Question

Explain the purpose of a molecular clock and the properties that a section of protein must have to be used in this way.

Answer 1

The term "molecular clock" is actually too vague to answer.

It could refer to comparing differences in DNA and amino acid sequence of individual genes and proteins to measure how long ago related species diverge from one another. Or it could refer to actual molecular feedback loops (involving interacting proteins and gene regulatory networks) which measure out circadian and longer term time keeping processes in individual organisms.

If you specify which you mean, I'd be happy to answer this question. It's a good one and I'm a little sorry no one else stepped up to the plate.