Structure, function and growth of prokaryote and eukaryote cells (ii) Cell growth and Cell cycle Interphase Mitosis Mitotic index Control of the cell cycle Abnormal Cell division: cancer cells

Cell Cycle When cells reach a certain size they must stop growing or divide. The cell cycle is the period from the formation of a new cell until that cell divides itself The length of the cycle depends on the cell – but is usually 8 – 20 hours

The Cell Cycle CK

Interphase… G 1 (First Gap Period)  Cell grows and increases in mass Cell membrane (+ wall) are increased Number of organelles increase Chemical preparation for DNA Synthesis (enzymes, deoxyribose sugars, nucleotide bases and phosphates synthesised)

Interphase S phase (synthesis)  Replication of DNA Chromosomes held together by centromere  In animals centriole pairs duplicate

Interphase G 2 (Second gap phase)  Cell builds up energy reserves  Increased protein synthesis

Mitosis Revision – complete the mitosis diagram (note this is from standard grade)

Mitosis Compare this to your SG diagram. Name the stages  Interphase  Prophase  Metaphase  Telophase  Cytokinesis What features characterise each stage?

Mitosis Prophase  Chromosomes condense (coil and fold up) to become visible. Joins onto spindle fibre Chromatids in condensed form

Mitosis – prophase cont…  Cytoskeleton disintegrates (its components (microtubules) are used to begin spindle formation)  Spindle formation begins between centrosomes (aka Microtubule organising centres – MTOCs)  Nuclear Membrane starts to break up

Mitosis – prophase cont…

Mitosis Metaphase  Spindle continues to grow from centrosomes (which are now at the poles)  Chromosomes line up across the centre of the cell

Mitosis – metaphase cont..  Chromosomes attach to the spindle fibre by the kinetochore in the centromere  The arrangement of the chromosomes across the equator is also known as the metaphase plate.

Mitosis – metaphase cont…

Mitosis Anaphase  Centromeres divide  Sister chromatids separate and the chromosomes are pulled to the poles

Mitosis – anaphase cont…

Mitosis Telophase  Chromosomes begin to de-condense  Nuclear membrane reforms  Spindle disassembles and reassembles as the cytoskeleton in the 2 new cells

Mitosis – telophase cont…

Cytokinesis Dividing of the cytoplasm and organelles Animals  Cytoplasm is pinched by a ring of contractile microfilaments (made up of the proteins actin and myosin)  As the ring gets smaller it forms a cleavage furrow

Cytokinesis cont…

In plants  Membrane vesicles spread across the equator of the cell.  They merge to form plasma membrane  The new membranes lay down the cell wall between the two cells.

Cytokinesis cont…

Mitotic Index The fraction (or percentage) in a microscope field that contain condensed chromosomes (i.e. Undergoing mitosis)

Learning Activities Look at web animations  Cell biology – Mitosis / Meiosis – How cells divide Posters Card sort (pictures / names / descriptions) Read Dart pg 9-14 and take notes Use Scholar Advanced Higher Questions