Mitosis & the Cell Cycle (OCR Gateway GCSE Biology: Combined Science)

• The cell cycle can be thought of as the life cycle of a cell
• It is the series of growth and development steps a cell undergoes
  • From its formation to the point it divides to make new cells
• The cells in your body need to be able to divide to help your body grow and repair itself
  • Cells grow and divide over and over again
  • For this to happen the DNA has to be copied
• All body cells (except gametes) are produced by mitosis which happens as part of the cell cycle

There are 3 parts of the cell cycle

• Interphase - consists of phases of cell growth and synthesis of new DNA
  • Just before mitosis, the DNA in the nucleus copies itself exactly (forming duplicate chromosomes)
• Mitosis - Chromosomes line up along the centre of the cell and are pulled apart
• Cytokinesis - The cell cytoplasm and membrane divides to produce two daughter cells
  • Each new cell has a copy of each of the chromosomes

The three stages of the cell cycle

• The process of mitosis is itself made up of a series of stages that begin after interphase has occurred
  • DNA was copied during interphase to produce duplicate chromosomes 
• During mitosis, the sets of duplicated chromosomes line-up in the centre of the cell
• Cell fibres attach to the duplicated chromosomes and pull them apart
• One chromosome arm (chromatid) from each set is pulled to each end of the cell
• A new nucleus forms around each group of chromosomes
• After this, the cytoplasm and cell membranes divide in a process known as cytokinesis. This results in the formation of two genetically identical daughter cells

Diagram showing the process of cell division by mitosis