Blank Cell Cycle Diagram With Checkpoints

All 13 parts on the diagram

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The three checkpoints 7

G1 checkpoint It comes before S phase. A cell with damaged DNA is held here until the damage is repaired.
G2 checkpoint It comes before M phase. The cell waits until its DNA is copied in full and undamaged.
M checkpoint (spindle checkpoint) It holds the cell in metaphase. Anaphase waits until every chromosome is attached to the spindle.
G0 phase A cell here has left the cycle. It left from G1 and is not dividing.
DNA damage The G1 and G2 checkpoints both look for it. The cycle stops while it is repaired.
Fully copied DNA The G2 checkpoint also checks that copying is complete. Unfinished copying holds the cell before mitosis.
Spindle attachment Spindle fibers must hold every chromosome from both sides. The M checkpoint waits for that.

Cyclin and Cdk 6

Cyclin A protein whose level rises and falls with the cycle. It switches on a Cdk by binding to it.
Cyclin-dependent kinase (Cdk) An enzyme that works only with a cyclin bound. It adds phosphate groups to other proteins.
Cyclin-Cdk complex (MPF) The cyclin and the Cdk joined: the active form. The one that starts mitosis is called MPF.
Cyclin level rising The mitotic cyclin builds up during G2. The cell makes more and more of it.
Cyclin peak The mitotic cyclin is highest in M phase. The active complex takes the cell into mitosis.
Cyclin broken down The cyclin is destroyed as mitosis ends. Without it the Cdk is switched off.

How this list was compiled: Every name checked on 2026-10-01 against Kimball's Biology Pages: The Cell Cycle; Wikipedia: Cell cycle checkpoint, Cyclin and Maturation promoting factor, text only; and Nature Education, Scitable: CDK. Licence: own work

The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work

How it works

This is a cell cycle diagram with checkpoints, blank. The letters G1, S, G2 and M stay on the wheel so you can find your way. Thirteen names are left off, and six of them have a line drawn ready.

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The wheel: three gates, three frames, one cell

Each thick bar across the wheel is a checkpoint, named for where it stands: the G1 checkpoint between G1 and S, the G2 checkpoint between G2 and M, the M checkpoint inside M. A dotted line joins each bar to a frame showing what it checks: a broken ladder is DNA damage, two whole ladders fully copied DNA, a chromosome held from both sides spindle attachment. The lone cell at the end of the dashed arrow is in G0.

The lower chart: cyclin and its kinase

The small wedge is cyclin, the shape with a hollow the cyclin-dependent kinase, Cdk, and the two joined the cyclin-Cdk complex, MPF. The curve takes three names: cyclin level rising, cyclin peak, cyclin broken down.

The arrow inside the wheel runs clockwise: M, G1, S, G2.
A course may write G2/M checkpoint for the G2 checkpoint. It is the same gate.
The curve runs through two cycles, so the drop at the end of M and the next climb both show.

Questions and answers

Which checkpoint is the restriction point?

The G1 checkpoint. In mammalian cells it is called the restriction point; in yeast, the start point. It is where a cell becomes committed to entering the cycle; before it, a cell can delay in G1 or leave for G0.

Why is the protein called cyclin?

Because its amount in a cell rises and falls with each turn of the cycle. The curve on the sheet is that pattern for the mitotic cyclin: low through G1 and S, a climb through G2, a peak in M, then a steep drop.

What breaks down cyclin at the end of mitosis?

The anaphase-promoting complex, APC for short. It marks the mitotic cyclin for destruction, and with its cyclin gone MPF comes apart. The APC is held back until the spindle checkpoint is passed. It is not one of the thirteen names on the sheet.

Does the blank diagram have an answer key?

Yes. The key is the same two charts with all thirteen names written in. On it the M checkpoint also carries its other name, the spindle checkpoint.