Mitosis
PAG 1
Drawing stages of mitosis
Mitosis and Cell Cycle
Learning Objectives
• - Collection and
presentation of data:
• • Produce a root tip squash;
• • Use a light microscope to
produce annotated
drawings of the stages of
mitosis.
Success Criteria
• List purpose of mitosis
• Carry out a qualitative
Practical Assessment
Practice
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)
Mitosis (M)
Process by which a nucleus divides into
two – each with an identical set of
chromosomes – the nuclei are genetically
identical
Four phases – prophase, metaphase,
anaphase, and telophase
Two daughter cells – genetically identical
Followed by cytokinesis – division of
the cell into two genetically identical
daughter cells
The life cycle of a cell
Interphase can be
divided into 3 phases
(ITS NOT RESTING!)
• G1 – cell growth,
duplication of
organelles
• S – DNA replication
and chromosome
duplication
• G2 – cell growth and
preparation for mitosis
The Cell Cycle
G2 - Second growth
phase - short
Short gap before mitosis
(cell division)
Cell continues to
increase in size, energy
stores increased.
Cytoskeleton of cell
breaks down and the
protein microtubule
components begin to
reassemble into spindle
fibres – required for cell
division. DNA checked
for errors.
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 = 40
Cytokinesis – cell
divides into two
DNA content = 20
G1 - First growth phase –
longest phase
Protein synthesis – cell “grows”
Organelles replicate
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
Interphase – S phase
• Before mitosis can occur 2 copies of each
chromosome are needed.
• During interphase the chromosomes which
initially consist of a single DNA molecule are
duplicated.
•The new chromosome is made of two
identical structures called chromatids
•Each chromatids contains one DNA
molecule
•Chromatids are held together by a
region called the ‘centromere’
•DNA is made up of a series of genes
Mitosis
During mitosis, the cell’s DNA is copied into each of the two
daughter cells. In multicellular organisms, mitosis provides new
cells for growth and tissue repair.
In eukaryotes, it can also be a form of asexual reproduction. This
most commonly occurs in single-celled organisms, such as yeast.
•
•
Can be split into four stages:
Constuct a Table: three columns
Stage, Details, picture
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase.
• Mitosis animation
Before a cell divides, its chromosomes are copied exactly in INTERPHASE.
This process is called replication; ATP is synthesised – provides energy for
cell division; organelles are replicated and proteins are made
PROPHASE
The DNA of each chromosome is copied to form two chromatids (“sister”
chromosomes); chromosomes condense – becoming shorter and fatter –
visible under LM; nuclear envelope breaks down; chromosomes lie freely in
cytoplasm; centrioles move to opposite ends of the cell, forming protein
(tubulin) fibres across it called a spindle – fibres extend to the equator of the
cell
METAPHASE
Chromosomes line up at the equator; the spindle fibres from each pole
become attached to the centromere of the chromosomes
ANAPHASE
The spindle fibres contract; the centromeres are split and the pairs of sister
chromatids are separated and dragged to opposite poles assuming a “V”
shape – the centromeres lead; a complete set of chromosomes is therefore
found at each pole; energy (ATP) is required
TELOPHASE
Chromatids reach their respective poles and uncoil – become thin and long
again – now called chromosomes again – no longer visible under LM; spindle
fibres break down; nuclear envelope forms around each group of
chromosomes – forming two nuclei; cytokinesis follows – cytoplasm divides
and a plasma membrane forms two form two individual cells; cell enters
interphase once again
• The chromosomes shorten and
thicken by coiling (supercoiling)
• The nuclear membrane breaks
down at the end of prophase
• The other structures important
for mitosis are also forming (i.e.
the centrioles or microtubule
organising centre MTOC).
Microtubules grow from the MTOC at the poles of the cell to the
chromosomes. They form a spindle shape. (Mitotic spindle)
•
The chromosomes are lined up along
the cell's equator .
• Spindle microtubules from each pole
are attached to each centromere on
opposite sides.
• The centromeres divide and the
sister chromatids have become
chromosomes.
• The chromosomes are pulled along
the microtubules toward opposite
poles of the cell.
• The chromosome have
migrated to the poles.
• The nuclear membrane
reforms.
• The mitotic structures
breakdown.
• The chromosomes uncoil.
• The plasma
membrane of the
cell pinches down
along the equator
creating two
separate cells. At
this time, the
chromosomes
become indistinct
(as they are during
Interphase).
Biological significance
of mitosis?
The significance of mitosis is its ability to produce daughter
cells which are exactly the same as the parent cell. It is
important for three reasons…
• If a tissue wants to get bigger by growth it needs new cells
that are identical to the existing ones.
• Damaged cells have to be replaced by exact copies of the
organism so that it repairs the tissues to their former
condition.
• It is the basis of asexual reproduction.
Task - Demonstrate use of a light microscope (working towards PAG1)
Examining cells under the microscope
• Examine the
prepared
slides and
draw
accurately
what you see!
• Do this in your
lab book after
you have
checked your
understanding
on the next
slide!
Just before you
draw: Check your
understanding.
Shading present
Label lines not touching correct place (cell wall)
Label lines not parallel with top of page
No magnification given