Cell Division – The Cell Cycle
What are mitosis and meiosis and
what happens in them?
Starter:
What can you remember about mitosis and meiosis.
Summarise the 2 processes.
Success Criteria
• Recap Mitosis and Meiosis from GCSE
Describe the main stages of mitosis (with the aid of
diagrams and photographs) behaviour of the
chromosomes, nuclear envelope, cell membrane
and centrioles.
State that mitosis only occupies a small percentage
of the cell cycle and that the remaining percentage
includes the copying and checking of genetic
information.
• https://www.tes.co.uk/teachingresource/Cell-Cycle-Mitosis-and-Meiosis6260954/
• Skip from 7 – 11minutes
The Cell Cycle
Eukaryotic cells have a well- defined cell cycle of growth and division (mitosis). The
length of the cycle varies (from minutes to hours, or , longer) ending with mitosis.
Each phase of the cycle involves specific activities, and varies in length from one
organism to another.
The cell cycle can be divided into stages:
G1 (“growth phase” 1) - Cells prepare for DNA replication
S (“synthesis”) - DNA replication occurs
G2 (“growth phase” 2)- Short gap before mitosis
M Mitosis (relatively short)
Affected by availability of nutrients.
Between each stage the cell “checks” to see if it is OK to proceed to the next stage.
“Proof-reading” enzymes check the copied chromosomes for mistakes (mutations) –
the cell may kill itself (undergo “suicide”) if harmful mutations are – a process known
as apoptosis.
This is the cell cycle.
G1 = production of
proteins and new
organelles.
S = Synthesis of new
DNA
G2 = growth of the cell.
M = Mitosis and cell
division (nuclear
division and
cytokinesis)
I = interphase = G1 , S
and G2
INTERPHASE
CELL
CYCLE
G1
Period of cell growth; cell
prepares cell for cell division
(mitosis); genetic material (DNA)
is copied and checked for errors
S phase
New organelles and proteins are
made
G2
MITOSIS (M)
Mitosis (M)
Process by which a nucleus
divides into two – each with an
identical set of chromosomes –
Four phases – prophase,
metaphase, anaphase, and
telophase
Followed by cytokinesis –
Two daughter cells – genetically identical
Cytokinesis:
Division of the cell into 2
daughter cells
May occur during or after
telophase
The whole cell splits to form
2 new cells each one
containing a full set of
chromosomes identical to
the parent cell.
Each daughter cell is now
capable of doing everything
the parent cell can.
TASK – use
the books to
help you
Stage
G1
S
G2
What happens
Stage
G1
What happens
Active stage, growing, proteins made, organelles
replicate
S
DNA replicates and 2 sister chromatids form from
each chromosome
Growth till mitosis: Mitochondria divide,
chloroplasts divide in plants
G2
Mitosis
What do the following terms mean?
Centromere
Centriole
Chromosome
Histone
Chromatin
Allele
homologous
2n
Chromosome from
father
DIPLOID parent cell with
one pair of homologous
chromosomes.
Chromatin super coils and
is now visible.
Chromosome from mother
Each chromosome
duplicates (DNA synthesis)
to form 2 pairs of
chromatids held together
by a centromere.
The copies are called
sister chromatids.
Diploid
daughter
cells
genetically
identical to
parent cell
Mitosis – what do you know
• Complete the card sort and answer the
following questions.
1) What happens to the DNA in mitosis?
2) What is the name of the cells produced in
mitosis?
Mitosis
At GCSE:
1) Parent cell
2) Chromosomes make
identical copies of themselves
3) They line up along the
centre
they move apart
4) Two daughter cells form
with identical chromosomes
to the parent cell
Meiosis
What are the main differences between the genetic
material of eukaryotes and prokaryotes?
DNA and histones
Each human chromosomes contains 1 very long DNA molecule
which if unravelled would measure 4.8cm (& this is just ONE
chromosomes) therefore there is a packaging problem!
So…Chromosomal DNA is
folded and tightly bound to
proteins called histones.
DNA+histones=chromatin
Apart from sex chromosomes, both
chromosomes in a pair contain the
same genes. They are
HOMOLOGOUS pairs of
chromosomes.
Although they contain the same
genes e.g. hair colour, they may be
different versions of the same gene
(alleles) e.g. blue/brown hair.
Humans= 23 pairs of
chromosomes
E.g. one chromosome may have
one allele for blue eyes and the
other chromosome may have the
allele for brown eyes.
2n
Chromosome from
father
DIPLOID parent cell with
one pair of homologous
chromosomes.
Chromatin super coils and
is now visible.
Chromosome from mother
Each chromosome
duplicates (DNA synthesis)
to form 2 pairs of
chromatids held together
by a centromere.
The copies are called
sister chromatids.
Diploid
daughter
cells
genetically
identical to
parent cell
Why does the chromatin super coil? 2
marks
• The chromatin super coils in order to make it
thicker and more sturdy.
• This means it can be moved around without
being damaged.
FACT : super coiled chromatin is 500nm thick
compared to non super coiled = 30nm thick.
Why does the chromatin super coil? 2
marks
• The chromatin super coils in order to make it
thicker and more sturdy.
• This means it can be moved around without
being damaged.
FACT : super coiled chromatin is 500nm thick
compared to non super coiled = 30nm thick.
Mitosis in more detail.
• http://www.biology.arizona.edu/cell_bio/activ
ities/cell_cycle/cell_cycle.html
Mitosis in brief:
4 phases: PMAT (In total IPMAT)
Prophase-replicated chromosomes
supercoil (thicken & shorten).
Metaphase-Replicated chromosomes line
up down the middle of the cell
Anaphase-The replicas of the
chromosomes are pulled apart from each
other towards opposite poles of the cell
Telophase-two new nuclei are formed
MITOSIS
You need to know the different stages of
mitosis in more detail.
Using the textbook p30-31 for further info
or the revision guide page 20.