5.1 Cell Cycle and Mitosis Chapter 5 notes

Cell cycle overview

Life Cycle of a cell 1. Interphase – longest stage (80% of the time) where the cell carries out its various functions Growth and preparation – cell increases in size and makes proteins and molecules to function; some organelles duplicate  replication– DNA copies itself (all 3 billion bases!) Fig 5.5 DNA molecule unwinds and “steps” of ladder break apart (enzymes help out with this) New bases pair with bases on original DNA Two new identical DNA molecules are produced Continued growth and preparation – makes more proteins for the new cell that will be formed; mitochondria and chloroplasts duplicate

Visual overview of mitosis

Mitosis – early prophase 2. Mitosis – shortest stage where the contents of the nucleus divides resulting in two daughter nuclei; sister chromatids are joined by the centromere (fig 5.7) Early prophase Replicated chromosomes coil up into X-shaped chromosomes and become visible  nucleolus disappears and nuclear membrane begins to break down Spindle fibres (tube like proteins) begin to form and stretch across the cell from organelles

Late prophase and metaphase Spindle fibres complete forming Chromosomes attach to spindle fibres at the centromere Nuclear membrane disappears Metaphase Spindle fibres pull the x-shaped chromosomes into a single line across the middle of the cell

Anaphase and telophase Spindle fibres contract and shorten which pulls the centromere apart Sister chromatids move to opposite poles of the cell Once separated, each sister chromatid is considered to be a chromosome  Telophase One complete set of chromosomes at each pole of the cell  Spindle fibres disappear and nuclear membrane forms around each set of chromosome Nucleolus appears within each nucleus  Cell is ready to divide

Cytokinesis and checkpoints 3. Cytokinesis – separates the two nuclei into two daughter cells Animal cells – the cell membrane pinches together to divide Plant cells – cell plate forms along the centre of the cell Checkpoints Cells will not divide if... There are not enough nutrients to support cell growth  DNA within the nucleus has not been replicated  DNA is damaged

Cancer Uncontrolled cell division (checkpoints don’t work) Healthy cells stop dividing when they receive a message from neighbouring cells but cancer cells don’t Cancer cells don’t function the same as other cells but they can release chemicals to attract nearby blood vessels to branch into the tumour to feed it Blood vessels can carry cancer cells to new places in the body