Question

Arrange the steps of light-dependent (photoreactivation) repair in the correct order:

a) uv irradiation creates a thymine dimer.
b) the enzyme photolyase binds to the thymine dimer.
c) the cross-links between the thymine dimer are cleaved, and photolyase is released.
d) photolyase is activated by the absorption of blue light.
Choose the correct order:
a, b, c, d
a, c, b, d
c, b, a, d
d, b, c, a
d, a, b, c

Answer 1

The correct order for light-dependent (photoreactivation) repair is: UV irradiation creates a thymine dimer, photolyase binds to the dimer, activation by blue light, and cleavage of the dimer and release of photolyase.

Step-by-step explanation:

The correct order of steps for light-dependent (photoreactivation) repair after UV irradiation creating a thymine dimer is as follows:

1. UV irradiation creates a thymine dimer.
2. The enzyme photolyase binds to the thymine dimer.
3. Photolyase is activated by the absorption of blue light.
4. The cross-links between the thymine dimer are cleaved, and photolyase is released.

This sequence follows the process by which DNA repair occurs in cells after damage induced by UV light, with the specific mechanism involving the direct reversal by the enzyme photolyase, which uses the energy from blue light to repair the damage.