Question

Describe the reactions that you would expect these enzymes to catalyze. (a) Alcohol dehydrogenase (b) Aspartate transaminase (c) Tyrosine-tRNA synthetase (d) Phosphohexose isomerase

Short answer

(a) Oxidizes alcohols; (b) Transfers amino groups; (c) Attaches tyrosine to tRNA; (d) Isomerizes hexose phosphates.

Step-by-step solution

Understand the Role of Alcohol Dehydrogenase

Alcohol dehydrogenase is an enzyme that primarily catalyzes the oxidation of alcohols to aldehydes or ketones. This reaction involves the removal of hydrogen atoms from the alcohol, using a coenzyme such as NAD+ or NADP+ as an electron acceptor. For example, ethanol is converted to acetaldehyde in the liver during alcohol metabolism.

Explore Aspartate Transaminase Function

Aspartate transaminase is an enzyme that catalyzes the transfer of an amino group from aspartate to alpha-ketoglutarate, forming oxaloacetate and glutamate. This transamination reaction is part of the amino acid metabolism and plays a critical role in the urea cycle and gluconeogenesis.

Examine the Role of Tyrosine-tRNA Synthetase

Tyrosine-tRNA synthetase is responsible for attaching the amino acid tyrosine to its corresponding tRNA molecule. This process, known as aminoacylation, involves the activation of tyrosine with ATP to form a tyrosyl-AMP intermediate, which then transfers the tyrosine to the tRNA. This step is essential for protein synthesis during translation.

Analyze the Function of Phosphohexose Isomerase

Phosphohexose isomerase, also known as glucose-6-phosphate isomerase, catalyzes the isomerization of glucose-6-phosphate to fructose-6-phosphate. This reversible reaction forms part of the glycolytic and gluconeogenesis pathways, facilitating the metabolism of carbohydrates.

Key concepts

Alcohol Dehydrogenase

The enzyme Alcohol Dehydrogenase plays a crucial role in metabolizing alcohol within the body. It is primarily responsible for the oxidation of alcohols to aldehydes or ketones. This transformation is an essential part of breaking down alcoholic beverages in the body. The reaction involves removing hydrogen atoms from the alcohol molecule. The enzyme uses coenzymes like NAD+ or NADP+ to help transfer these electrons. This process transforms ethanol into acetaldehyde, which occurs mainly in the liver. The ability to catalyze this reaction effectively is why Alcohol Dehydrogenase is pivotal in alcohol metabolism and detoxification.

Aspartate Transaminase

Aspartate Transaminase is an important enzyme involved in amino acid metabolism. It catalyzes the transfer of an amino group from aspartate to alpha-ketoglutarate. This reaction results in the formation of oxaloacetate and glutamate.
This transamination process is essential for the body's urea cycle and gluconeogenesis—essential processes for managing waste and producing glucose.

• This enzyme helps maintain a balance of amino acids.
• It is also vital for detoxifying excess nitrogen from the body.

The effective function of Aspartate Transaminase is crucial for converting nutrients into energy and for the proper functioning of cellular metabolism.

Tyrosine-tRNA Synthetase

Tyrosine-tRNA Synthetase is a key enzyme in genetic translation. It aids in attaching the amino acid tyrosine to its corresponding tRNA molecule. This process, called aminoacylation, is crucial for effective protein synthesis. The enzyme first activates tyrosine using ATP to form a complex known as tyrosyl-AMP. This intermediate then transfers the tyrosine to a tRNA specifically designed for tyrosine. This step ensures that proteins are built accurately, with tyrosine being one of the building blocks required for the growing polypeptide chain.

Phosphohexose Isomerase

Phosphohexose Isomerase, also called glucose-6-phosphate isomerase, is an enzyme involved in carbohydrate metabolism. It catalyzes the reversible conversion of glucose-6-phosphate to fructose-6-phosphate. This reaction is a key step in both the glycolytic pathway (glycolysis) and gluconeogenesis.

• It allows the continuation of glycolysis, which is the process of breaking down glucose to generate energy.
• It also plays a role in gluconeogenesis, which is the process of generating glucose from non-carbohydrate sources.

The reversible nature of this reaction demonstrates the enzyme's flexibility in adapting to the body's energy needs.