The cell cycle

The cell cycle is a series of events that a cell goes through as it grows and divides. You need to understand the cell cycle to grasp how organisms grow, repair tissues, and stay healthy. Use this resource to learn about the cell cycle.

The cell cycle consists of several phases: interphase, mitosis and cytokinesis. We can compare these phases to preparing for and executing a theatrical play.

Interphase

Interphase is like the rehearsal period before the big night. During this time, all the necessary planning, growth and organisation occur to make sure everything is ready for the show. It is when the cell grows and its genetic material (DNA) is replicated.

Interphase is the longest phase in the cell cycle. It consists of three stages:

1. G1 – The cell grows and carries out regular metabolic functions.
2. S – DNA replication occurs to make sure that each new cell has an identical set of genetic material. The centrosome also duplicates.
3. G2 – The cell continues to grow and produce what it needs to mitosis.

Interphase is crucial for make sure the cell has all the parts it needs to divide successfully and accurately.

The stages of interphase as shown in the figure.

Mitosis

Mitosis is like the performance night. All the preparations made during interphase come together—the actors take the stage, deliver their lines and the story unfolds in front of an audience. Just as the play transitions through various scenes and acts, mitosis involves a series of stages where the cell divides its replicated DNA and splits into two identical daughter cells.

Mitosis consists of several stages:

1. prophase – The chromosomes condense and the nuclear envelope begins to dissolve. "Pro" means "before", so you can think of it as the stage before the chromosomes start to move.
2. metaphase – The chromosomes align along the equator of the cell. "Meta" means "in between", so it is the middle stage. You might also like to think of it as when the chromosomes are lined up between the centrosomes.
3. anaphase – The sister chromatids are pulled apart by spindle fibres to opposite sides (or poles) of the cell. "Ana" means "backwards", referring to the pulling of chromatids back to the poles.
4. telophase – The nuclear envelope reforms around the separated chromosomes and the chromosomes recondense. "Telo" means "end", so it is the phase at the end of cell division.

Mitosis makes sure that each daughter cell has an exact copy of the parent cell's DNA, maintaining genetic consistency across cell generations.

The stages of mitosis are shown in the figure.

Use this mnemonic to remember the order of the phases in mitosis: Post Memes And Tiktoks.

Cytokinesis

In the theatrical play analogy, cytokinesis would be like the stage crew closing the curtains and preparing for the next show. After the actors have finished their performance (mitosis), the stage is carefully reset and divided, ensuring everything is neatly organised. This process ensures that the two separate "productions" (or cells) are ready for future events.

Cytokinesis is the final step of the cell cycle, where the cell's cytoplasm divides to form two distinct daughter cells.

• In animal cells, the cell membrane pinches inwards, creating a groove that eventually splits the cell in two.
• In plant cells, a new structure called a cell plate forms in the middle, which becomes the new cell wall separating the two daughter cells.

Cytokinesis ensures that each daughter cell receives not only an equal and complete set of genetic material but also the necessary organelles and resources to function independently.

Summary

The cell cycle is summarised in the figure.

Exercise

See how well you understand the cell cycle with a quick quiz.

Data drill

Read the scenario and use the information provided to answer the questions in the quiz.

Telomeres are protective caps on the ends of chromosomes that protect the DNA from damage. They also play important roles in DNA replication.

Researchers at the Institute of Dee and Aye published a study looking at telomere length and human aging. Telomere length in white blood cells was plotted against age, in years, and the p- and r-values are shown.

Images on this page by RMIT, licensed under CC BY-NC 4.0