all cells arise from other cells

• what are the 2 main stages of cell division

  nuclear division and cytokinesis
• what is nuclear division?

  the process in which the nucleus divides
• what is cytokinesis?

  the process by which the whole cell divides (the cytoplasm divides into daughter cells
• What are the steps of semi conservative DNA replication?

  - the enzyme DNA helicase unwinds and separated the DNA double helix, breaking the hydrogen bonds between complementary base pairs

  - both strands then act as a template for DNA replication

  - free activated DNA nucleotides hydrogen bonds between complementary to their complementary base pairs on the template strand

  - DNA polymerase catalyses the formation of phosphodiester bonds between adjacent nucleotides

  - this results in 2 identical DNA molecules which contain 1 newly synthesised strand and 1 original strand
• What is the importance of cell division?

  - growth

  - repair and replacement

  - reproduction
• what is the definition of mitosis?

  Nuclear division that produces 2 daughter nuclei that are genetically identical to the parent nuclei as well as eachother
• what stage of mitosis does DNA replication occur

  Interphase
• What are the 4 stages of mitosis

  - prophase

  - metaphase

  - anaphase

  - telophase
• what are centrioles

  Small hollow cylinders that form a network of fine fibres in the cytoplasm called the cytoskeleton
• What is the function of the centrioles

  - support the cells shape

  - organises and moves organelles

  - during cell division the pair separate to opposite ends of the cell and form the spindle
• describe prophase

  - longest phase

  - chromosomes condense and become visible

  - centrioles move to opposite poles of the cell

  - spindle fibres start to develop

  - nuclear envelope disintegrates and nucleolus disappears
• describe metaphase

  - chromosomes attach to spindle fibres by their centromeres

  - they line up at right angles along the equator of the cell
• describe anaphase

  - very fast

  - centromeres divide into 2

  - spindle fibres shorten and pull chromatids to opposite poles of the cell, centromeres first
• describe telophase

  - chromatids have reached the poles and are referred to as chromosomes again

  - chromosomes begin to lengthen and uncoil and loose visibility

  - spindle disintegrates

  - nuclear envelope reforms and nucleolus disappears

  - nuclear division is complete
• describe how viruses replicate

  Virus attaches to host cell via receptors on the host cell surface membrane

  The virus injects its genetic material into the host cell and this is used to synthesise viral proteins

  New virus particles are assembled

  New viruses burst out of, and damage/destroy the host cell