#13333 - Mitosis - Organisation of the Body

MITOSIS

-Cells undergo cell division- to replace cells that have been lost due to maturation/apoptosis

-cells also divide- inresponse to an increased work load

-seen by light microscope- labelled radioactive DNA precursors such as H3 Thymidine- recorded using autoradiographic methods

G0 phase

-most of the cells in this phase are differentiated- specific function

-to leave this phase requires growth factors

Progression through the cell cycle is dependent by cyclin dependent kinase which phosphorylates other substrates and promote cell divison

G1

-longest and most variable cell cycle phase- determines the length of the whole cycle

-requires continuous signals from growth factors

-large amount of growth- large amounts of RNA and protein synthesis

-restriction point at the end of G1 phase- determines whether cell can enter S phase- cell size, condition of the chromosomes, external environment or enter the G0 phase

-p53 stimulates the G1 phase to progress onto S phase

S

-all replication needed to create two cell occurs- DNA and organelles

-synthesis of DNA, replication of centrosomes

-centrosomes are key for cell division – each consists of two centiroles- barrels of 9 triplet microtubules

G2

-phase of chromosome packaging

-synthesis of proteins required for mitosis

-checkpoint determines if all the DNA has been replicated before mitosis and the environments condition are favourable

-mauration promoting factors stimulate progression

MITOSIS

-PROPHASE

-chromosomes first become visible- light microscopy, shorten and condense

-nuclear envelope and nucleolus disintegrate

-centrosome that has already divided goes to opposite pole of the cell

-METAPHASE

-microtubules radiate out from the centrosome into the nuclear area- nuclear spindle

-during metaphase the nuclear spindle is kept under constant tension, as a result of constant amount of tubulin molecules being lost from the negative end in the centromere, and then added to the positive end – through treadmelling the microtubules maintain a constant length

...