4.4.6Additional lessons
Cell Cycle — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 45 of 101
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Stages of the Cell Cycle
G1, S and G2 together make up interphase, which is the longest part of the cycle.
1
G1 phase: the cell grows, makes proteins and organelles and carries out its normal functions.
2
S phase: the whole genome is replicated, so that each chromosome becomes two sister chromatids.
3
G2 phase: the cell grows further, checks the copied DNA and makes the proteins needed for mitosis.
4
M phase: mitosis divides the nucleus and cytokinesis divides the cytoplasm.
5
Cells that stop dividing leave the cycle in G1 and enter a resting state called G0.
Part 2 of 5Activities During Interphase
DNA replication
- DNA replication Occurs in S phase and is semi-conservative, producing two identical DNA molecules from each original one.
Protein synthesis
- Protein synthesis Enzymes, histones and spindle proteins are made, supporting growth and preparing for division.
Organelle production
- Organelle production Mitochondria and chloroplasts divide and ribosomes are made, so each daughter cell gets enough of them.
Respiration
- Respiration ATP production continues at a high rate to power synthesis and later the movement of chromosomes.
Part 3 of 5Control of the Cycle
Checkpoints stop the cycle if something is wrong, preventing damaged cells from dividing.
Cyclins
- Cyclins These proteins rise and fall in concentration during the cycle, so they act as signals that mark each stage.
CDKs
- CDKs Cyclin-dependent kinases are enzymes that are active only when bound to a cyclin, and they phosphorylate other proteins to drive the next stage.
G1/S checkpoint
- G1/S checkpoint The cell checks size and DNA damage before copying its DNA, and damaged cells can be held back or sent to die.
G2/M and spindle checkpoints
- G2/M and spindle checkpoints The cell checks that replication is complete and later that all chromosomes are attached to the spindle before anaphase.
| Phase | Main event | Part of interphase? |
|---|---|---|
| G1 | Growth and normal function | Yes |
| S | DNA replication | Yes |
| G2 | Preparation for mitosis | Yes |
| M | Mitosis and cytokinesis | No |
Part 4 of 5Why Control Matters
Growth regulation
- Growth regulation The rate of division is matched to the needs of the tissue, so organs stay the correct size.
Genome integrity
- Genome integrity Checkpoints reduce the chance of passing a mutation to daughter cells.
Link to cancer
- Link to cancer Loss of control through mutation in the genes that code for cell cycle proteins can lead to tumours.
Part 5 of 5Exam Checklist & Tips
4.4.6 – Key Points for the Exam
- Interphase The part of the cell cycle between divisions, made up of G1, S and G2.
- Cyclin A protein whose concentration varies through the cycle and activates CDKs.
- Checkpoint A control point where the cell cycle halts unless conditions are suitable.
- G0 A phase where a cell has left the cycle and no longer divides.
Common Mistakes
- Calling interphase a resting phase; the cell is metabolically very active.
- Placing DNA replication in G1 or G2 instead of S phase.
- Saying cyclin levels stay constant through the cycle.
- Believing mitosis is the longest phase; interphase takes most of the cycle.
Last updated:
Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.