What is the difference between mitosis and meiosis?
When will each occur?
Objectives
Outcomes
3: Identify stages of the cell cycle.
5: Describe the stages of the cell
cycle.
7: Explain the consequences of the
cell cycle not being properly
controlled.
Key terms: cell cycle, interphase, mitosis, cytokinesis.
The Cell Cycle, Mitosis, and Meiosis
New cells can only be made when existing cells divide. All cells have the ability to divide – but
some cells lose this ability.
Intestinal epithelial lining - replaced every five days by cell division
Liver cells - divide only to repair damage, and then stop dividing
Bone marrow cells - divide repeatedly to produce red and white blood cells
Meristem cells (tips of roots and shoots) – divide to produce new
growth
Cambium cells (plants) – divide to form vascular tissue (xylem and phloem)
These are relatively unspecialised cells. Specialised cells often go through the cell cycle only
once - the nerve cells, once formed cannot divide again.
In eukaryotic cells, there are two types of cell division – mitosis and meiosis. Mitosis is used to
produce new cells for growth and repair. Meiosis is used in the formation of gametes only.
In prokaryotes (bacteria), cell division does not involve mitosis or meiosis – bacteria reproduce
asexually, by a type of cell division termed by binary fission. Yeasts reproduce asexually by
budding.
The cell cycle is the process that all body cells from multicellular organisms use to grow and
divide. The cell cycle starts when a cell has been produced by cell division and ends with the
cell dividing to produce two identical cells.
The cell cycle describes the sequence of cell growth and cell division.
It includes:
Interphase
cell growth
synthesis of organelles
DNA copying and checking of genetic information
Mitosis
chromosomes divide
Cytokinesis
cytoplasm divided between the daughter cells
Key terms: cell cycle, interphase, mitosis, cytokinesis.
The cell cycle describes the events during one complete cycle of
division, they are represented in the chart:
Key terms: cell cycle, interphase, mitosis, cytokinesis.
Key terms: cell cycle, interphase, mitosis, cytokinesis.
INTERPHASE
G1
Period of cell growth; cell prepares cell for
cell division (mitosis); genetic material (DNA)
is copied and checked for errors – prevents
mutations being passed on
No apparent activity
S phase
CELL
CYCLE
G2
New organelles and proteins are made
Divided into three phases (G1, S, and G2
phase)
MITOSIS (M)
Process by which a nucleus divides into two –
each with an identical set of chromosomes –
the nuclei are genetically identical
Mitosis (M)
Four phases – prophase, metaphase,
anaphase, and telophase
Followed by cytokinesis – division of the cell
into two genetically identical daughter cells
Two daughter cells – genetically identical
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.
Bacterial cells complete the cycle every 20 minutes. Muscle cells never complete the cycle –
“terminal differentiation”
Uncontrolled and repeated cell division by mitosis results in cancer (tumours)
The Cell Cycle
Cytokinesis – cell
divides into two
DNA content = normal
G2 - Second growth phase
- short
Short gap before mitosis
(cell division)
Cytoskeleton of cell breaks
down and the protein
microtubule components
begin to reassemble into
spindle fibres – required
for cell division
DNA content = 40
S - Replication phase DNA
replication – this must
occur if mitosis is to take
place
The cell enters this phase
only if cell division is to
follow
DNA content = double
G1 - First growth phase – longest
phase
Protein synthesis – cell “grows”
Most organelles produced
Volume of cytoplasm increases
Cell differentiation (switching on
or off of genes)
Length depends on internal and
external factors
If cell is not going to divide again
it remains in this phase
DNA content = 20 (arbitary)
G1 + S + G2 = INTERPHASE
No apparent observable activity
Task
Outcomes
Create a poster outlining the cell
cycle. Leave some space for
when we fully look at mitosis in
the next lesson.
3: Identify stages of the cell cycle.
5: Describe the stages of the cell
cycle.
7: Explain the consequences of the
cell cycle not being properly
controlled.
Key terms: cell cycle, interphase, mitosis, cytokinesis.
What happens when the cell
cycle is not controlled:
Cancer
Outcomes
3: Identify stages of the cell cycle.
5: Describe the stages of the cell
cycle.
7: Explain the consequences of the
cell cycle not being properly
controlled.
Key terms: cell cycle, interphase, mitosis, cytokinesis.
Key terms: cell cycle, interphase, mitosis, cytokinesis.