Transcript Control of Cell Cycle

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 Control

There are three checkpoints in the cell cycle.

Where do you think these are and why?
CK
Control of Cell Cycle
 G1
Checkpoint
 End
of the G1 phase
 Cell size is assessed
 If large enough the cell enters S-phase
 The
cell is usually pushed past this point by
signals (growth factors) from outside the
cell
Control of Cell Cycle – G1 cont…
 If
conditions are met
 DNA
replication enzymes called polymerases are
transcribed to allow S-phase to begin
 If
conditions are not met
 Cells
don’t divide and remain in G0 (roughly
equivalent to G1)
 Many mature cells e.g. nerve cells, skeletal muscle
cells, RBCs don’t divide
Control of Cell Cycle

G2 Checkpoint
 DNA replication success is monitored
 If replication is successful
 DNA
polymerase enzymes are deactivated
 Metaphase enzymes are activated (see MPF)
 If
replication is unsuccessful
 Any
cell with unreplicated or damaged DNA that
can’t be repaired is destroyed (apoptosis = cell
suicide)
Control of Cell Cycle - MPF

Mitosis (maturation) Promoting Factor (MPF)
 Promotes transition of G2 to M phase
 Acts as a catalyst for the conversion of
metaphase enzymes from an inactive to an
active state (by phosphorylation)
Control of the Cell Cycle

M Checkpoint
 Occurs during metaphase
 Checks
the spindle has assembled properly
 All chromosomes are attached properly (by the
kinetochores)
 If
conditions are met
 Metaphase enzymes are deactivated
 Anaphase enzymes are activated
Abnormal Cell Division: Cancer

What do you already know about cancer and its
causes?
Abnormal Cell Division: Cancer

Introduction
Cancer cells by-pass normal cell control
mechanisms. As a result they divide
uncontrollably to form lumps of tissue
(tumours) that no longer carry out their
function.
Mutation to Proliferation Genes

Normal proliferation genes are called Protooncogenes
 During normal cell division proto-oncogenes
code for proteins (e.g. growth factors) that
promote cell division
Mutation to Proliferation Genes…

Mutated Proliferation genes are called
oncogenes
 Oncogenes
act to produce cells that are not
required.
E.g.
 Produce
a protein which triggers a response in
the cell as if growth factors are present
 Over production of growth factors
Mutation to Proliferation Genes…
 Oncogenes
 Only
are dominant
1 gene in the pair of alleles needs to mutate
for it to have an effect.
 Mutations in several different genes are usually
required for cancer to develop.
Mutation to Anti-proliferation genes


(AKA Tumour
Suppressor Genes)
Normal Antiproliferation Genes
Switch off cell
division when
something goes
wrong
 If the cell is damaged
beyond repair
apoptosis occurs

Mutation to Anti-proliferation
Genes..

Mutations to Anti-proliferation Genes
 Cause
the cell to continue dividing when
faulty
 E.g.
p53 is a protein produced by a antiproliferation gene. It binds to damaged DNA
stopping cell division until it is repaired. A
mutation to this gene results in a faulty protein
and cell division with faulty DNA
Mutation to Anti-proliferation
Genes..
 Mutations
to anti-proliferation genes are
recessive
 Both
alleles of the gene are required to be
mutated for mutation to take affect
 Mutations in several different genes are usually
required for cancer to develop
Learning Activities





Write a brochure or a story to explain what
cancer is to a young child (assume they know
about cells).
Genetic Origins of Cancer worksheet
Advanced Higher Questions
Read Dart pg 14-17
Scholar