Which enzyme class catalyzes the joining of two substrate molecules?

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Multiple Choice

Which enzyme class catalyzes the joining of two substrate molecules?

Ligases catalyze the joining of two substrate molecules to form a single new product, typically by creating a covalent bond and often using energy from ATP to drive the condensation reaction. This is exactly the action needed when two separate molecules are fused together, such as DNA ligase sealing fragments of DNA by forming phosphodiester bonds. Other enzyme classes focus on different activities: hydrolases cleave bonds by adding water, isomerases rearrange atoms within a single molecule, and lyases cleave or rearrange bonds without hydrolysis, often forming or removing double bonds rather than linking two substrates. Because the question asks which class is specialized for joining substrates, ligases are the best answer.

Ligases catalyze the joining of two substrate molecules to form a single new product, typically by creating a covalent bond and often using energy from ATP to drive the condensation reaction. This is exactly the action needed when two separate molecules are fused together, such as DNA ligase sealing fragments of DNA by forming phosphodiester bonds. Other enzyme classes focus on different activities: hydrolases cleave bonds by adding water, isomerases rearrange atoms within a single molecule, and lyases cleave or rearrange bonds without hydrolysis, often forming or removing double bonds rather than linking two substrates. Because the question asks which class is specialized for joining substrates, ligases are the best answer.

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