What you'll learn
How cells communicate and how they divide and regulate that division (~10–15% of the exam).
Cell signaling
Three stages: reception (signal binds a receptor), transduction (a relay/cascade of molecules, often amplifying), response (a cellular change). Signaling can be local (paracrine, synaptic) or long-distance (hormones/endocrine).
Feedback
- Negative feedback returns a system to set point (most homeostasis).
- Positive feedback amplifies a change (e.g. childbirth).
The cell cycle
Interphase (G1 → S, DNA replication → G2) then the mitotic phase (mitosis + cytokinesis). Mitosis stages: prophase, metaphase, anaphase, telophase → two identical diploid cells.
Regulation
Checkpoints (G1, G2, M) ensure conditions/DNA are correct before proceeding; cyclins and Cdks drive transitions. Loss of cell-cycle control → uncontrolled division (cancer).
Exam tips
- Explain how signal transduction amplifies a response.
- Use checkpoints to explain how cancer can arise.
Common mistakes
- Confusing positive and negative feedback.
- Forgetting DNA replicates in S phase (interphase), not mitosis.