Biochem - Protein and AA Metabolism and The Urea Cycle
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| AA catabolism produces what toxic product? | Ammonia
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| What are the essential amino acids? | PVT TIM HALL(phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, arginine, lysine, leucine)
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| What are the two possible sources of essential amino acids? | diet, protein turnover
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| 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)
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| 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.
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| When does negative nitrogen balance occur? | Dietary Deficiency (starvation)Catabolic stress (ex. infection)
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| What is positive nitrogen balance? | When input is greater than output. You are taking in more nitrogen than you are excreting.
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| When does positive nitrogen balance occur? | Childhood (growth)Pregnancy
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| What is tyrosine synthesized from? | Phenylalanine
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| What does phenylalanine synthesize? | Tyrosine
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| What 3 cofactors are required for amino acid synthesis? | Pyridoxal phosphateTetrahydrofolateTetrahydrobiopterin (BH4)
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| Can essential amino acids be synthesized by the body? | NO!
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| When pyruvate is transaminated, what does it synthesize? | Alanine
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| When oxaloacetate is transaminated, what does it synthesize? | Aspartate
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| When alpha-ketoglutarate is transaminated, what does it synthesize? | Glutamate
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| What forms alanine by transamination? | Pyruvate
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| What forms aspartate by transamination? | Oxaloacetate
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| What forms glutamate by transamination? | alpha-ketoglutarate
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| Where is arginine generated? | Urea cycle
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| Where does Cysteine get its S? | Methionine
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| Can some enzymes used in amino acid synthesis also be used in amino acid degradation? | YES! example: transaminases
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| What is pyridoxal phosphate (PLP) synthesized from? | Vitamin B6
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| What are two mechanisms through which nitrogen is removed from amino acids? | TransaminationDeamination
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| What is deamination? | Where an amino group is removed. This results in ammonia production.
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| 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)
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| What do alpha-ketoglutarate and glutamate do in transamination? | Alpha-ketoglutarate accepts the amino acid in transamination, which causes the formation of glutamate.
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| What is another name for aminotransferases? | Transaminases
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| What is another name for transaminases? | Aminotransferases
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| What do transaminases/aminotransferases require as a cofactor? | PLP
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| Is transamination reversible? | YES!
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| Why is it important that transamination be reversible? | It enables the same enzymes to be used in amino acid degradation and amino acid synthesis.
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| The direction of a transaminase reaction will reverse in response to ... | changes in concentration.
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| What does ALT catalyze? | Pyruvate --> alanine
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| What enzyme is involved in the pyruvate --> alanine reaction? | ALT
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| What does AST catalyze? | Oxaloacetate --> aspartate
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| What enzyme is involved in the oxaloacetate --> aspartate reaction? | AST
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| 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.)
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| What is the function of glutamate dehydrogenase? | It deaminates glutamate, resulting in alpha-ketoglutarate and ammonia.
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| Where does the deamination of glutamate by glutamate dehydrogenase take place? | Liver
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| What enzyme is involved in the deamination of glutamate into alpha-ketoglutarate and ammonia? | glutamate dehydrogenase
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| What enzyme is involved in the conversion of glutamate + ammonium (NH4+) --> glutamine | Glutamine synthase
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| What conversion does glutamine synthase catalyze? | glutamate and ammonium --> glutamine
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| How many ammonia molecules does glutamine have? | two
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| What enzyme is involved in the conversion:glutamine --> glutamate + NH4+? | Glutaminase
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| What does glutaminase do? | Removes an ammonium from glutamine to create glutamate.
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| What transport role is alanine important in? | Transporting ammonia to the liver.
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| 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).
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| What defines glucogenic amino acids? | Can create glucose.Ultimately degraded to pyruvate or TCA cycle intermediates.
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| What defines ketogenic amino acids? | CANNOT make glucose.Ultimately degraded to Acetyl CoA or acetoacetate.
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| 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.
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| 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.
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| What is the effect of glucagon on amino acid metabolism? | Stimulates uptake of amino acids into the liver.
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| Do insulin, cortisol, and glucagon stimulate the uptake of amino acids into the liver? | YES!
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| 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
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| What is a hypercatabolic state? | State of increased fuel usage.Negative nitrogen balance.Cortisol is a mediator.Ex. defense against infection/wound healing
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| Where does the urea cycle occur? | Liver
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| What is the enzyme that converts HCO3- + NH4+ --> Carbamoyl phosphate? | CPS1 (carbamoyl phosphate synthase 1)
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| What is the rate limiting step in the urea cycle? | CPS1 (carbamoyl phosphate synthase 1)
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| What is the enzyme that converts Ornithine to Citrulline? | OTC (ornithine transcarbomylase)
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| Where do the two N's in urea come from? | One from ammoniaone from aspartate
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| What is the common source of both of the N's in urea? | Glutamate
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| Where do the first two steps of the urea cycle occur? | Mitochondria
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| In the urea cycle, after the first two steps, where do the following steps occur? | Cytoplasm
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| What are two products from the urea cycle? | arginine fumarate
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| Is ornithine regenerated? | YES!
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| Is the process of urea formation irreversible? | YES!
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| What is the rate limiting step of the urea cycle? | CPS1
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| How is the urea cycle regulated? | Feed forward process(substrate availability)
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| Does CPS1 have an allosteric regulator? | YES!
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| What is the role of NAG in the urea cycle? | It is synthesized by acetyl CoA and glutamate and it STIMULATES CPS1
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| 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.
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| What is BUN? | Blood Urea Nitrogen, measure of urea concentration in blood.
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| What does an elevated BUN show? | kidney failure
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| What does a low BUN show? | liver disease
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| How does diet affect BUN? | more protein in the diet will show higher BUN levels.
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| What is hyperammonemia? | Increased ammonia levels in the blood.Caused by liver disease or kidney failure (more urea metabolized by intestinal bacteria = incr. BUN)
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| Ornithine transcarbamoylase deficiency (OTC), the most common cause of urea cycle disorder, is what type of genetic trait? | x-linked.
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