Cell cycle regulation exercise - Free Printable

Let’s solve this step by step.

We are working with the cell cycle checkpoints — these are like “traffic lights” that make sure everything is ready before the cell moves to the next stage. There are four main checkpoints: G1, S, G2, and M.

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Part 1: Drag labels to correct stages (diagram)

Even though we can’t drag, we can match them logically based on where they occur in the cell cycle:

The cell cycle goes:
G1 → S → G2 → M → back to G1

Checkpoints happen at key transitions:

- G1 checkpoint → right after G1, before entering S phase. Checks if conditions are good for DNA replication.
- S checkpoint → during S phase. Monitors DNA replication as it happens.
- G2 checkpoint → after S phase, before M phase. Checks if DNA was copied correctly and no damage.
- M checkpoint → during mitosis (metaphase). Checks if chromosomes are properly attached to spindle fibers.

Looking at the diagram (even without seeing colors), the traffic lights are placed at transition points between phases. The blue boxes likely represent the phases themselves, and the traffic lights are the checkpoints.

But since the question asks to drag labels to stages, and we have 4 checkpoint names and 4 traffic light positions, we assign:

→ Top-left traffic light (before green segment): G1 checkpoint
→ Top-right traffic light (after purple/blue segment labeled “C”): M checkpoint
→ Bottom-right traffic light (after yellow segment): G2 checkpoint
→ Bottom-left traffic light (after red segment): S checkpoint

Wait — let’s think again using standard order.

Standard cell cycle flow clockwise:

Start at top: usually G1 → then S → then G2 → then M → back to G1.

In many diagrams:

- Yellow arc = G1
- Green arc = S
- Red arc = G2
- Purple/blue arc = M

Traffic lights are at the *end* of each phase, checking before moving to next.

So:

- After G1 (yellow) → before S → G1 checkpoint
- During S (green) → S checkpoint (sometimes shown mid-phase)
- After G2 (red) → before M → G2 checkpoint
- During M (purple) → specifically at metaphase → M checkpoint

Given the traffic light positions:

Assume clockwise from top:

Top traffic light → end of G1 → G1 checkpoint
Right traffic light → during M → M checkpoint
Bottom traffic light → end of G2 → G2 checkpoint
Left traffic light → during S → S checkpoint

That matches standard teaching diagrams.

So labeling the traffic lights (from top, going clockwise):

1. Top → G1 checkpoint
2. Right → M checkpoint
3. Bottom → G2 checkpoint
4. Left → S checkpoint

But wait — the practice section gives us clues too.

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Part 2: Practice sentences

We need to fill in:

1. During ______, the attachment of sister chromatids to spindle fibers is checked.
→ That’s the M checkpoint (happens in metaphase of mitosis).

2. During ______, the possibility of DNA damage is checked.
→ This could be G1 or G2. But G2 checks for DNA damage *after* replication. G1 checks before replication. Since sentence doesn’t specify, but often “DNA damage” check is emphasized at G2. However, looking at options: we have “G₂ stage checkpoint”, “S stage checkpoint”, etc.

Actually, both G1 and G2 check for DNA damage. But in context of the options given, and typical textbook focus:

Sentence 2: “During ______, the possibility of DNA damage is checked.” → Most commonly associated with G2 checkpoint, because it checks if DNA was damaged *during* S phase.

But let’s see sentence 3:

3. During the S phase checkpoint, any ______ problem is monitored.
→ Obviously, DNA replication problems.

Now look at available terms to drop:

Options:
- G₂ stage checkpoint
- C stage checkpoint ← probably typo? Should be “M”? Or maybe “C” for cytokinesis? Not standard. Probably ignore or assume error.
- S stage checkpoint
- M stage checkpoint
- DNA replication

So for sentence 1: “attachment of sister chromatids to spindle fibers” → M stage checkpoint

Sentence 2: “possibility of DNA damage is checked” → best fit is G₂ stage checkpoint (since it checks after DNA synthesis)

Sentence 3: “During the S phase checkpoint, any ______ problem” → DNA replication

Note: “C stage checkpoint” is not a real term — likely distractor or typo. We won’t use it.

Also, note: sometimes “S checkpoint” monitors replication errors, which ties to sentence 3.

So final matching for practice:

1. M stage checkpoint
2. G₂ stage checkpoint
3. DNA replication

This also helps confirm our earlier diagram logic.

Back to diagram: if we know M checkpoint is when chromatid-spindle attachment is checked, and that happens during M phase, so the traffic light during M phase should be labeled M checkpoint.

Similarly, G2 checkpoint is after S, before M — so bottom traffic light (if yellow=G1, green=S, red=G2, purple=M) then after red (G2) comes M, so traffic light at end of red = G2 checkpoint.

Left traffic light (during green/S phase) = S checkpoint.

Top traffic light (end of yellow/G1) = G1 checkpoint.

Perfect.

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Final Answers:

For the diagram (dragging labels to traffic lights, assuming clockwise from top):

- Top traffic light → G1 checkpoint
- Right traffic light → M checkpoint
- Bottom traffic light → G2 checkpoint
- Left traffic light → S checkpoint

For the practice sentences:

1. During M stage checkpoint, the attachment of sister chromatids to spindle fibers is checked.
2. During G₂ stage checkpoint, the possibility of DNA damage is checked.
3. During the S phase checkpoint, any DNA replication problem is monitored.

(Note: “C stage checkpoint” is not used — likely incorrect option.)

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Final Answer:
Diagram labels (clockwise from top): G1 checkpoint, M checkpoint, G2 checkpoint, S checkpoint
Practice sentences:
1. M stage checkpoint
2. G₂ stage checkpoint
3. DNA replication