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1.6: Cell division

Mitosis

Defined as: division of a nucleus into two genetically identical daughter nuclei.

When does mitosis occur?

1. Growth (incl. embryonic development)

2. Repair

3. Asexual reproduction

IP

MA

TCtelophase

interphase

metaphase

anaphase

prophase

cytokenesis

Before…DNA is replicated, cell makes a complete copy of it’s genetic material (Interphase).

Each chromatid has an identical copy (sister chromatid)

Sister chromatids are attached at the centromere

Prophase

Chromosome become visible – shorter & coil

Homologous chromosomes (homologues) pair up – maternal & paternal chromosomes are side by side (their formation is known as synapsis)

Spindle fibers made from microtubules form.

MetaphaseBivalents (paired homologous chromosomes) line up along equator

Nuclear membrane disappears

Spindle attaches to centromere

Anaphase

Spindle fibers from poles attach to chromosomes

Spindle fibers pull chromosomes to the poles of the cell

Sister chromatids separate.

TelophaseSpindles & spindle fibers disintegrate

Chromosomes uncoil

Nuclear membrane forms

Two genetically identical daughter cells are formed.

Task: Make a mitosis ‘flip book’ detailing the stages of mitotic division. Notes available on pg. 53/54.

The mitotic index

Using a micrograph to estimate the ration between the number of cells in mitosis and the total number of observed cells.

Mitotic index = number of cells in mitosis

total number of cells

Cytokinesis

Is different in plants and animals.

Plants Animals

Vesicles move to the equator, fusing together forming a double plasma membrane layer across the cell.

Pectin & other substances are moved between this new layer, combining with cellulose to eventually form a new cell wall.

Plasma membrane pulled inwards

Proteins actin & myosin contract the plasma membrane, pinching the cell into two.

The Cell Cycle

Regulated by cyclins (proteins).

Cyclins bind to enzymes called cyclin-dependent kinases

Active kinase attach phosphate groups to other proteins which triggers more proteins to become active.

In humans there are four types of cyclin. See fig. 6, pg. 56

Tumours & cancer

Read detail on pg. 57, including the correlation between smoking and cancer.

Data based qu. Pg. 59.