M2:S6 Cell division and cellular organisation

• The Cell Cycle


  Cell growth and division
• G2 Checkpoint


  • Cell checks whether all DNA has been replicated without damage before entering mitosis
• Interphase


  Cell keeps growing and makes proteins needed for cell division
• Synthesis


  Cell replicates its DNA, ready to divide by mitosis
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Mitosis is needed for growth of multicellular organisms and repairing damaged tissues, and is a method of asexual reproduction for some organisms
• Mitosis is a continuous process described in stages
• Interphase


  Cell carries out normal functions and prepares to divide by replicating DNA and organelles, and increasing ATP content
• Prophase


  Chromosomes condense, centrioles move to opposite ends forming spindle, nuclear envelope breaks down
• Metaphase


  Chromosomes attach to spindle and line up at the equator, metaphase checkpoint checks all chromosomes are attached
• Anaphase


  Centromeres divide, sister chromatids separate and move to opposite poles
• Telophase


  Chromatids reach opposite poles, uncoil into chromosomes, nuclear envelope reforms around each set
• Cytokinesis


  Cytoplasm divides, forming two genetically identical daughter cells
• Chromosomes can be stained to observe the cell cycle and mitosis under a microscope
• Interphase cells have spread out, uncondensed chromosomes
• Meiosis produces gametes for sexual reproduction
• Meiosis


  A type of cell division that reduces the chromosome number by half to produce gametes
• Meiosis I


  1. Prophase I

  2. Metaphase I

  3. Anaphase I

  4. Telophase I
• Meiosis II is similar to mitosis, producing four genetically different haploid daughter cells
• Homologous chromosomes


  • Pairs of chromosomes, one from each parent, that are the same but may have different alleles
• Crossing over


  Homologous chromosomes pair up and swap sections of chromatids in prophase I
• Crossing over and independent assortment of chromosomes during meiosis lead to genetic variation in the gametes
• Haploid


  Having half the normal number of chromosomes
• Stem cells are unspecialised cells that can develop into different cell types
• Stem cells are found in early embryos and in limited places in adults
• Embryonic stem cells can develop into any cell type, while adult stem cells can only develop into a limited range
• Genetic variation in daughter cells

  Occurs because of two processes: crossing over and independent assortment
• Stem cells are unspecialised cells
• Multicellular organisms are made up of many different specialised cell types
• All specialised cell types originally came from stem cells
• Stem cells can develop into different types of cells
• All multicellular organisms have some form of stem cell
• In humans, stem cells are found in early embryos and in a few places in adults
• Stem cells in early embryos can develop into any type of human cell
• Stem cells in adults can only develop into a limited range of cells
• Stem cell differentiation


  1. Stem cells divide to become new cells

  2. New cells become specialised
• Differentiation


  The process by which a cell becomes specialised for its job
• In animals, adult stem cells are used to replace damaged cells
• Plants are always growing, so stem cells are needed to make new shoots and roots throughout their lives
• Stem cells can differentiate into various plant tissues including xylem and phloem