Mitosis

• Prophase is the first stage of mitosis, during which the chromatin condenses into visible chromosomes.
• Our bodies begin as one cell and become an organism with more than a trillion cells.
• Cells must be continually regenerated and replaced
• Red blood cells only live for four months
• Injured tissue must be replaced
• As new cells are created, the genetic material must be passed on so

  that the new cells can carry out their functions.
• Genetics

  The field of biology that studies how genetic information is passed from one generation to the next.
• Recall Cell Theory:

  All living things are composed of one or more cells

  Cells are the smallest units of living organisms

  New cells come only from pre-existing cells by cell division
• Since all new cells come from existing

  cells, traits must be passed from a parent

  cell to the daughter cells.
• DNA is the mechanism through which these traits are passed.
• All somatic cells go through cell cycles.
• Each time a cell completes one cycle, it

  becomes two cells.
• There are three functions of cell division

  Growth of an organism

  Repair of damaged tissue

  Replace dead or dying cells
• Different cells have cycles with different

  durations

  Most animal cell cycles last 12-24 hours
• Three main stages

  Interphase

  Mitosis

  Cytokinesis
• Cell grows, develops, and copies its DNA
• Divided into G1, S, and G2 stages
• G1 – Growth 1

  Major period of growth
• S – Synthesis

  DNA is replicated

  DNA exists as chromatin
• G2 – Growth 2

  Final phase of interphase
• Chromatin condenses into

  chromosomes
• Each chromosome has two copies

  of parent DNA
• The two chromosome arms are called sister chromatids
• Joined by a centromere
• Nucleolus disappears

  Spindle fibres are formed from centrosomes
• Centrosomes move to opposite poles of the cell.
• Spindle fibres guide the

  chromosomes to the equator

  of the cell
• Spindle fibres attach to centromeres of

  each chromosome
• Sister chromatids are considered to be a

  single chromosome as long as chromatids

  are joined at the centromere
• Centromeres split apart
• Sister chromatids separate

  from each other
• Separated sister chromatids are now

  referred to as chromosomes
• Spindle fibres shorten and pull

  chromosomes to opposite poles of the cell
• Chromosomes begin to

  unwind into chromatin
• Spindle fibres break down
• Nuclear membrane begins to form around

  chromosomes
• Nuclear membrane begins to form around

  chromosomes
• Mitosis is the process of nuclear division
• Cytokinesis is the division of the cytoplasm

  to create two new daughter cells
• Indentation forms in the cell membrane along the equator of

  the cell. Indentation deepens until two cells are formed.