1. Pages 80-81 Specification area 2.2
The Cell Cycle
The Cell Cycle
Pages 80-81
Specification area 2.2

2. Syllabus

3. Resources Text book Summary worksheet Link to APBI website
Cell Cycle Revision podcast on Kerboodle

4. Objectives Know the three stages of the cell cycle.
Be able to describe the main processes occurring during each stage of the cell cycle.
Explain how mitosis is controlled
Describe how cancer and its treatment relates to the cell cycle.

5. The Cell Cycle Know the three stages of the cell cycle
The cell cycle is divided into three major phases:
Interphase
The M phase or mitotic phase when Nuclear Division occurs
The C phase or cell division stage

6. The Cell Cycle
Describe the main processes occurring during each stage of the cell cycle
Cytoplasm divides and 2 ‘daughter’ cells separate
Nucleus Divides
Production of new proteins and organelles
DNA replicates

7. The Cell Cycle (Extension only)
INTERPHASE G1 G2 S
Cytokinesis
Interphase is divided
into G1, S and G2 phases
MITOSIS (M PHASE)

8. Interesting facts about Variations in duration of the Cell Cycle
G1 is the most variable
of all the phases
The rapidly dividing epithelial
cells lining the human intestine
remain in the G1 phase for
only about 2 hours G1 G2 S M
Slowly dividing liver cells
may take many months to
move through G1 to the
S phase
Some cells, such as nerve
and muscle cells never divide;
they may be considered to be
permanently in the G1 phase
and never enter the S phase

9. To do:-
Figure 2 Page 80 :
Copy Graph showing how Cell Mass and the mass of DNA changes during the cell cycle (lower graph) and add labels to show which stage of the cell cycle is on each part of the graph (5 minutes).

10. Interphase
MITOSIS
Interphase
MITOSIS G2 S G1 G1
Interphase

11. There are 75 cells in this field of view.
How do you think you might calculate the “MITOTIC INDEX”?
Hint: it is a proportion of cells in any stage of nuclear division

12. The Timing of the Cell Cycle
The different phases of the cell cycle last for different periods of time
An onion root slide was examined for the different stages of the cell cycle and
the number of cells in each phase was recorded
The percentage of cells in each stage was then calculated
The percentage of cells in each stage is used as a measure of the percentage of time that the cells spend in each phase of the cell cycle
Stage of Cell Cycle
Number of Cells
Cell % (approx)
Interphase
138 66
Prophase 56 27
Metaphase 6 3
Anaphase 2 1
Telophase 7
Total
209
100
Interphase is
the longest
stage of the
cell cycle
with anaphase
being the
shortest
3/100 * 72 = 2.16h OR
7/209 x 72 = 2.16h
If cell cycle takes 72 hours to complete, how long is Telophase?

13. Genetic Control of The Cell Cycle Out
The division of cells is a closely regulated process
Cell division is under genetic control, and it is known that there are
TWO specific genes which code for proteins that ‘switch on’ and
‘switch off’ the process
Cancer is a disease that results from uncontrolled cell divisions
When a MUTATION occurs in one of the genes that control Normal cell division, the resulting cells become transformed into cancer cells
Environmental factors such as cancer-causing agents (carcinogens like those in cigarette smoke), IONISING RADIATION (X-rays / UV / α ß ɣ), INCREASE THE RISK of these gene mutations

14. Click to goto link on causes of cancer

15. Scanning Electron Micrograph of Dividing Cancer Cells

16. Cancer: The Cell Cycle Out of Control
When a gene controlling division in a normal body cell mutates – the cell continues to divide uncontrolled to produce a clone of cells that form a tumour
normal
body cell
mutated
tumour
Uncontrolled
mitosis
mutation
Many such tumours are found to be BENIGN and do not spread from
their site of origin – they may nevertheless compress and damage adjacent tissues
Malignant, cancerous tumours are less stable and break apart so may spread from their site of origin
These tumours develop their own blood and lymph supply which can transport
malignant cells from the tumour to other sites in the body
malignant tumour
malignant cancer
cells carried to
other body sites
secondary
tumour
This is called
metastasis
these cells invade
other body regions
to form secondary
cancers

17. Describe how cancer and its treatment relates to the cell cycle.
To Do:-
Read the information about Cancer treatment.
Write down the effects of the TWO main types of drug used in Chemotherapy treatment
Copy the graph in figure 3 on p81
Give TWO features that are similar between the ‘normal’ and ‘cancer’ cell trends
What are the main DIFFERENCES between the effects of treatment on the normal and cancer cell numbers?

18. To Do:- answers Read the information about Cancer treatment.
Write down the effects of the TWO main types of drug used in Chemotherapy treatment
Prevent DNA replication during interphase of the cell cycle
Inhibit nuclear spindle formation so chromosomes cannot attach during metaphase of mitosis (thereby interfering with cell division)
Copy the graph in figure 3 on p81
Give TWO features that are similar between the ‘healthy’ and ‘cancer’ cell trends
Both cells types show declining numbers over time with repeated doses
In both cell types, there is a recovery period during after each dose has taken effect during which numbers remain stable before increasing again
What are the main DIFFERENCES between the effects of treatment on the healthy and cancer cell numbers?
The length of the recovery stage is shorter in healthy cells than in the cancer cells
The decrease in cancer cell numbers is greater after each dose than the decrease in healthy cell numbers

19. Homework
Answer summary questions and Question 5 in the application box on page 81.
Goto the following website and write the FIVE ways cancer can be caused
Also list all the different ways that cancer can currently be treated
Great link to cancer info

20. Outcomes I Know the stages of the cell cycle.
I can describe the main processes occurring during each stage of the cell cycle.
I can describe how cell division is controlled.
I am able to describe what cancer is and how it relates to the cell cycle.

21. Keywords Cell cycle Interphase Cytokinesis Cancer Chemotherapy drugs
Risk factors