Transcript Cell Cycle2013/14

Unit 1: Cell & Molecular Biology
Cell Growth
&
Cell Cycle
Learning Intentions
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Interphase: G1, S and G2 phases
Mitosis: the M phase (4 stages)
Cytokinesis
Mitotic Index
Control of the cell cycle.
Abnormal cell division: cancer cells.
Four Phases of Cell Division
Cell growth and
synthesis of
organelles
Cell growth
and
synthesis of
organelles
Phase G1, S and G2
are collectively
known as interphase
DNA replication
M phase = Mitosis
(cell division)
Cell Division And The Cell Cycle
Cytokinesis is controlled by actin
fibres which split the cytoplasm in
two - stage 6
Stages of Mitosis
Stage
Description
Prophase
No distinct chromosome. Nuclear envelope intact
Prometaphase
Chromosome become visible. Nucleus breaks down
Metaphase
Chromosomes line up across the centre of cell
(metaphase plate)
Anaphase
Chromosomes divide into chromatids which are pulled to
opposite poles by spindle fibres. These are made of
microtubules and radiate from the centrosome.
Telophase
Daughter chromosomes ( chromatids) reach opposite
poles and begin to de-condense
Interphase
Follows the M phase and involves cell growth and
DNA replication. Made up of G1, S and G2
Mitosis – Prophase
The replicated chromosomes each consisting of two
closely associated sister chromatids condense
Outside the nucleus the mitotic spindle assembles between
the two centrosomes which have replicated and moved
apart.
Mitosis – Prometaphase
The nuclear envelope breaks down
Chromosomes attach to the spindle microtubules via
structures called kinetochores and move towards the equator
of the cell.
Mitosis – Metaphase
The chromosomes are moved to the equator by the spindle fibres
The kinetochores of all chromosomes align on the equator,
midway between the poles at a structure known as the metaphase
plate
Mitosis - Anaphase
The paired chromatids from each chromosome separate to form
two sister chromatids.
Daughter chromosomes are pulled to opposite poles by the
simultaneous shortening and lengthening of microtubules
Mitosis - Telophase
The two sets of daughter chromosomes arrive at the poles
A new nuclear envelope reassembles around each set
forming two separate daughter nuclei and marking the end of
Mitosis.
Nuclear division is controlled by
microtubules (tubulin protein) which form
the spindle fibres and move chromosomes to
opposite poles of the cell during mitosis.
Cytokinesis
• Once the cell completes M phase (mitosis)
the division of the cytoplasm produces 2
daughter cells this is known as
CYTOKINESIS.
• In animal cells the cytoplasm is divided into two by a
contractile ring of actin and myosin protein which pinches
in the cell to create two daughter cells.
• In plant cells a new cell membrane and cell wall are built
between the two daughter nuclei and cuts the cytoplasm in
half
Mitotic Index
• Mitosis duration and frequency varies greatly
between cell types.
• The Mitotic index calculates the percentage of
cells undergoing division in a given sample.
• Only cells goinf through M phase are counted (not
Interphase)
• This can be the first indication of cancerous cells
and a developing tumour.
Mitotic Index = Number of mitotic cells
Total number of cells
X 100