Read the below statements about enzymes and choose the correct option: 1. Enzymes increase the activation energy of a reaction. 2. Enzymes are specific to substrates due to active site configuration. 3. Enzyme activity is affected by pH and temperature. Which of the above statements are correct?

Correct — B. Judge each statement on its own.

Statement 1 is false. Enzymes lower the activation energy, the energy barrier a reaction has to cross. That is how they speed reactions up.

Statement 2 is true. The substrate fits into the active site, a pocket in the enzyme, and that fit decides which substrate the enzyme acts on.

Statement 3 is true. Each enzyme works best at an optimum temperature and pH, and its activity falls on either side.

Statements 2 and 3 → option (b).

Why the others are wrong

• (a)
  Only 1 and 2 are correct — Statement 1 is false. Enzymes lower the activation energy, they do not raise it. This option also leaves out statement 3, which is true.
• (c)
  Only 1 and 3 are correct — Statement 1 is the wrong one to keep. A catalyst that raised the energy barrier would slow a reaction down. This option also drops statement 2 on the active site, which is true.
• (d)
  1, 2 and 3 all are correct — Statement 1 sinks it. Enzymes speed reactions up by lowering the activation energy, so any set that includes statement 1 is wrong.

Enzymes are biological catalysts. NCERT notes that almost all enzymes are proteins. The exceptions are ribozymes, nucleic acids that behave like enzymes.

A reacting substrate must pass through a high-energy transition state. The energy gap between the substrate and that state is the activation energy. An enzyme brings this barrier down, so the reaction runs faster, and the enzyme comes out unchanged.

The substrate binds in the active site, a crevice or pocket in the folded protein.

Key facts

• Enzymes lower the activation energy of a reaction and come out of it unchanged.
• The active site is the pocket or crevice in an enzyme into which the substrate fits.
• Each enzyme has an optimum temperature and an optimum pH, and its activity declines on either side of them.
• Ribozymes are nucleic acids with catalytic power, so not every biological catalyst is a protein.

Common traps

• Reading 'catalyst' as 'supplies energy': an enzyme lowers the energy barrier, it does not add the energy to climb it.
• Assuming cold denatures an enzyme the way heat does: low temperature only keeps it temporarily inactive.

No directly related past PYQ was found.