Cell division

Stages of Mitosis.

InterphaseProphaseMetaphaseAnaphaseTelophaseCytokinesis

Chromosomes uncoil and are not visible. DNA replicates as S phase

Nuclear membranes break down Centriole replicates and moves to opposite poles of cell Centrioles start to produce spindle fibres Chromosomes coil up tightly and are visible.

Spindle fibres hold each chromosome by the centrimere. Chromosomes align at the equator of the cell.

Centrimeres spilt Chromatids are pulled to the poles By spindle fibres contracting

New nuclear membranes form Spindle fibres disintergrate Chromosomes start to uncoil

Identical daughter cells are formed Resume normal function

Cell cycle.

G2 = Preparation for cell division, sythnesis of proteins and enzymes.

M = mitosis, the division of nuclear material

S = replication of DNA

G1 = Growth of cell, synthesis of more organelles and cytoplasm.

Meiosis

Vital to replace lost/damaged cells, or for growth of an organism.

Vital for reproduction, creates haploid cells (half parent cells chromosome number) so that at fertilisation the correct diploid number is restored in the zygote

Pair of Homologous Chromosomes that crossover - Swap allelles

Homologous chromosomes are separated into two cells

Sister chromatids are separated into 4 haploid cells. All daughter cells each with only one chromosome from original pair

DNA is replicated in preparation for division

The chromosomes from each pair are randomly separated into the daughter cells by Independent Assortment - the random separation of the homologous pairs into new cells with a mix of maternal and paternal alleles, this depends on how they align on the equator when seperated

Cancer.

Cancer is uncontrollable cell division that is too rapid. It leads to a mass of undifferentiated cells called a tumour.

There are two types of cancer -  Benign  Malignant - this is the one that spreads to cause secondary cancers.

We can treat them by targeting different stages of the cell cycle to prevent division. This targets rapidly dividing cells but can also harm healthy cells that divide quick such as hair follicles (hence hair loss)

At G1 we can prevent the synthesis of proteins and enzymes to enter the S phase, this prevents division

At

At the S stage we can use radio therapy to cause DNA to mutate when replicating to cause cell destruction as it can't repair the mutation, resulting in apoptosis - automatic cell death.

During mitosis we can prevent the formation of spindle fibres, this prevents replication by not being able to pass metaphase (cannot separate chromatids)

Stages of mitosis

Cell cycle

Stages of meiosis

Cancer