Mitosis and the cell cycle

• In the nucleus we find chromosomes, which are made of the molecule DNA. Like this...

  
• Body cells contain two of each chromosome. They are paired. Like this...

  
• Human body cells contain 23 pairs of chromosomes. However, gametes have chromosomes which are not paired. (Human gametes have 23 single chromosomes).
• Chromosomes carry a large number of genes which determine many of our features. These chromosomes only have 4 genes, but human chromosomes contain hundreds. Like this...

  
• Cells have to be able to divide. That is called the cell cycle.
• In the first stage of the cell cycle, the DNA replicates to form two copies of each chromosome. Like this...

  
• The cell also grows and copies its internal structures such as mitochondria and ribosomes. Like this...

  
• In the second stage of the cell cycle, mitosis takes place. One set of chromosomes is pulled to each end of the cell. The nucleus also divides. Like this...

  
• In the final stage of the cell cycle, the cytoplasm and the cell membrane divide to form two identical cells. Like this...

  
• At the start, we had one cell which had two pairs of chromosomes and at the end we've got two identical cells, again each with two pairs of chromosomes. Like this...

  
• Functions of mitosis:

  1. Mitosis is essential for growth and development of multicellular organisms (e.g. plants and animals).
  2. Mitosis takes place when an organism repairs itself (e.g. when a broken bone heals).
  3. Mitosis happens during asexual reproduction.
• 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:

  
• Mitosis (part 1):

  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.
• Mitosis (part 2):

  • 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 (part 1):

  
• Diagram showing the process of cell division by mitosis (part 2):