Metabolic pathways: amino acids Flashcards
Are all amino acids be converted to acetyl-CoA?
No, but all amino acids can be oxidised in the TCA cycle
Can amino acids be stored in the body?
No, any amino acid that is not involved in protein synthesis has to be degraded
Where are amino acids that are not used in protein synthesis degraded?
Liver
Where do the amino acids for degradation come from?
Mostly from diet
Protein turnover
What happens to proteins/amino acids in the stomach and small intestine?
Proteolytic enzymes break proteins into single amino acids, and di- and tri- peptides
These are absorbed into intestinal cells and released into blood for absorption by other tissues
What is the main problem for amino acid breakdown?
Amino acids contain nitrogen - in amino groups and sometimes in side chains
The breakdown of amino acids produces ammonia and ammonium ions which can be toxic
What is the main molecule for excreting nitrogen from amino acid metabolism?
Urea
Where is urea formed?
Liver
How much of the nitrogen from amino acid breakdown is excreted by urea?
80%
What is the first step of urea synthesis and what does this involve?
Transamination
An amino group from an amino acid is transferred onto a keto acid, forming a new amino acid and a keto acid
What is the second step of urea synthesis and what does this involve?
De-amination
The amino group is removed from the newly formed amino acid, releasing a free ammonium group and an NADH
What happens to the free amino group produced in the second step of urea synthesis?
It enters the urea cycle, where it is converted to urea
How many nitrogens does urea contain and where do they come from?
2
One from the de-amination of an amino acid forming a free ammonium ion
Another from aspartic acid
Where does transamination occur?
In all tissues
Where does de-amination occur?
Liver
What must happen to the glutamate (newly formed amino acid from transamination) for it to be transported to the liver?
Amino group of glutamate is transferred to pyruvate
OR
Glutamine synthase adds NH4 to glutamate, giving glutamine
What is the most common amino acid involved in transamination of urea synthesis?
Usually alpha-ketoglutarate receives an amino group from the alpha-amino acid to form glutamate
What are the major carries of nitrogen in blood to the liver?
Glutamine
Alanine
Where is the carbon in urea derived from?
CO2
How many ATP are cleaved to allow urea synthesis?
3
What happens to the carbon skeletons left after the removal of alpha amino groups?
Converted to major metabolic intermediates
e.g. can be converted to glucose or oxidised in the TCA cycle
What are ketogenic amino acids converted into?
Degraded to acetyl-CoA or acetoacetyl-CoA
Can give rise to ketone bodies or fatty acids
What are glucogenic amino acids converted to?
Degraded to pyruvate or TCA cycle intermediates
Can be converted into phosphoenolpyruvate and then into glucose
What is alcaptonuria?
A disorder in which the degradation of phenylalanine and tyrosine is blocked
