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1.6 Cell division
Understanding:
- Mitosis is division of the nucleus into two
genetically identical daughter nuclei
- Chromosomes condense by supercoiling
during mitosis
- Cytokinesis occurs after mitosis and is
different in plant and animal cells
- Interphase is a very active phase of the cell
cycle with many processes occurring in the
nucleus and cytoplasm
- Cyclins are involved in the control of the
cell cycle
- Mutagens, oncogenes and metastasis are
involved in the development of primary and
secondary tumors
Applications:
- The correlation between smoking
and incidence of cancers
Nature of science:
- Serendipity and scientific
discoveries: the discovery of
cyclins was accidental
Nature of science:
- Identification of phases of mitosis
in cells viewed with a microscope
- Determination of a mitotic index
from a micrograph
Cell division
Mitosis: Division of the nucleus into two
genetically identical daughter nuclei
Mitosis
Needed for:
- Embryonic development
- Growth
- Tissue repair
- Asexual reproduction
- Four main stages (with one before, and then one
after!)
- Remember using PMAT
Before mitosis…
Interphase
Very active
Numbers of mitochondria in the cytoplasm
increase
In plant cells the chloroplasts also increase
Three phases – G1, S, G2
Interphase
Phase
G1
S
G2
What happens?
Before mitosis…
Your task
Complete the sheet to show the series of events
that happen during each stage of mitosis
Include diagrams
Once you have finished this, make sure you have
all notes (check through PPTs so far), then you
can revise for your test.
Please bring in the following on
Tuesday 3rd November
Prophase
1. Chromosomes become shorter and fatter by
coiling
2. Supercoiling so they become short enough
3. Nuclear membrane breaks down
4. Microtubules start to grow from each pole
Prophase
Metaphase
1. Chromosomes align on equator of cell
2. Microtubules continue to grow and attach to
centromeres on each chromatid
3. Microtubules put under tension to test if
they are attached correctly
Metaphase
Anaphase
1. Each centromere divides
2. Pairs of sister chromatids separate
3. Microtubules pull them towards the poles of
the cell
Anaphase
Telophase
1.
2.
3.
4.
5.
6.
Chromatids have reached the poles
Now called chromosomes
Microtubules disappear
Chromosomes pulled into a tight group
Nuclear membrane forms around them
Chromosomes uncoil and decondense and
nucleolus formed
Telophase
After mitosis…
Cytokinesis
1. Cell divides into two after telophase
Cytokinesis
Mitotic Index
Ratio between the number of cells in mitosis
compared to the total number of cells
Number of cells in mitosis
Total number of cells
MITOSIS DOES NOT INCLUDE INTERPHASE AND
CYTOKINESIS
How do you tell if the cell is in mitosis?
If you can see the chromosomes = in mitosis
Calculate the mitotic index
Mitotic Index
Number of cells in mitosis =
Total number of cells
MITOSIS DOES NOT INCLUDE INTERPHASE AND
CYTOKINESIS
Cancer = Higher mitotic index
(More cells in mitosis – higher rate of division)
Cyclins
Discovered by accident by Tim Hunt
Control the step by step program of the cell
cycle
Ensure everything is correct before moving to
the next stage
Cyclins
Bind to
enzymes
(cyclindependent
kinases)
Kinases
become
active and
attach
phosphate
groups to
other
proteins in
the cell
Proteins
become
active
Carry out
tasks in the
cell for
specific
stage of the
cell cycle
Four Cyclins
Different Cyclins have specific roles and phases
Cyclins must reach a threshold before the cell can
move to the next stage
Controls the cell cycle and ensures the cells do not
divide when they are not needed to
What if the cell cycle is not controlled
properly?
Research:
- Define the key terms and words
- What evidence is there that smoking and
cancer are related?
Tumor formation and cancer
Keyword
Benign tumor
Definition
What is the correlation between
smoking and death rate due to
cancer?
Malignant tumor
Carcinogen
Mutagen
Oncogene
Metastasis
Correlation
What evidence is there for this?
Tumor formation and cancer
Keyword
Benign tumor
Definition
What is the correlation between
smoking and death rate due to
cancer?
Malignant tumor
Carcinogen
Mutagen
Oncogene
Metastasis
Correlation
What evidence is there for this?