CELL CYCLE

• Binary fission


  Method of cell replication used by prokaryotes (asexual reproduction)
• Asexual reproduction


  A method of reproduction that produces genetically identical cells without the fusion of gametes
• Plasmids


  Small, circular loop of DNA that is separate from a chromosome
• Septum


  Dividing wall formed during binary fission
• Generation time


  Time taken for a population of bacteria to divide
• Purpose of cell replication


  • Growth and development
  • Maintenance and repair
  • Reproduction
• Cells don't become larger, we are made of more cells
• Cell replication allows damaged cells to be replaced to ensure proper functioning
• Cells replicate to reproduce, enlarging their population when they reproduce
• Exponential growth


  Cell replicates exponentially, after each round of replication, number of cells double
• Binary fission


  1. DNA replication

  2. Elongation

  3. Septum formation

  4. Cell division
• Circular chromosome is uncoiled and the DNA is replicated. Plasmids replicate.
• Cell elongates to prepare cell to separate into 2 new cells and duplicated circular chromosomes migrate to opposite ends
• Cell begins to undergo cytokinesis (process of separating into 2 new cells); by pinching inwards and creating a septum.
• New cell wall formed in the centre
• 2 genetically identical cells are formed
• DNA


  A nucleic acid molecule found in the nucleus of all cell, carries instructions for making proteins
• Gene


  Section of DNA that has instructions for making proteins
• Chromosome


  Long organised strand of DNA. Humans have 46
• Mutation


  Change in DNA sequence that affects function of protein it codes for
• Somatic cell


  Any cell that is not reproductive (two sets of chromosomes/diploid)
• Cleavage furrow


  Indentation in plasma membrane
• Centrioles


  Composed of protein which form spindle fibres
• DNA is made up of nucleotides and has double helix shape
• Order of bases along the DNA strand that holds instructions for making proteins
• Interphase


  1. Cellular growth and duplication of chromosomes

  2. Synthesises necessary DNA, protein organelles required for replication

  3. DNA exists as long chromatin threads
• Interphase substages


  • G1 phase
  • S phase
  • G2 phase
• If further replication not needed, cell exit cell cycle in G1 and go to rest (G0)
• G1 phase


  Cell grows by increasing volume of cytosol and synthesising protein for DNA replication
• S phase


  Cell replicates its DNA by turning one chromosome into two identical sister chromatids, held together by a centromere
• After S phase, each somatic cell still has 46 chromosomes
• G2 phase


  Cell continues to grow and prepare itself for mitosis, increasing the volume of cytosol and synthesising proteins
• Mitosis


  Separation of sister chromatids and the formation of 2 new nuclei
• Mitosis stages


  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• In prophase, the nuclear membrane disappears, chromosomes condense into visible and discrete chromosomes, and the centrioles form and migrate to opposite poles of the cell and spindle fibres begin to form
• In metaphase, spindle fibres fully form and attach to the centromeres, allowing spindle fibres to guide the chromosomes to line up at the equator of the cell
• In anaphase, spindle fibres contract, splitting centromere and pulling sister chromatids to opposite ends of cell
• In telophase, chromosomes densely pack together, new nuclear membranes form, producing 2 genetically identical nuclei, and spindle fibres disintegrate and chromosomes condense
• Cytokinesis


  Division of cytoplasm and formation of 2 daughter cells
• Cytokinesis in animal vs plant cells


  • Animal cells: Formation of a cleavage furrow that pinches plasma membrane into 2 cells
  • Plant cells: Cell plate first forms at equator before closing and separating into 2 new cells