the cell cycle

Interphase Mitosis

Synthesis phase > DNA replicates semi-conservatively leading to two sister chromatids joined by a centromere Growth 1 and Growth 2 > Number of organelles increases Volume of cytoplasm increases Protein synthesis ATP content increased (order: G1, S, G2)

• Chromatin coils and condenses, becoming visible under a light microscope • Appears as two sister chromatids joined by a centromere • Nuclear envelope breaks down • Chromosomes free in cytoplasm • Centrioles move to opposite poles forming spindle network

Prophase Metaphase Anaphase Telophase Cytokinesis

• Chromosomes line up along the equator • Spindle fibres from each pole become attached to the centromeres of the chromosomes

• Spindle fibres contract • Centromere divides • Pairs of sister chromatids pulled to opposite poles of cell • Complete set of chromosomes at each pole • Energy (ATP) required

• Chromosomes uncoil, becoming longer and thinner • Chromosomes no longer visible under light microscope • Spindle fibres and centrioles break down • Nuclear envelope reforms around each group of nuclei

• Cytoplasm divides • Plasma membrane forms around two new genetically identical daughter cells

• Growth of multicellular organisms by increasing cell number • Repairing damaged tissues / replacing cells • Asexual reproduction

tumours and cancers

Malignant - cancerous, spreads and affects other tissues Benign - non-cancerous

Binary Fission

• Circular DNA and plasmids replicate • (circular DNA replicates once, plasmids can be replicated many times) • Cytoplasm expands as each DNA molecule moves to opposite poles of the cell • Cytoplasm divides • 2 genetically identical daughter cells, each with a single copy of DNA and a variable number of plasmids

• Viruses don’t undergo cell division as they are non-living • Attachment protein binds to complementary receptor protein on surface of host cell • Inject nucleic acid (DNA/RNA) into host cell • Infected host cell replicates the virus particles