Protein Turnover And Amino Acid Catabolism(Week 4) Flashcards
(28 cards)
Give three sources of amino acids.
Ingested in the diet
Turnover of endogenous proteins
De novo biosynthesis
Give three uses of amino acids
Protein synthesis
Nitrogen and carbon source of general and special product biosynthesis
Energy source
What types of organisms oxidise amino acids to give energy
Carnivores. Not herbivores or plants
What are the three circumstances where amino acids undergo oxidative degradation.
Normal synthesis and degradation of excess cellular proteins.
When a protein rich diet exceeds the body’s need for protein, the surplus is stored as glucose, glycogen or fats as amino acids cannot be stored
During starvation or uncontrolled diabetes.
Where does amino acids catabolism occur?
The liver
What happens in the liver with regards to amino acid catabolism
Excess amino groups are transferred to alphaketoglutarate to form glutamate.
What happens in skeletal muscles with regards to amino acid catabolism
Excess amino groups are transferred to pyruvate to form alanine, which is then converted to glutamate.
What happens in all other tissues with regards to amino acid catabolism
Excess amino groups are transferred to the R-group of glutamine then converted to glutamate
Why are glutamate and glutamine important for nitrogen metabolism
They act as a general collection point for amino groups
Essential amino acids cannot be synthesised and need to be obtained in the diet. What are the 9 essential amino acids?
Histidine Isoleucine Leucine Methionine Phenylalanine Threonine Valine
What causes acute pancreatitis?
The zymogens of the proteolutic enzyme are converted to the active forms prematurely, attacking the pancreatic tissue.
Protein turnover needs to be tightly regulated. What is the protein which tags other proteins for distraction?
Ubiquitin
Give an overview of how ubiquitin attaches to the protein.
Attach AMP Attach E1 Attach E2 Bind to E3 and get close to the target Attach to target
What can a defective E3 enzyme cause?
Protein aggregation
What is the specific amino acid sequence called which determines the half life of proteins?
Degrons
What is the role of theE3 enzyme?
To read the N-terminal residues.
What machine causes the ‘death’ of proteins, and what is its structure?
The 20S proteasome. It is comprised of 28 homologous subunits arranged on four rings of seven subunits each.
What are the functions of the 19S complex?
Detect ubiquitin
Cleave off intact UBQ
Unfold the ‘doomed’ protein
What is the first step in amino acid degredation
Transamination reaction.
This form glutamate and a carbon skeleton.
What is the second step in amino acid degradation?
Oxidative deamination of glutamate. This forms ammonium ions.
Glutamate dehydrogenase, releases NH4+. Glutamate dehydrogenase uses NAD+ or NADP+. This sequesters a free ammonium ion which is toxic.
What happens to the NH4+ ions?
The peripheral tissues transport nitrogen to the liver.
NH4+ + glutamate + ATP = glutamine + ADP + Pi.
This uses the glutamine synthesise enzyme.
What cycle allows branches amino acids to be broken down in the muscle?
The glucose adenine cycle.
What do the enzymes aminotransferases do?
Use transaminition reactions to make glutamate.
What does the enzyme glutamate dehydrogenase do and where is it found?
In the liver.
Used to make ammonium and NAD(P)H, as well as regenerating alpha-ketoglutarate.
