Protein turnover and amino acid metabolism Flashcards
What is the first step in amino acid degradation?
The removal of nitrogen
What does ubiquintin and polyubiquintin do?
Ubiquintin is a small highly conserved protein that tags proteins for destruction
Polyubiquintin is an especially effective destruction system
What is the proteasome and describe the structure of one
The proteasome is a large molecular complex of proteolytic enzymes that degrades ubiquintinated proteins
The 26s proteasome consists of two components, a 20s catalytic subunit and a 19s regulatory subunit
What does the regulatory subunit do?
It binds to the polyubiquintin, cleaves off the intact ubiquintin, unfolds the unwanted protein and inserts it into the catalytic subunit
Where is the main site or amino acid metabolism and what are its possible gates
The liver
They can become building blocks for bio synthetic reactions
Or
Degradation to other molecules that can enter metabolism
What is the remaining carbon skeleton metabolised to?
Glucose
A citric acid cycle intermediate
Acetyl CoA
What do transaminases do
They catalyse the transfer of an a-amino group from an amino acid to an a keto acid
What are transamination reactions used for?
To synthesise amino acids from a-ketoacids
They’re reversible reactions
What happens in the oxidative deamination of glutamate?
The nitrogen atom in glutamate is converted into a free NH4 ion by oxidative deamination
Glutamate dehydrogenase releases NH4 in the oxidative deamination of glutamate
What is the overall reaction for formation of ammonium ions from amino acids?
a-amino acid + NAD+ +H20——> a-ketoacid +NH4+NADH+H+
< —
What is the first step in the urea cycle?
The coupling of ammonia with bicarbonate
What catalyses the reaction in the first step of the urea cycle?
Carbamoyl phosphate synthase
It is the committed reaction of the urea cycle
What happens in the first stage of the complex reaction in urea synthesis?
In the cytosol, Citrulline condenses with aspartate (The donor from the second nitrogen of urea) to form argininosuccitate
This reaction is driven by the hydrolysis of ATP into AMP and pyrophosphate
What happens in the second stage of the complex reaction in urea synthesis?
Argininosuccitate is cleaved into arginine and fumerate by argininosuccinase.
The synthesis of Fumerate is important as it is a precursor of glucose
What happens in the third stage of the complex reaction in urea synthesis?
Arginine is cleaved by arginase into urea
Urea is excreted and orinthne is transported into the mitochondria
