Download Cell cycle and Mitosis

Chromosomes
Learning Objectives
You will have been successful if by the end of the lesson you
can demonstrate and apply your knowledge and
understanding of
• The significance of mitosis in life cycles
To include growth, tissue repair and asexual reproduction in plants,
animals and fungi.
• Cell cycle
To include the processes taking place during interphase (G1, S and
G2), mitosis and cytokinesis, leading to genetically identical cells.
• How the cell cycle is regulated
To include an outline of the use of checkpoints to control the cycle
The beginning…….
Ovum
Zygote
Its nucleus
contains 23
chromosomes
+
Sperm
Its nucleus
contains 23
chromosomes
The nucleus from the
sperm fuses with the
ovum nucleus – now
there are 46
chromosomes in the
cell (23 pairs)
Millions of cells will
be produced from this
beginning
Karyotypes
The chromosomes from a dividing cell can be photographed and
organised into the pairs – one from the mother and one from the
father
Each pair has a characteristic size, shape and banding pattern
(except for the sex chromosomes where the X and Y
chromosomes are different)
Autosomes
22 pairs
Karyotype
from a
female
Make a
karyotype
Try it
yourself
Heterosomes
1 pair
Homologous chromosomes
• The 22 pairs of autosomes are known as homologous
chromosomes – they have the same genes in the same places
Visible chromosomes?
• When we can see distinct chromosomes its because the DNA molecules
are tightly coiled
About 3% of one of the DNA
molecules of one of the 46
chromosomes ! Packing this
amount into the nucleus takes
some doing……
The solution…..
• Coil the DNA strand
around histone proteins
• Keep on coiling……
DNA coiling
animation
Link the terms with the correct definition
e.g. B2
A
centriole
B
nucleolus
C
heterosomes
D
histone
1
Organelle in animal cells which
produces the spindle
2
Chromosome pairs which are
homologous
3
Cell(s) produced as a result of
fertilisation
4
Dark staining area within the
nucleus
The chromosome pair which
determines gender
E
zygote
5
F
karyotype
6
Picture of the chromosomes from a
cell
G
homologous
7
H
autosomes
Chromosomes with the same
genes in the same location
8
Protein around which DNA strands
coil
Significance of Mitosis
Mitosis is the division of the
nucleus
• Daughter cells are identical to the
parent cell
• Mitosis occurs during
• Growth
• Repair of tissues
• Asexual reproduction
Prokaryotes use a form of cell
division called binary fission
because they don’t have a
nucleus and therefore cannot
carry out mitosis
Why the X-shape ?
• Use your materials to create a “cell” with 2
homologous pairs, 4 mitochondria (pasta) and 6
ribosomes (beans). Now create two identical cells.
Homologous
pair 1
Maternal
Paternal
chromosomes
chromosomes
Homologous
pair 2
How does the cell produce the extra DNA?
What else would the cell have to do…..?
Can you explain this diagram?
Chromatids
• Each molecule of DNA in the nucleus replicates to produce 2 identical
strands
• The strands are called chromatids
• They remain joined together at the centromere
So…before the cell can begin to divide
• DNA molecules must replicate
• And then coil and coil again and again…
• The number of organelles needs to increase
Cell Cycle
McGraw Hill
Animation
Interphase
G1 – protein synthesis
and growth
S – replication of DNA
G2 – organelles divide,
DNA condenses
Mitosis
Nuclear division –
4 stages
Cytokinesis
Cell divides into two
Animation re p53 and DNA proof reading
And lung cancer
Nobel Prize game re cell cycle and checkpoints
Cell Cycle Checkpoints
Cell cycle
and
Mitosis
(Cells Alive)
These control the cell cycle.
Ensure that each stage is
completed properly before entering
the next stage.
G1 Checkpoint
cell size
(S Checkpoint
DNA synthesis complete)
G2 Checkpoint
Cell size
DNA replication
DNA damage
M checkpoint
Spindle assembly
Control of Cell Cycle
G0 is where the cell
leaves the cell cycle.
• Differentiation
• DNA damaged
• Scenescence
Page 122 OCR
Textbook
CDK enzymes control the checkpoints
A group of enzymes called
kinases move the cell onto the
next stage of the cell cycle
Kinases bind to proteins called
cyclins forming a CDK complex.
