Amino Acid Metabolism Flashcards
Describe the two sources from which proteins are able to be introduced to the body
Diet and Intracellular
Describe the various proteins that are located in the stomach and the small intestine and briefly say what they do
The stomach has pepsin that thrives in low pH environments and cleaves proteins
the small intestine has enteropeptidases which cleaves trypsinogen; amino peptidases which chew from the N end, and dipeptides that break apart dipeptides
What are the two structures that can degrade proteins?
The proteasome
The lysosome
Describe ubiquitin and how it works to lead to protein degradation
The N-end determines the rate of ubiquination and the size of the half life
Ubiquitin binds to the proteasome and essentially brings the targeted protein to the proteasome for degradation. The ubiquitin can be recycled
-can also be involved in protein recycling, factor recruitment, and disruption of interactions
Describe the proteasome including the definition of “S” in the subunits
ATPase
26S proteasome consists of a 20S(catalytic) subunit and a 19S(regulatory) subunit
S stands for Svedberg sedimentation and is influenced by numerous factors
Describe how the proteins are able to get to amino acid form in degradation
Ubiquinated and taken to the proteasome where it is broken into peptide fragments and the ubiquitin is released. The fragments are degraded further by cytosolic proteases (produced in proteasome) leaving amino acids
Describe the 3 possible fates of the amino acids (reduce, reuse, recycle)
- reduced: can get rid of the amine group via the urea cycle
- Reuse: make new proteins
- Repuprose the carbon skeleton (make other intermediates for other metabolic pathways)
Describe the process of deamination. What do “MOST” amino acids do?
Separates the NH3 from the alpha carbon, leaving behind the carbon skeleton;
MOST amino acids follow a 2 enzyme mechanism: aminotransferase and glutamate dehydrogenase
Describe the deamination of serine and threonine and describe the differences
Involves a direct deamination via a dehydration reaction
- H20 is removed
- This is used to remove the NH4+ group
serine forms a pyruvate
threonine forms alpha-ketobutyrate
Describe the deamination to make glutamate
an amino acid and alpha ketoglutarate are combined and exposed to an aminotransferase that transfers the amino group of the amino acid to the alpha-ketoglutarate to make an alpha ketone acid (the amino acid post deamination) and glutamate (NH3+alpha ketoglutarte)
Describe the two “special” aminotransferases
- aspartate aminotransferase (AST)/ Serum Glutamate Oxaloacetate Transaminase (SGOT):
interconversion of aspartate and oxaloacetate - alanine aminotransferase (ALT)/ Serum glutamate-pyruvate transaminase (SGPT): interconversion of alanine and pyruvate
Describe how the amine group (NH3) is able to be derived from glutamate
Glutamate dehydrogenase is able to release the NH3, with the help of NAD+ or NADP+, which forms a Schiff base that is able to be hydrolyzed to alpha-ketoglutarate which releases NH4+
Describe what happens with the excess NH4+
It is converted into urea in the liver, which is able to be transported to the kidneys and be yeeted out
Describe how most tissues are able to get rid of their excess NH4+ and excrete it in the urine
- glutamine synthetase adds the NH4+ to glutamate that is in the tissues to make glutamine.
- the glutamine is able to travel through the blood to the liver
- Glutaminase removes the NH4 from the glutamine to make glutamate with the help of H2O
- The free NH4+ is able to be made into Urea
Describe how the muscle tissue is able to get rid of excess NH4+ via the urea cycle
- NH4+ from amino acids can be added to glutamate
- glutamate can release alanine during the formation of alpha-ketoglutarate
- Alanine can also be created from glucose via glycolysis
- Alanine can be transported to the liver via the glucose-alanine cycle
- alanine can be reformed into glutamate, which can release the NH4+ in the liver with the help of glutamate dehydrogenase
- urea cycle baby
What are the 4 pieces that compose urea?
- H2O
- carbamoyl phosphate
- aspartate
- bicarbonate
Describe the committed step in the urea cycle
Carbamoyl phosphate synthetase I (CPSI) combines CO2 and NH3 to make carbamoyl phosphate with the help of 2 ATP
Describe the regulation of carbamoyl phosphate synthetase I
CPSI is stimulated by NAG (NAG is activated when there are amino acids in excess)
CPSI is inhibited when there is a decrease in ammonia secondary to acetylation
NAD+ is able to deacetylate and activate the enzyme
Describe the second step of the urea cycle (carbamoyl phosphate has already been made)
Carbamoyl phosphate is added to orthinine and forms citrulline with the help of orthinine transcarbamoylase
*** happens in the mitochondrial matrix
After citrulline is made, it is transported to the cytoplasm. Describe the next 3 steps of the urea cycle that occur in the cytoplasm
- citrulline is added to aspartate and turned into argininosuccinate with the help of argininosucinate synthetase
- argininosuccinate is broken down into arginine and fumarate with the help of argininosuccinase
- arginine is broken into ornithine and urea with arginase
Describe how the urea cycle is linked to gluconeogenesis
Fumarate, which is a product following exposure to argininosuccinase.
Fumarate is able to be turned into malate, which can be turned into oxaloacetate which can be turned into glucose via gluconeogenesis
How much of the liver’s ATP consumption does the urea cycle take up
50% is used to make the average 30g of urea
List the 7 possible fates of amino acids and state if they are glucogenic or ketogenic
- pyruvate: STCAG: They are all glucogenic
- Oxaloacetate: AA (asparagine and aspartate) they are glucogenic
- alpha-ketoglutarate: RQHEP (“real queens hump every penis); glucogenic
- Succinyl CoA (Meth and Vaping Succ) methionine and valine are glucogenic and Isoleucine is “both”
- Fumarate: glucogenic because it can be directly converted into glucose
- acetyl CoA; ketogenic
- acetoacetate: ketogenic
