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BCII: Fate of Amino Acids

Parker University - Tri 2 I make no claim to the accuracy of the content provided in this flashcard. Some of the information may not be correct.
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How are carbohydrates and fats stored in our body?
Carbohydrates stored as Glucogen

Fats are stored as Triacylglycerol
What is the metobolic fate of amino acids?
Use it or convert it to urea and eliminate it.

If it is stored, it becomes a toxic storage form.
Amino acids are broken down using what process?
By oxidative degradation (AKA deamination)
What is released after oxidative degradation?
Releases toxic ammonia (NH₄⁺)
Which conditions influence oxidative degradation of amino acids?
Accumulation of amino acids
What is the excretory form of nitrogen?
Urea
What is the source of the first nitrogen in urea?
Ammonia ion (NH₄⁺)
What is the source of the second nitrogen in urea?
Aspartic acid
Where is urea synthesized?
Urea is synthesized in the liver
What is the name of the enzymes that process the urea in the liver?
Glutamate Dehydrogenase

Urea is synthesized in the liver by the enzymes of the UREA CYCLE
What is the overall fate of amino acids?
Notice the link between the urea cycle and citric acid cycle.

In order to have a constant development of ATP, all the intermediates of the citric acid cycle need to be maintained.
What is the fate of the nitrogen skeleton of an amino acid when it is degraded oxidatively?
Metabolized and used in the citric acid cycle to synthesize glucose
What intermediate of the urea cycle is produced as a byproduct that can be supplied to the citric acid cycle?
Fumaric acid (Fumarate) - This will help fill any gaps in the citric acid cycle.
What is the name of the shunt pathway that links the urea cycle to the citric acid cycle?
The Asparatate-arginino-succinate shunt
Describe transamination reaction. Give an example including the enzyme catalyzing the reaction and the cofactor used.
Enzyme: Aminotransferase

Requires pyridoxal phosphate (Vitamin B6) as cofactor
α-Amino groups are converted to NH4+ ion by which process and enzyme?
Oxidative Deamination of Glutamate - Removal of amine group

Glutamate dehydrogenase - An oxidizing enzyme.
What type of enzyme is needed for oxidation?
dehydrogenase
What oxidizing agent is needed for Oxidative Deamination?
NAD⁺ or NADP⁺
Where is glutamate produced?
In the mitochondrial membrane and cannot cross the membrane
How is the ammonia group transported in the bloodstream?
Ammonia is Transported in the Bloodstream Safely as Glutamine and Alanine as its carriers and then finally into the Liver
What are the two enzymes needed to synthesize and break down glutamine?
Glutamine synthetase - two steps to form Glutamine from Glutamate.

Glutaminase - Converts Glutamine back to Glutamate
Where does glutaminase enzyme react?
Inside the matrix of the mitochondria.
Which α-keto acid makes alanine?
Pyruvate
What enzyme converts Pyruvate to Alanine?
Alanine aminotransferase - This happens in the live tissue
What are Alanine an Glutamine converted to once they arrive into the liver?
Back to Glutamate

Alanine uses Glutamate Pyruvate Transaminase Enzyme

Glutamine uses Glutaminase Enzyme
What happens to toxic NH₄⁺?
It is converted to less toxic urea
NH₄⁺ is converted to Carbamoyl phosphate in Mitochondria by what enzyme?
Carbamoyl phosphate synthetase I - Rate Limiting Step

CPS I for Urea Biosyntheses
What is the carrier for all the NH₄⁺?
Glutamate
Which two amino acids are the carriers of amino acid nitrogen from the muscle and other tissues to the liver?
Alanine an Glutamine
Which enzyme is involved for the conversion of glutamate to alanine?
alanine aminotransferase
Which compound is required to produce alanine from glutamate in the glucose-alanine cycle?
Pyruvate
Why it is necessary to convert glutamate to alanine and glutamine?
Because glutamate cannot cross the membrane; therefore, glutamate is converted to alanine and glutamine because they can cross the membrane.
Which enzyme is required to regenerate glutamate from alanine in liver tissue?
Alanine aminotransferase
Which enzyme is required to generate glutamate from glutamine in liver tissue?
Gltaminase
What is the rate-limiting step of urea biosynthesis?
Carbamoyl phosphate synthetase I
At which cellular site the rate-limiting enzyme of the urea cycle is localized?
Mitrochondria - Carbamoyl phosphate synthetase I
How is Carbamoyl phosphate synthetase I (CPS-I) regulated?
CPS-I is activated by N-Acetyl Glutamate (NAG) .

CPS-I is a Allosteric actitvator.

Arginine stimulates NAG synthesis
How bicarbonate used to form carbamoyl phosphate is activated in urea cycle reaction?
ATP - it activates the bicarbonate in the first step.
What happens during the second reaction in the first nitrogen-acquiring reaction?
Carbamate is formed by ammonia displacing phosphorly group.
What happens during the third reaction in the first nitrogen-acquiring reaction?
Carbamate is phsophorylated to to yield carbamoyl phosphate
Which intermediate is produced when ATP and bicarbonate react before ammonium ion is captured in the first reaction of urea cycle?
Carbamoyl Phosphate
How many molecules of ATPs are required to produce carbamoyl phosphate in the first priming reaction of urea cycle?
2 ATP
Nitrogen from Carbamoyl Phosphate Enters the Urea Cycle via formation of what amino acid?
Citrulline
What amino acid is used as a substrate to form Citrulline?
Ornithine - Carbamoyl Phosphate is also a substrate
How is Citrulline transfered from the mitochondria to cytosol?
Citrulline Transporter Protein
Once in the cytosol, what is the second nitrogen-acquiring reaction?
Argininosuccinate synthetase condenses citrulline with aspatate
What enyzme is responsible for producing a arginine?
Argininosuccinase
What enzyme releases urea?
Arginase catayzes the hydrolysis of arginine to produce Urea and regenerate ornithine in cytosol.
What is a byproduct in the urea cycle?
Fummarate which is fed back into the citric acid cycle.
What links the urea cycle and citric acid cycle?
Aspartate -Arginosuccinate Shunt

Fummarate which is fed back into the citric acid cycle. This links the citric acid cycle with the urea cycle.
Review the whole cycle to create Urea from Amino Acids.
How is the urea cycle regulated in regards to Substrate availability?
High rate of NH3 production, high rate of urea production
What will a High protein diet and Starvation do to the urea cycle enzymes?
Induction/repression of the synthesis of urea cycle enzymes