BCII: Fate of Amino Acids

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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.

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

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