(cyclin dependent kinase
complex)
They phosphorylate a checkpoint
protein which activates it and
allows the cell cycle to move on.
After they have done their job the
checkpoint proteins are broken down
by other enzymes. Cell moves forward
through cell cycle
Cancer can develop if there is damage in the checkpoints leading to uncontrolled cell
division. Eg Over expression of the cyclin gene =too many cyclins being produced.
Some cancer drugs are inhibitors of these CDK complexes.
The Cell Cycle
Interphase, Nuclear division,
Cell division
Mitosis
Animation
(J Kyrk)
McGraw Hill
Animation
narrated
SciCast
Homemade
Animation
Learning Objectives
You will have been successful if by the end of the lesson you
can demonstrate and apply your knowledge and
understanding of
• the main stages of mitosis
To include the changes in the nuclear envelope, chromosomes,
chromatids, centromere, centrioles, spindle fibres and cell
membrane.
• sections of plant tissue showing the cell cycle and stages
of mitosis
Interphase
Mitosis – nuclear division
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Images of mitosis
in root tip
Interphase
Three parts –
G1 – Protein synthesis
S – Replication and checking
of DNA
G2 - Organelles divide
DNA condenses (coils)
Cell Division consists of mitosis which is divided into stages
and cytokinesis where the cells physically separate into 2
Prophase
Remember microtubules?
Mitosis in Sand Dollar –
video of spindle fibres
Metaphase
equator
Anaphase
Telophase
The chromatids are at the
poles
They are now called
chromosomes
Cytokinesis
In plant cells
In animal cells
Golgi apparatus
sends vesicles to
the middle of the
cell and they
fuse.
The cytoskeleton pulls the
cell surface membrane in
until it fuses
Cell wall then forms.
I
P
M
T
A
Interphase and nuclear division – in
Video of mitosis
photomicrographs
sequencing
Mass of DNA per nucleus / arbitrary units
Can you predict the shape?
Complete cell cycle takes
24 hours
2
1
Start of
G1
12
24
36
48
Time / hours
You should make sure you have the following materials:
micrographs
diagrams
text labels
text books
Now arrange the images and labels onto your A4 sheet to
create a record of
Interphase and Mitosis….
Then….collect the long answer practice questions
‘GCSE’ mitosis video
Stem Cells
The Nature of
Stem Cells
Undifferentiated cells which can still divide
New cells can then differentiate. This is when they specialise for one role.
Hierarchy of Stem Cells
Can divide and
differentiate into any
cell type and whole
organisms
Can divide to form all
cell types but not
whole organisms
multipotent
Stem Cell Interactive
Degrees of Stem cell division (potency)
Totipotent
Can divide and differentiate into any cell type.
Found in very early embryos
Create whole organisms
Pluripotent
Can divide to form all tissue types
Can’t divide to from a whole organism
Multipotent
Can divide but tend to become one of a class of cells.
Bone marrow contains stem cells than can divide to
form different blood cells
Sources of Stem Cells
•Plants
The cambium in the vascular tissue
can divide and form new phloem and
xylem
Sources of Stem Cells
Animals
Embryo/foetal cells which start off totipotent and become pluripotent
Adult stem cells which are multipotent eg bone marrow.
Umbilical cords.
Could store these for future use by the individual
Stem Cell Treatments
Page 140-141
Make brief notes on potential uses.
Ethical issues in the use of stem cells
arguments for and against their use
Horizon
Blood Stem Cells
Bang goes the theory
stem cell treatments
Root tip squash
Safety
Hazard
Precaution
General
Stand, tie hair back
keep walkways clear
Care
Care
Clear spills
Wear safety goggles
Glass ware
Hot plate
1M HCl
Acetic orcein
stain
Orcein Hazcard
Remedial measures
Inform staff
Rinse under cold water
Rinse skin, inform staff
HCl Hazcard
Root tip squash
• What you are going to do
Squash a root tip!
 Why
a root tip?
Plant cells only divide in particular parts
of the plant. The root tip is one such
location, they are termed meristems