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…

G1 (First Gap Period)Cell grows and increases in mass

Cell membrane (+ wall) are increasedNumber of organelles increaseChemical preparation for DNA Synthesis

(enzymes, deoxyribose sugars, nucleotide bases and phosphates synthesised)

Interphase

S phase (synthesis)Replication of DNA

Chromosomes held together by centromereIn animals centriole pairs duplicate

Interphase

G2 (Second gap phase)Cell builds up energy reservesIncreased 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

ProphaseChromosomes 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

MetaphaseSpindle 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

AnaphaseCentromeres divide

Sister chromatids separate and the chromosomes are pulled to the poles

Mitosis – anaphase cont…

Mitosis

TelophaseChromosomes 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…

Cytokinesis cont…

In plantsMembrane 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 www.biozone.co.uk/links.html

Cell biology – Mitosis / Meiosis – How cells divide

PostersCard sort (pictures / names / descriptions)Read Dart pg 9-14 and take notesUse ScholarAdvanced Higher Questions