How does the concept of a circle relate to cyclins?

The detail answer is given in the explanation section.

Explanation:

Cyclins are among the most essential core cell cycle regulators. Cyclins are a group of related proteins.  There are four basic types found in humans and most other eukaryotes. Each cyclin is correlated with a particular condition, transition, or set of stages in the cell cycle, and thus, they help to make the events of that phase or period.

A typical cyclin is present at the lower levels for most of the cycle but increases sharply at the stage where it's required.

the tricuspid valve is present between right atrium and right ventricle

paper covers rock.

explanation:

rock only smashes scissors.