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 increased
Number of organelles increase
Chemical preparation for DNA Synthesis
(enzymes, deoxyribose sugars, nucleotide
bases and phosphates synthesised)
Interphase
S phase (synthesis)
Replication of DNA
Chromosomes held together by
centromere
In animals centriole pairs duplicate
Interphase
G2 (Second gap phase)
Cell builds up energy reserves
Increased 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
Prophase
Chromosomes 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
Metaphase
Spindle 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
Anaphase
Centromeres divide
Sister chromatids separate and the
chromosomes are pulled to the poles
Mitosis – anaphase cont…
Mitosis
Telophase
Chromosomes 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 plants
Membrane 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
Posters
Card sort (pictures / names / descriptions)
Read Dart pg 9-14 and take notes
Use Scholar
Advanced Higher Questions