STEM - Free Printable

Let’s go step by step through each labeled stage in the diagram to understand what’s happening during cell signaling that leads to mitosis.

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Stage ①: Growth factor binds to receptor

- A growth factor (the pink circle) floats outside the cell and attaches to a specific receptor on the cell membrane.
- This is like a key fitting into a lock — only the right growth factor can bind to its matching receptor.
- When it binds, it “turns on” the receptor so it can send signals inside the cell.

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Stage ②: Adenylate cyclase makes cAMP

- The activated receptor turns on an enzyme called adenylate cyclase (shown as red blocks in the membrane).
- Adenylate cyclase takes ATP (energy molecules shown as red circles + green shapes) and converts them into cAMP (cyclic AMP — shown as one red circle + two green shapes).
- cAMP acts as a second messenger — it carries the signal from the membrane deeper into the cell.

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Stage ③: Kinase gets switched ON

- cAMP activates a kinase protein (originally OFF, gray shape).
- Once activated, the kinase changes shape and becomes active (now purple, labeled “Kinase ON”).
- Kinases are enzymes that add phosphate groups to other proteins to turn them on or off — here, it’s turning on the next part of the chain.

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Stage ④: Gene transcription starts

- The activated kinase (now called Kinase 2, green shape) moves to the DNA in the nucleus.
- It helps start the process of reading a gene — this is called transcription.
- The DNA double helix opens up, and RNA polymerase (not shown but implied) reads the DNA code to make a strand of RNA (shown as the ladder-like structure below DNA).

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Stage ⑤: Protein made from RNA

- The RNA molecule leaves the nucleus and goes to a ribosome (not shown, but where protein synthesis happens).
- The ribosome reads the RNA and builds a new protein (shown as the yellow circle).
- This protein is likely involved in controlling the cell cycle — maybe a cyclin or something similar.

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Stage ⑥: Cell enters cell cycle → Mitosis

- The newly made protein pushes the cell into the cell cycle (red circular arrow labeled “Cell cycle”).
- As the cell progresses through the cycle, it prepares to divide.
- Finally, the cell undergoes mitosis — splitting into two identical daughter cells (shown at bottom left).

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Final Answer:

① Growth factor binds to receptor on cell surface, activating it.
② Activated receptor triggers adenylate cyclase to convert ATP into cAMP.
③ cAMP activates a kinase (changes it from OFF to ON).
④ Activated kinase helps start transcription — DNA is copied into RNA.
⑤ RNA is used to build a new protein that controls the cell cycle.
⑥ That protein causes the cell to enter the cell cycle and eventually divide via mitosis.