Amino Acid Degredation

Why must proteins in organisms be continually degraded?

To remove damaged/misfolded proteins, regulate enzyme levels, and provide amino acids for new proteins and energy metabolism

What chemical element separates amino acids from carbohydrates and lipids?

Nitrogen

What functional group is unique to amino acids?

Amino group (-NH₂)

What are the two main uses for free amino acids in the body?

1) Protein synthesis, 2) Catabolism for energy and metabolite production

Name one physiological effect of hyperammonemia.

Neurological toxicity due to increased brain glutamine

Name another effect of hyperammonemia.

Cerebral edema

Name another effect of hyperammonemia 3

Lethargy or coma

Another effect of hyperammonemia 4?

Disruption of neurotransmitter balance

Fifth effect of hyperammonemia?

Interference with TCA cycle intermediates → energy deficiency

Name three common mechanisms for removing amino groups.

Transamination, oxidative deamination, direct release as ammonia

What is the general reaction catalyzed by aminotransferases?

Amino acid + α-keto acid ↔ new amino acid + new α-keto acid

What typically serves as the amino group acceptor in transamination?

α-Ketoglutarate

Example: transamination of alanine + α-ketoglutarate yields what products?

Pyruvate + glutamate

What is the purpose of the glucose-alanine cycle?

Transport amino groups from muscle to liver while recycling carbon skeletons for glucose production

How is the glucose-alanine cycle similar to the Cori cycle?

Both transport metabolites from muscle to liver and return energy substrates

How does the glucose-alanine cycle differ from the Cori cycle?

Transfers nitrogen (glucose-alanine) vs lactate (Cori)

What reaction does glutamate dehydrogenase catalyze?

Glutamate + NAD(P)⁺ + H₂O → α-ketoglutarate + NH₄⁺ + NAD(P)H

Where does the urea cycle occur?

Mitochondria and cytosol of liver cells

What is the first metabolite in the urea cycle?

Carbamoyl phosphate

Name the main intermediates of the urea cycle.

Ornithine, citrulline, argininosuccinate, arginine, urea

Which enzymes are key in the urea cycle?

Carbamoyl phosphate synthetase I, ornithine transcarbamylase, argininosuccinate synthetase, argininosuccinate lyase, arginase

Where is ATP consumed in the urea cycle?

1) Formation of carbamoyl phosphate (2 ATP), 2) Formation of argininosuccinate (1 ATP → AMP equivalent)

What is the total energy cost to make one urea molecule?

4 high-energy phosphate bonds (3 ATP equivalents)

How is the urea cycle integrated with the TCA cycle?

Fumarate from argininosuccinate → TCA cycle intermediates → gluconeogenesis

What is the structural difference between keto and amino acids?

Amino acids have -NH₂ at α-carbon; keto acids have =O at α-carbon

Pair alanine, aspartate, glutamate with their keto acids.

Alanine ↔ pyruvate, Aspartate ↔ oxaloacetate, Glutamate ↔ α-ketoglutarate

What changes at the α-carbon in transamination?

Amino group transferred to keto acid, α-hydrogen replaced by keto group

Name five amino acids that enter TCA cycle via simple degradation pathways.

Glutamate → α-ketoglutarate, Aspartate → oxaloacetate, Alanine → pyruvate, Valine/Isoleucine → succinyl-CoA, Phenylalanine/Tyrosine → fumarate/acetoacetate

What is the difference between glucogenic and ketogenic amino acids?

Glucogenic → converted to glucose precursors; Ketogenic → converted to acetyl-CoA or acetoacetate

Name exclusively ketogenic amino acids.

Leucine and lysine

Name glucogenic amino acids.

Most others (e.g., alanine, glutamate, aspartate)

Name amino acids that are both glucogenic and ketogenic.

Isoleucine, phenylalanine, tyrosine, tryptophan, threonine

What are the seven common metabolites from amino acid degradation?

Pyruvate, α-ketoglutarate, succinyl-CoA, fumarate, oxaloacetate, acetyl-CoA, acetoacetate

Which of the seven metabolites are glucogenic?

Pyruvate, α-ketoglutarate, succinyl-CoA, fumarate, oxaloacetate

Which are ketogenic?

Acetyl-CoA, acetoacetate

Why can exclusively ketogenic amino acids not form glucose?

Acetyl-CoA and acetoacetate cannot be converted to net glucose in mammals