[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Histology](https://durgical.com/en/histology/) › [The cell](https://durgical.com/en/histology/#a-cell) › Cell cycle, mitosis and meiosis

[Histology](https://durgical.com/en/histology/) · [The cell](https://durgical.com/en/histology/#a-cell)

# Cell cycle, mitosis and meiosis

- Process

The cell cycle is the sequence by which a cell grows, copies its DNA and divides; its brakes fail in cancer.

Updated 2026-11-01

**See it in 3D:** [Testes](https://durgical.com/en/anatomy/testis/) · [Skin](https://durgical.com/en/anatomy/skin/)

## Key points

- Rb brakes G1/S; cyclin D-CDK4/6 phosphorylates it so the cycle can proceed.
- p53 stops the cycle in G1 or triggers apoptosis when DNA is damaged.
- Proto-oncogenes = accelerator; tumour suppressor genes = brake.
- Meiosis I separates homologues (halves to haploid); meiosis II separates chromatids.
- HPV: E6 against p53, E7 against Rb.

## What it is

The cell cycle has an interphase (G1, S and G2) and an M phase of division. Checkpoints make sure the DNA is intact and fully copied before the cell moves on. Mitosis makes two identical cells; meiosis, in the gonads, makes four different haploid gametes. Oncogenes and tumour suppressor genes control the process.

## Step by step

- G1: the cell grows and does its job; this is the phase whose length varies most. Cells that stop dividing exit to G0.
- G1/S checkpoint: cyclin D with CDK4/6 phosphorylates Rb, which releases E2F and lets the cell enter S; p53 halts it if DNA is damaged.
- S: DNA is replicated and each chromosome ends up with two sister chromatids.
- G2: the cell checks the copy and gets ready to divide.
- Prophase and prometaphase: chromosomes condense, the nucleolus disappears, the nuclear envelope breaks down and the spindle forms.
- Metaphase: chromosomes line up on the equatorial plate; the spindle checkpoint requires every one to be attached to microtubules.
- Anaphase: sister chromatids move apart to the poles.
- Telophase and cytokinesis: two nuclei form and a ring of actin and myosin divides the cytoplasm.

## Mitosis versus meiosis

| Feature | Mitosis | Meiosis |
| --- | --- | --- |
| Where | Somatic cells | Germ cells (testis, ovary) |
| Divisions | One | Two (meiosis I reductional, meiosis II equational) |
| Result | Two identical diploid cells | Four different haploid cells |
| Recombination | No | Yes, crossing over in prophase I |
| Classic error | Aneuploidy in tumours | Nondisjunction: trisomy 21, usually in maternal meiosis I |

## Clinical notes

- High-risk HPV: the E6 protein degrades p53 and E7 inactivates Rb, removing the cycle's brakes and leading to cervical cancer.
- Many anticancer drugs act in one phase: antimetabolites in S; vinca alkaloids and taxanes in M.
- Mature neurons and cardiac myocytes sit in G0: they barely regenerate by division.

## In the lab

- Under the microscope a mitotic figure looks like very dark, condensed chromatin with no nuclear envelope; in metaphase, like a band or plate.
- The mitotic index and Ki-67 immunohistochemistry estimate how many cells in a tumour are dividing.
- Atypical mitoses (tripolar, for example) suggest malignancy.

## Memory aid

E6 sacks the guardian, E7 bribes the gatekeeper: p53 guards the genome and Rb keeps the G1/S gate.

## Test yourself

Think of the answer, then tap the question to see it.

## What does the Rb protein do in the cell cycle?

It holds the E2F factor and brakes entry into S phase; once phosphorylated by cyclin D-CDK4/6 it releases E2F and the cycle moves on.

## In which phase is DNA copied?

In the S phase of interphase.

## Which HPV proteins inactivate p53 and Rb?

E6 promotes the breakdown of p53 and E7 binds and inactivates Rb.

## In which meiotic division do homologous chromosomes separate?

In meiosis I, which halves the chromosome number.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/histology/cell-cycle-mitosis-and-meiosis/)

## See it in 3D

The structures of Durgical's 3D anatomy where it is found.

- [Testes](https://durgical.com/en/anatomy/testis/)
- [Skin](https://durgical.com/en/anatomy/skin/)

## Related

- [Cytoskeleton: microfilaments, intermediate filaments, microtubules](https://durgical.com/en/histology/cytoskeleton-microfilaments-intermediate-filaments-microtubules/)
- [Cell injury, apoptosis and necrosis](https://durgical.com/en/histology/cell-injury-apoptosis-and-necrosis/)
- [Cell adaptations: hypertrophy, hyperplasia, atrophy, metaplasia](https://durgical.com/en/histology/cell-adaptations-hypertrophy-hyperplasia-atrophy-metaplasia/)
- [Testis: seminiferous tubules, Sertoli and Leydig cells, spermatogenesis](https://durgical.com/en/histology/testis-seminiferous-tubules-sertoli-and-leydig-cells-spermatogenesis/)

## Related conditions

- [Cervical cancer](https://durgical.com/en/conditions/cervical-cancer/)
- [Human papillomavirus (HPV) infection](https://durgical.com/en/conditions/human-papillomavirus-infection/)

## Microorganisms

- [Human papillomavirus](https://durgical.com/en/microbiology/human-papillomavirus/)

## In Pharmacology

- [Vincristine](https://durgical.com/en/pharmacology/vincristine/)
- [Paclitaxel](https://durgical.com/en/pharmacology/paclitaxel/)
- [Methotrexate](https://durgical.com/en/pharmacology/methotrexate/)

[← All of histology](https://durgical.com/en/histology/)

Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: [3.5 Cell Growth and Division](https://openstax.org/books/anatomy-and-physiology-2e/pages/3-5-cell-growth-and-division) (OpenStax (Rice University), 2022); [What Is Cancer?](https://www.cancer.gov/about-cancer/understanding/what-is-cancer) (National Cancer Institute, 2021).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/histology/cell-cycle-mitosis-and-meiosis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/histology/cell-cycle-mitosis-and-meiosis/