The Cell Cycle

• Mitosis produces two genetically identical cells
• Mitosis replaces old cells and is how organisms repair and grow
• Meiosis produces four cells that contain half the number of chromosomes to that of normal cells, allowing fertilisation to occur
• Meiosis increases genetic variation in offspring
• Mitosis is a form of asexual reproduction, this type of reproduction produces two genetically identical daughter cells, known as clones.
• What type of reproduction is mitosis?

  Asexual
• Mitosis produces two cells that each have 23 pairs of chromosomes, these are known as diploid cells
• Diploid cells contain 23 pairs of chromosomes in humans
• Meiosis is a form of sexual reproduction, this type of reproduction produces four non-identical daughter cells, these are sex cells known as gametes
• What type of reproduction is meiosis?

  Sexual
• Meiosis produces gametes that have half the number of chromosomes of a diploid cell, so they are known as haploid cells
• Within multicellular organisms, not all cells retain the ability to divide, with eukaryotic cells that do retain that ability going through a process known as the cell cycle
• What is the cell cycle?

  A process that cells that can divide multiple times go through
• The cell cycle starts with a cell that has been produced by mitosis and ends when the cell is ready to divide
• Mitosis is a part of a precisely controlled process known as the cell cycle, which is the regulated sequence of events that occurs between one cell division and the next
• The length of the cell cycle varies depending on environmental conditions, the cell type and the organism
• What factors affect the length of the cell cycle?

  Environmental conditions, the cell type and the organism
• The movement from one phase to another is triggered by chemical signals called cyclins
• What are the chemical signals called that trigger the movement of phases?


  Cyclins
• What are the three main sections of the cell cycle?

  Interphase, mitosis and cytokinesis
• Interphase is the phase between divisions, in which the DNA is unwound as chromatin so that the genes are accessible for transcription.
• Cell growth, also known as elongation and DNA replication happens during interphase.
• During interphase, the amount of ATP being produced is increased as energy is required for cell division
• Interphase takes up approximately 90% of the cell cycle and is split up into three phases: G1, S and G2
• What are the phases of interphase?

  G1, S, G2
• What does G1 stand for?

  Growth 1
• What happens during G1 phase?

  A signal is received, telling the cell to divide again, new organelles are formed, new proteins synthesised and therefore causes cell growth to occur.
• What does S phase stand for?

  Synthesis phase
• What happens during S phase?

  DNA replication, causing the amount of DNA to double
• What does G2 stand for?

  Growth 2
• What happens in G2 phase?

  Cell undergoes another growth stage, where new organelles are formed, new proteins are synthesised and the cell grows
• In the G2 phase, the new DNA that has been synthesised is checked and any errors are usually repaired
• Specialised cells and stem cells can move from G1 into a resting phase known as G0, this can be temporary.
• Mitosis is the process of nuclear division by which two genetically identical daughter nuclei are produced that are genetically identical to the parent cell nucleus (they have the same number of chromosomes as the parent cell).
• What is mitosis?


  The process of nuclear division by which two genetically identical daughter nuclei are produced
• The process of mitosis is of great biological significance and is fundamental to many biological processes.
• Why is mitosis important?

  • The growth of multicellular organisms
  • Replacement of cells and repair of tissues
  • Asexual reproduction
• The two daughter cells produced by mitosis enables unicellular zygotes to grow into multicellular organisms
• Growth may occur across the whole body of the organism or be confined to certain regions, such as in the meristem of plants, this is where mitosis occurs
• Damaged tissues can be repaired by mitosis followed by cell division