Quiz on Protein Metabolism

What are the two sources of proteins subjected to digestion and absorption?

• Complete and Incomplete

• Animal and Plant

• Essential and Non-essential

• Exogenous and Endogenous

Answer explanation

Proteins are sourced from two main categories: exogenous (from food) and endogenous (produced by the body). The correct answer highlights these two sources, distinguishing them from other classifications like animal/plant or essential/non-essential.

What is the primary function of the liver in amino acid metabolism?

• Digest dietary proteins

• Synthesize new proteins

• Store amino acids

• Absorb nutrients

Answer explanation

The primary function of the liver in amino acid metabolism is to synthesize new proteins. It converts amino acids into proteins needed for various bodily functions, making this the correct choice.

What is the first step in amino acid degradation?

• Gluconeogenesis

• Transamination

• Deamination

• Ketogenesis

Answer explanation

The first step in amino acid degradation is deamination, which involves the removal of the amino group from the amino acid, converting it into a corresponding keto acid and ammonia.

Which amino acids are converted to glucose through gluconeogenesis?

• Non-essential amino acids

• Essential amino acids

• Ketogenic amino acids

• Glucogenic amino acids

Answer explanation

Glucogenic amino acids can be converted into glucose through gluconeogenesis. Unlike ketogenic amino acids, which are converted to ketone bodies, glucogenic amino acids contribute to glucose production.

What is the role of glutamate dehydrogenase?

• Store nitrogen

• Synthesize proteins

• Catalyze oxidative deamination

• Transport amino acids

Answer explanation

Glutamate dehydrogenase catalyzes oxidative deamination, a process that converts glutamate to alpha-ketoglutarate while releasing ammonia. This is crucial for amino acid metabolism and nitrogen balance.

Alanine is transaminated to

• pyruvate

• α-ketoglutarate

• oxaloacetate

• fumarate

Answer explanation

Alanine is transaminated to pyruvate through the action of the enzyme alanine transaminase. This process involves the transfer of an amino group from alanine to α-ketoglutarate, forming pyruvate and glutamate.

What is produced by the oxidative deamination of amino acids?

• Urea

• Free ammonium ion

• Fatty acids

• Glucose

Answer explanation

The oxidative deamination of amino acids primarily produces free ammonium ions, which can be further processed in the urea cycle. Urea is a product of this cycle, but the immediate product of deamination is the ammonium ion.

What connects the Krebs cycle to the urea cycle?

• α-ketoglutarate

• Glutamate

• Alanine

• Aspartate

Answer explanation

Aspartate connects the Krebs cycle to the urea cycle as it is formed from oxaloacetate in the Krebs cycle and is a key substrate in the urea cycle, participating in the transamination and nitrogen disposal processes.

What is the fate of nitrogen derived from muscle protein breakdown?

• Stored as fat

• Excreted as urea

• Used for energy

• Converted to alanine

Answer explanation

Nitrogen from muscle protein breakdown is primarily converted to alanine, which can be used in gluconeogenesis or as a transport form of nitrogen. This process helps in maintaining nitrogen balance in the body.

What is the main transporter of ammonia in the blood?

• Alanine and glutamine

• Glutamate and aspartate

• Lysine and threonine

• Serine and proline