The Cell Cycle | A-level Biology | OCR, AQA, Edexcel

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The key points covered of this video include:

1. Interphase, Mitosis, and Cytokinesis
2. Interphase - G1
3. Length of G1
4. Interphase - S and G2
5. Exiting the Cell Cycle

Interphase, Mitosis, and Cytokinesis

When looking at cell tissue down a microscope, we see some cells which are dividing and some which are not. It turns out that lots of cells in multicellular tissue don't have the ability to divide. Even cells that can divide go through a long period of not dividing . This phase is called interphase. After this the chromosomes start to appear and move to opposite parts of the cell - this is called mitosis. Then the cell splits in two - this is called cytokinesis. This process is repeated again and again - which we refer to as the cell cycle.

Interphase - G1

In interphase, cells may look like they're dormant - but this is an important stage in the cell cycle. Interphase is split up into three stages: G1, S, and G2. In G1 (or the growth phase) preparations are made to ensure the cell is ready to go into S phase. These preparations include duplicating organelles, growing in size, and making proteins that will be needed in S phase.

Interphase S & G2

Now the cell is ready to enter S phase, after which there is no going back - the cell has to complete the cell cycle. This is also called the synthesis phase because this is when DNA synthesis happens. The more important sequences of DNA are replicated first and the bits of DNA that are only required in some cell types are replicated last. At the end of S phase all the chromosomes will be replicated. The last part of interphase (G2) involves a series of checks and preparations to make sure the cell is ready for mitosis. This includes activating proteins involved in the first stage of mitosis.

Length of G1

The length of the cell cycle is different in different cell types. This is because of the G1 phase - which can be shorter or longer depending on the cell type. Liver cells divide very slowly and have a long G1 phase whilst cells of the stomach lining have a short G1 phase.

Exiting the Cell Cycle

Cells that don't divide have - at one point - left the cell cycle. This occurs early in the G1 phase - cells here can either continue in the cell cycle or enter the G0 phase. Cells in the G0 phase may differentiate, die, or enter senescence (where they stop dividing).

Summary

The cell cycle consists of Interphase, Mitosis, and Cytokinesis
The cell increases in mass through interphase and mitosis until it splits into two in cytokinesis
The mass of DNA increases in part of interphase, it splits into two cells in cytokinesis