just wanted to add that questions that ask small details like this make me want to carve my eyeballs out

Another way to think about this is whats the closes stage to mitosis because right before M (mitosis) you need to have mitotic cyclins synthesized, and that would be G2

G1 --> S --> G2 --> M

Cyclin A,D,E and for G1 to S transition [made in G1]. Cyclin B is for G2 to M transition[made in G2].

G1 checkpoint: Cyclin D/CDK4 complex with p53 and rb G2 checkpoint: Cyclin B and CDK 1

Way to remember: G1 is associated with higher numbers D and 4 G2 is associated with B and 1

Amboss

and also F@CK me and F@CK NBME!!!

Main groups There are two main groups of cyclins:

• G1/S cyclins – essential for the control of the cell cycle at the G1/S transition;
• Cyclin A / CDK2 – active in S phase.
• Cyclin D / CDK4, Cyclin D / CDK6, and Cyclin E / CDK2 – regulates transition from G1 to S phase.
• G2/M cyclins – essential for the control of the cell cycle at the G2/M transition (mitosis). G2/M cyclins accumulate steadily during G2 and are abruptly destroyed as cells exit from mitosis (at the end of the M-phase).
• Cyclin B / CDK1 – regulates progression from G2 to M phase.

Amboss for cyclin：

G2 checkpoint: A cell division checkpoint during the G2 phase.
Checks for DNA damage and completeness of DNA replication
Initiates mitosis by phosphorylation of various proteins (e.g., histones)
Regulated by the mitosis promoting factor (MPF), which is composed of Cdk1 and cyclin B.