Must be activated from pepsinogen
What two ways can nitrogens be removed from the amino acids?
- deamination
- transamination
What happens in the intestines with protein digestion?
pH change inhibits pepsin activity
- aminopeptidases continue digestion
- variable transporters absorb the 1,2,3 amino acids components
What are able to degrade proteins?
- proteasomes
- lysosomes
What signals proteasomes for protein degradation?
- ubiquitin tag
- the C-terminal Gly binds with the proteins’ Lys residue covalently
What are the enzymes for ubiquitin facilited protein degradation?
- E1: ubiquitin activating
- E2: ubiquitin conjugating
- E3: ubiquitin-protein ligase
The nitrogen balance in the body directly affects the protein turnover. What happens in + nitrogen balance?
- nitrogen intake is higher than excretion and is seen in athletes and early development
- could be seen my increased urine urea levels
The nitrogen balance in the body directly affects the protein turnover. What happens in - nitrogen balance?
The nitrogen intake is less than the nitrogen degradation
- less urea in the urine
Proteolysis is the process of peptide fragment degradation and results in what?
- amino acids
- process occurs in cytoplasm of cells
The amino acids have a few choices of where they can go in the body. What pathways can they engage in?
- remain intact for biosynthesis
- contribute to nitrogen excretion via the urea cycle
The carbon skeleton of the amino acids can go down what pathways?
- glucose or glycogen synthesis
- cellular respiration
- fatty acid synthesis
What is the big picture with ammonium formation?
- occurs in the liver
- N from any 20 AA form glutamate, and then form ammonium and then into the urea cycle
What does aminotransferase do and how does it do it?
- transfers the NH2 from alpha AA to glutamate
- requires co-factor (pyradoxil-5-phosphate) generated from Vit B6
What does glutamate dehydrogenase do and what cofactors are required?
- Causes oxidative deamination to form ammonium ion, which can then enter the urea cycle to form urea and be excreted.
- process occurs in liver to protect nervous system
- requires NAD+ derived from niacin derived from Vit B3
What organ is the urea cycle specific to and why?
-the liver as ammonium is toxic to nervous tissue
What is carbamoyl phosphate synthetase I?
rate limiting enzyme for
CO2 + NH4—> carbamoyl phosphate
What is ornithine transcarbamoylase?
-converts ornithine, carbamoyl phosphate to generate citrulline in the urea cycle
What is argininosuccinate synthase?
- converts citrulline to argininosuccinate
- intermediate that could move to form fumarate and OAA to gluconeogenesis
What is argininosuccinase?
-enzyme that converts argininosuccinate to arginine in urea cycle
What is Arginase?
- enzyme that regenerates ornithine from arginine
- also releases urea
The brain is sophisticated and has methods to remove toxic NH4 ion from its environment. What type of effects does this have on the brain?
- NH4 ion is removed in the brain as glutamine which can then enter the urea cycle
- the process requires NADPH and ATP, which burns extra energy that the brain would have utilized better.
How have muscles developed to remove the nitrogen from their system?
-the muscles generate Ala in order to transfer the N to the blood and to the liver.
