PapaMarks
Library › Biology 9700 › The Mitotic Cell Cycle
AS Level · Biology 9700

The Mitotic Cell Cycle

Revise The Mitotic Cell Cycle for Biology 9700 (AS Level) — revision notes and instant AI marking.

📖 Revision notes · preview
  Cambridge International AS & A Level Biology (9700)

The Mitotic Cell Cycle

The big idea: A cell copies its DNA in interphase and then shares it out exactly in mitosis, so both daughter cells are genetically identical. Telomeres protect genes, stem cells supply replacements, and loss of control produces tumours.

Summary — What This Chapter Covers
  • Chromosome structure: DNA, histones, sister chromatids, centromere, telomeres.
  • Mitosis for growth, replacement, repair and asexual reproduction.
  • The cell cycle: G1, S, G2, mitosis and cytokinesis.
  • Telomeres preventing loss of genes during replication.
  • Stem cells in cell replacement and tissue repair.
  • Uncontrolled cell division and tumour formation.
  • Chromosome behaviour in prophase, metaphase, anaphase and telophase; identifying stages.
1. Replication and division of nuclei and cells
Chromosomes

Structure of a chromosome

  • DNA: one very long DNA molecule per chromatid.
  • Histone proteins: the DNA is wound around histones, which package it and allow it to coil tightly (condense) before division. DNA plus histones is called chromatin.
  • Sister chromatids: after DNA replication each chromosome consists of two genetically identical chromatids.
  • Centromere: the region where the two sister chromatids are held together, and where spindle microtubules attach.
  • Telomeres: repeated, non-coding base sequences at the ends of each chromatid.
Why mitosis matters

Genetically identical daughter cells

Mitosis is nuclear division that produces two daughter nuclei with the same number of chromosomes as the parent and genetically identical to it. This is important for:

  • Growth of multicellular organisms: increasing the number of cells, each with the same genetic information.
  • Replacement of damaged or dead cells, e.g. skin, the lining of the gut, red blood cells.
  • Repair of tissues by cell replacement, e.g. wound healing.
  • Asexual reproduction, e.g. budding in yeast, potato tubers: offspring are identical to the parent.
Cell cycle

Interphase, mitosis and cytokinesis

PhaseWhat happens
G1 (interphase)Cell grows; makes proteins (including enzymes for replication) and organelles; carries out normal functions
S (interphase)DNA replication: each chromosome becomes two sister chromatids; histones are made
G2 (interphase)Further growth; organelles (e.g. mitochondria, centrioles) duplicated; energy stores built up for division; DNA checked
MitosisNuclear division: prophase, metaphase, anaphase, telophase
CytokinesisDivision of the cytoplasm to form two daughter cells

The mass of DNA per cell doubles during S phase (e.g. from x to 2x) and halves back to x at cytokinesis.

Worked Example

In a root tip squash, 300 cells were counted: 270 in interphase, 18 in prophase, 6 in metaphase, 3 in anaphase and 3 in telophase. The cell cycle lasts 20 hours. Estimate the time spent in mitosis and in metaphase.

Telomeres and stem cells

Protecting genes and replacing cells

Telomeres

shorter at each replication genes are not lost

Stem cells

stem cell differentiate

Cancer

Uncontrolled cell division and tumours

  • The cell cycle is controlled by genes, for example ones that stimulate division and others that stop it (tumour suppressor genes).
  • mutation
  • tumour
  • benign malignant metastasis
🔓 Read the full The Mitotic Cell Cycle note → You're seeing the preview · sign in to read it all
Also in the full note
  • Prophase, metaphase, anaphase, telophase
  • Reading photomicrographs and slides
What's inside
📖 Revision notes 🎯 Learn mode ✦ AI flashcards ✓ Instant AI marking 🧊 3D explorers 🧪 Experiments & simulations 📈 Progress tracking
📄 Practise The Mitotic Cell Cycle with Biology 9700 past papers Every paper with its mark scheme — answer online, marked instantly. Open →

Read the full The Mitotic Cell Cycle notes free

That's the preview — create a free account to read the rest, plus flashcards and practice questions with instant AI marking. No credit card.

Unlock the full notes free →

More Biology topics

Cell Structure
The gas exchange system
The circulatory system
Mode of action of enzymes
Fluid mosaic membranes
Replication and division of nuclei and cells
Structure of nucleic acids and replication of DNA
Testing for biological molecules
Structure of transport tissues
The microscope in cell studies