29 - Amino Acid Metabolism Flashcards
These are shitty shitty notes..
is alanine essential or non-essential? Glucogenic, ketogenic or both?
Non-essential
glucogenic
Is asparagine essential or non-essential? Glucogenic, ketogenic or both?
non-essential
glucogenic
Is aspartic acid essential or non-essential? Glucogenic, ketogenic or both?
non-essential
glucogenic
Is cysteine essential or non-essential? Glucogenic, ketogenic or both?
non-essential
glucogenic
is glutamic acid essential or non-essential? Glucogenic, ketogenic or both?
non-essential
glucogenic
is glutamine essential or non-essential? Glucogenic, ketogenic or both?
non-essential
glutogenic
is glycine essential or non-essential? Glucogenic, ketogenic or both?
non-essential
glutogenic
is proline essential or non-essential? Glucogenic, ketogenic or both?
non-essential
glutogenic
is serine essential or non-essential? Glucogenic, ketogenic or both?
non-essential
glucogenic
is tyrosine essential or non-essential? Glucogenic, ketogenic or both?
non-essential
both
is ornithine/taurine essential or non-essential? Glucogenic, ketogenic or both?
non-essential
both
is arginine essential or non-essential? Glucogenic, ketogenic or both?
essential (but insufficient synthesis)
glucogenic
is histidine essential or non-essential? Glucogenic, ketogenic or both?
essential
both
is isoleucine essential or non-essential? Glucogenic, ketogenic or both?
essential
both
is leucine essential or non-essential? Glucogenic, ketogenic or both?
essential
ketogenic
is lysine essential or non-essential? Glucogenic, ketogenic or both?
essential
ketogenic
is methionine essential or non-essential? Glucogenic, ketogenic or both?
essential (but insufficient synthesis)
glucogenic
is phenylalanine essential or non-essential? Glucogenic, ketogenic or both?
essential (but insufficient synthesis)
both
is threonine essential or non-essential? Glucogenic, ketogenic or both?
essential
both
is tryptophan essential or non-essential? Glucogenic, ketogenic or both?
essential
both
is valine essential or non-essential? Glucogenic, ketogenic or both?
essential
glucogenic
Which amino acids can be broken down in the human body?
all
When amino acids are degraded, where do their components go?
The carbon skeleton is converted into energy metabolites and the amino group goes into urea (in the liver) for excretion
What are transaminases? What are transaminations?
These convert the amino group on an amino acid with a keto group on a ketoacid (like alpha-ketoglutarate)
For example, alanine and alpha-ketoglutarate can be converted to glutamate and pyruvate with transaminase.
This is a transaminatino reaction.
All transaminases have pyridoxal phosphates as a prosthetic group,
pyridoxal phosphates are derived from pyridoxine (vitamin B6)
Transaminases are also called aminotransferases.
What ensures that transaminations of aspartate/oxaloacetate continue?
Antiporters for glutamate and aspartate. This way aspartate is stuck in the cytosol to react with glutarate and form oxaloacetate (transamination) to feed into gluconeogenesis.
What is important about aspartate aminotransferase?
The transamination of alpha-ketoglutarate + aspartate to glutamate + oxaloacetate
This is a step to make oxaloacetate that will be used in gluconeogenesis. This must happen in the cytosol, because oxaloacetate can’t be transported into cytosol form mitochondria, but aspartate can.
What is the malate aspartate shuttle?
Import of NADH into mitochondria for use in oxidative phosporylation achieved by converting between aspartate/glutamate and oxaloacetate/malate (converting from malate to oxaloacetate in mitochondria generates an NADH)
What enzyme catalyzes oxidative deamination and reductive amination of glutamate/alpha-ketoglutarate in mitochondrial matrix?
glutamate dehydrogenase
Reversible reaction: direction determined by reactant concentrations (including ammonium and pH)
How is glutamine synthesized?
Glutamine acts as an amino group carrier
- Glutamine synthetase converts glutamate + ammonium to glutamine (costs ATP) which forms an amide bond
This is an irreversible reaction
What enzyme catalyzes the conversion of glutamine to glutamate?
Glutaminase
What happens to carbon skeletons from the degradation of glucogenic amino acids?
Used for pyruvate or TCA cycle intermediates
Useful for anaplerosis and gluconeogenesis
What happens to carbon skeletons form degradation of ketogenic amino acids?
Converted to acetyl-CoA (energy substrate), but not for gluconeogenesis or anaplerotic reactions
What is the transsulfuration pathway?
Breakdown of methionine. It is important for the generation of S-adenosyl methionine (SAM)
Linked to tetrahydrofolate metabolism
Methionine metabolism is connected to :one-carbon metabolism” transmethylations
What is the precursor for tetrahydrofolate (THF)?
Vitamin B9, folic acid, synthesized by microorganisms.
Synthesis from folate is catalyzed by dihydrofolate reductase
What does tetrahydrogolate (THF) do?
Transfers C1 groups in several oxidation states
Used for
- Amino acid synthesis
- Purine synthesis
- Thymidine monophosphate synthesis
What happens if there is a folate deficiency?
Unable to make THF, used in amino acid synthesis, purine synthesis and thymidine monophosphate synthesis
Results in
- Neural tube defects and anemia
Deficiency is usually due to increased demand and poor absorption or drugs that inhibit dihydrofolate reductase
What does vitamin B12 (cobalamine) do?
Can convert various amino acids (valine, isoleucine and threonine) as well as odd chain fatty acids which have been converted to methylmaalonyl-CoA to succinyl CoA
Also can convert homocysteine to methionine, homocysteine has a role in methylgroup transfer reactions.
How are branched chain amino acids broken down?
Transamination to a ketoacid and then decarboxylation with BCKD (using NAD+ and CoASH)
What does a defect in BCKD cause?
BCKD catalyzes the decarboxylation of branched chain amino acids (after they’ve been transminated)
A defect leads to maple syrup urine disease. This eventually leads to brain damage and death
What does the glucose-alanine cycle do?
Gets rid of excess nitrogen:
- Alanine is transported to the liver and transminated with alpha-ketoglutarate to glutamate and pyruvate
- Part of the glutamate is oxidatively deaminated by glutamate dehydrogenase to alpha-ketoglutarate and ammonium
- part of the glutamate is transaminated to aspartate
- aspartate and NH4 go into urea synthesis
What is the urea cycle?
Where aspartate and ammonium from the glucose-alanine cycle in converted to urea for excretion.
In terrestrial vertebrates most nitrogen must be excreted (a little is used in biosynthetic reactions)
Urea cycle is in liver
Where do the two amino groups of urea come from?
One comes from Ammonium and the other comes from aspartate
What are the steps of the urea cycle?
- Synthesis of carbamoyl phosphate
- Entry into cycle:transer of carbamoyl group to ornithine
- Second aminogroup from aspartate
- Fumarate formation
- Formation of urea, regeneration of ornithine
The urea cycle is linked to what other cycle and how?
The urea cycle is linked to the citric acid cycle. Fumarate made in the urea cycle enters the citric acid cycle and is converted to oxaloacetate needed for transamination.
What is usually happening when there is a negative nitrogen balance (more nitrogen going out than in)?
- Starvation
- Serious illness
- Insufficient essential amino acids
What is usually happening when there is a positive nitrogen balance (more nitrogen going in than out)?
- Growth
- Pregnancy
- Recovery from illness or starvation
What can alpha-keto acids from transamination of amino acids (in their degradation) be precursors for?
CO2 and H2O
GLucose
Ketones and fatty acids
