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AA metab, Urea

Biochem - Protein and AA Metabolism and The Urea Cycle

QuestionAnswer
AA catabolism produces what toxic product? Ammonia
What are the essential amino acids? PVT TIM HALL(phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, arginine, lysine, leucine)
What are the two possible sources of essential amino acids? diet, protein turnover
What are some products that are made from amino acids? Carbon (synthesis of glucose, fatty acids, ketones and energy)Nitrogen (urea)Synthesis of other N-containing molecules (purines, pyrimidines, porphyrine (bilirubin), neurotransmitters)
What is negative nitrogen balance? When input is less than output. Endogenous amino acids are being broken down, thus "excreting" and is more than is being taken in.
When does negative nitrogen balance occur? Dietary Deficiency (starvation)Catabolic stress (ex. infection)
What is positive nitrogen balance? When input is greater than output. You are taking in more nitrogen than you are excreting.
When does positive nitrogen balance occur? Childhood (growth)Pregnancy
What is tyrosine synthesized from? Phenylalanine
What does phenylalanine synthesize? Tyrosine
What 3 cofactors are required for amino acid synthesis? Pyridoxal phosphateTetrahydrofolateTetrahydrobiopterin (BH4)
Can essential amino acids be synthesized by the body? NO!
When pyruvate is transaminated, what does it synthesize? Alanine
When oxaloacetate is transaminated, what does it synthesize? Aspartate
When alpha-ketoglutarate is transaminated, what does it synthesize? Glutamate
What forms alanine by transamination? Pyruvate
What forms aspartate by transamination? Oxaloacetate
What forms glutamate by transamination? alpha-ketoglutarate
Where is arginine generated? Urea cycle
Where does Cysteine get its S? Methionine
Can some enzymes used in amino acid synthesis also be used in amino acid degradation? YES! example: transaminases
What is pyridoxal phosphate (PLP) synthesized from? Vitamin B6
What are two mechanisms through which nitrogen is removed from amino acids? TransaminationDeamination
What is deamination? Where an amino group is removed. This results in ammonia production.
What is transamination? Where an amino group is transferred to another molecule. This does NOT result in ammonia production. Most cells do this (rather than deamination)
What do alpha-ketoglutarate and glutamate do in transamination? Alpha-ketoglutarate accepts the amino acid in transamination, which causes the formation of glutamate.
What is another name for aminotransferases? Transaminases
What is another name for transaminases? Aminotransferases
What do transaminases/aminotransferases require as a cofactor? PLP
Is transamination reversible? YES!
Why is it important that transamination be reversible? It enables the same enzymes to be used in amino acid degradation and amino acid synthesis.
The direction of a transaminase reaction will reverse in response to ... changes in concentration.
What does ALT catalyze? Pyruvate --> alanine
What enzyme is involved in the pyruvate --> alanine reaction? ALT
What does AST catalyze? Oxaloacetate --> aspartate
What enzyme is involved in the oxaloacetate --> aspartate reaction? AST
What do high ALT and AST levels indicate? Liver damage, because they are released into the plasma (thus showing up as high levels in the blood). You will also see low albumin levels in the blood, because albumin is the most abundant protein synthesized in the liver.)
What is the function of glutamate dehydrogenase? It deaminates glutamate, resulting in alpha-ketoglutarate and ammonia.
Where does the deamination of glutamate by glutamate dehydrogenase take place? Liver
What enzyme is involved in the deamination of glutamate into alpha-ketoglutarate and ammonia? glutamate dehydrogenase
What enzyme is involved in the conversion of glutamate + ammonium (NH4+) --> glutamine Glutamine synthase
What conversion does glutamine synthase catalyze? glutamate and ammonium --> glutamine
How many ammonia molecules does glutamine have? two
What enzyme is involved in the conversion:glutamine --> glutamate + NH4+? Glutaminase
What does glutaminase do? Removes an ammonium from glutamine to create glutamate.
What transport role is alanine important in? Transporting ammonia to the liver.
How are pyruvate and ALT involved in the transport of ammonia to the liver? Pyruvate is transaminated into alanine by the ALT enzyme. Once in the liver, alanine gives the amino group back to glutamate (and thus converting back to pyruvate - which can be used for gluconeogenesis).
What defines glucogenic amino acids? Can create glucose.Ultimately degraded to pyruvate or TCA cycle intermediates.
What defines ketogenic amino acids? CANNOT make glucose.Ultimately degraded to Acetyl CoA or acetoacetate.
What is the effect of insulin on amino acid metabolism? Promotes amino acid uptake and protein synthesis.Pure protein meal stiumlates insulin secretion but much less than a carb meal would.
What is the effect of cortisol on amino acid metabolism? Stimulates uptake of amino acids into the liver.Induces ubiquitin synthesis.Stimulates gluconeogenesis so amino acids are needed to provide precursors.
What is the effect of glucagon on amino acid metabolism? Stimulates uptake of amino acids into the liver.
Do insulin, cortisol, and glucagon stimulate the uptake of amino acids into the liver? YES!
In the FASTED state, what do the liver and muscles contribute to amino acid metabolism? Muscles = provide amino acids for metabolismLiver = uses lots of amino acids in fasted state
What is a hypercatabolic state? State of increased fuel usage.Negative nitrogen balance.Cortisol is a mediator.Ex. defense against infection/wound healing
Where does the urea cycle occur? Liver
What is the enzyme that converts HCO3- + NH4+ --> Carbamoyl phosphate? CPS1 (carbamoyl phosphate synthase 1)
What is the rate limiting step in the urea cycle? CPS1 (carbamoyl phosphate synthase 1)
What is the enzyme that converts Ornithine to Citrulline? OTC (ornithine transcarbomylase)
Where do the two N's in urea come from? One from ammoniaone from aspartate
What is the common source of both of the N's in urea? Glutamate
Where do the first two steps of the urea cycle occur? Mitochondria
In the urea cycle, after the first two steps, where do the following steps occur? Cytoplasm
What are two products from the urea cycle? arginine fumarate
Is ornithine regenerated? YES!
Is the process of urea formation irreversible? YES!
What is the rate limiting step of the urea cycle? CPS1
How is the urea cycle regulated? Feed forward process(substrate availability)
Does CPS1 have an allosteric regulator? YES!
What is the role of NAG in the urea cycle? It is synthesized by acetyl CoA and glutamate and it STIMULATES CPS1
What is the fate of urea? Can cross membranes and is filtered into blood.Then, filtered by kidneys and excreted in urine.Some urea diffuses into intestines and is cleaved by bacteria.
What is BUN? Blood Urea Nitrogen, measure of urea concentration in blood.
What does an elevated BUN show? kidney failure
What does a low BUN show? liver disease
How does diet affect BUN? more protein in the diet will show higher BUN levels.
What is hyperammonemia? Increased ammonia levels in the blood.Caused by liver disease or kidney failure (more urea metabolized by intestinal bacteria = incr. BUN)
Ornithine transcarbamoylase deficiency (OTC), the most common cause of urea cycle disorder, is what type of genetic trait? x-linked.
Created by: kbb135 on 2008-12-01



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