Mitosis
Recap…
• The cell goes through growth phases.
• G1
Interphase
• S
• G2
• M phase and Cytokinesis
• Let’s talk about the M phase and Cytokinesis
• Cell growth occurs in
interphase
• During that time, DNA is
loosely organized- it looks a
bit like spaghetti.
• Remember: DNA is a doublestranded molecule made of
four different subunits called
nucleotides.
• A chromosome is one long
continuous thread of DNA
that consists of numerous
genes
centrioles
chromatin
nuclear
envelope
How does all the DNA fit inside
the nucleus of a cell?
• DNA wraps around proteins called histones that
help organize and condense it.
• This process looks similar to beads on a string.
• Parts of the histones interact with each other,
further compacting the DNA. At this stage – the
“spaghetti” stage – the combination of DNA and
proteins is called Chromatin.
• Recall that a chromosome is a strand of DNA, we
have 23
• During the S phase each chromosome is copied, so
we end up with 46 for the Mitosis phase
Continued….
• **DNA during the M-phase**
• As the cell progresses, chromatin further condenses,
it coils more and more tightly around organizing
proteins, finally forming small thick rods.
• Since the chromosome has already been copied during
the S phase, the chromosome looks similar to an “X”
in which the left and
right halves are two
identical DNA double
helixes
Continued……
• One half of a duplicated chromosome is called a
chromatid.
• Together, two identical chromatids are called sister
chromatids.
• Sister chromatids are held together at the
centromere, a region of condensed chromosome that
looks pinched.
• Lastly, at the ends of DNA molecules form structures
called telomeres, which are made of repeating
nucleotides that do not form genes.
• This prevents the ends of chromosomes from
accidentally attaching to each other or the loss of
genes.
Chromosomes
• The cells of every organism have a
certain number of chromosomes:
• Fruit flies: 8
• Humans: 46
• Carrots: 18
Cell Division
• Once the cell is completely prepped for
division, it enters the M phase.
• The M Phase is divided into 2 major
stages:
• Mitosis
• Cytokinesis
Mitosis
• Biologists have further divided mitosis
into four phases known as PMAT:
• Prophase
• Metaphase
• Anaphase
• Telophase
Prophase
spindle
• The nucleolus and
chromosomes
nuclear membrane
“break up” and temporarily disappear.
• Chromatin (spaghetti) condenses into tightly
coiled chromosomes, each consists of two
identical sister chromatids
• Centrosomes and Centrioles migrate to
opposite sides of the cell
• Organized microtubules called spindle fibers
grow from the centrioles and radiate toward
the center of the cell.
Prophase
Metaphase
• Only a few minutes long.
• Spindle fibers attach to the centromere
and align the chromosomes (sister
chromatids)
along the
cell equator
Metaphase
Anaphase
• Sister chromatids separate from each
other.
• The spindle fibers begin to shorten,
which pulls sister chromatids away from
each other and toward opposite sides of
the cell.
Anaphase
Telophase
• A complete set of identical chromosomes are
positioned at each pole of the cell.
• The nuclear envelope reforms around the
chromosomes
• Chromosomes begin to uncoil back
to
chromatin and the spindle fibers fall apart
Telophase
Cytokinesis
• This phase divides the cytoplasm into two cells and
completes a full stage of the cell cycle.
• Each cell is identical to each other
Cytokinesis
• In animal cells, the cell membrane is
pinched inward until the cytoplasm is
separated into nearly equal halves.
• The pinching creates a furrow or trench.
• In plants, a cell plate is formed in the
center of the cell and grows outward to
separate the two cells.
• A cell wall will eventually form on each
side of the cell plate.
Cytokinesis
Review – The Whole Process
Major Function of Mitosis
• In unicellular organisms, mitosis is
asexual reproduction. A new organism is
created.
• In multicellular organisms, mitosis
increases the number of cells to help
the organism grow and/or replace dying
cells.
Cell Cycle
includes
G1 phase
Interphase
M phase
(Mitosis)
is divided into
is divided into
S phase
G2 phase
Prophase
Metaphase
Anaphase
Telophase
Why do cells divide
rather than continuing
to grow indefinitely?
What are the three
limits to cell growth?
-The larger the cell becomes, the
more demands it places on the
DNA
-The cell has trouble moving
enough nutrients and wastes
across the cell membrane
1. Diffusion
2. DNA
3. Surface area to
volume ratio
What is cell division? The process by which 2
new cells are produced
from one cell.
What are the 4
phases of the cell
cycle?
1. G1 Phase
2. S Phase
3. G2 Phase
4. M Phase
Cell Growth – the cell
increases in size and
What happens during
synthesizes new proteins
the G1 Phase?
and organelles.
DNA Replication – a new
set of DNA is created
What happens during
from the original and
the S Phase?
proteins associated with
DNA are synthesized.
What happens during
the G2 phase?
Prep for Mitosis –
Organelles and molecules
required for cell division
are produced.
What happens during Mitosis and Cytokinesis
- Cell division occurs
the M phase?
In what form does
DNA –
genetic information take deoxyribonucleic acid
in eukaryotes?
During what phase does
cell growth occur?
What is chromatin?
What are the three parts
of Interphase?
Interphase
The granular material
made up of DNA bound
to protein.
G1, S, and G2 phases
What are sister
chromatids?
The original chromosome
joining with the copied
chromosome.
How are the two sides of
the chromatids joined
together?
centromere
What are the two parts of Mitosis and Cytokinesis
the M Phase?
What are the four phases
of Mitosis?
What happens during
Prophase?
- Prophase
- Metaphase
- Anaphase
- Telophase
-The nucleolus and nuclear membrane
“break up” and temporarily disappear.
- Centrioles duplicate and separate to
opposite sides of the cell.
-The mitotic spindle begin to form near
the centrioles.
What happens during
Metaphase?
-The chromosomes line up across the
center of the cell on an imaginary line
called the metaphase plate.
- Microtubules attach to the centromere
of each chromosome from both poles
of the spindle.
How are plants cells
different in prophase?
Plant cells do not have
centrioles but still form a
spindle to organize cell
division.
What happens during
Anaphase?
-The centromeres are broken and the
sister chromatids separate.
- Each sister chromatid is now called a
chromosome.
- The chromosomes continue to move
until they have separated into two groups
near the poles of the spindle.
What happens during
Telophase?
-Chromosomes begin to unwind back to
chromatin.
-The nuclear envelope reforms around the
chromosomes.
- a nucleolus becomes visible in each
daughter nucleus
-The spindle breaks apart.
What happens during
cytokinesis for animal
cells?
- The cell membrane is
pinched inward until the
cytoplasm is separated
into nearly equal halves.
What happens during
cytokinesis for plant
cells?
- A cell plate is formed in
the center of the cell and
grows outward to
separate the two cells.
What is the major
- mitosis is asexual
function of mitosis for reproduction so a new
unicellular organisms? organism is created.
Mitosis increases the number
What is the major
function of mitosis for of cells to help the organism
grow and/or replace dying
multi-cellular organisms?
cells.
What is this
phase and
what is
happening?
Interphase G1, S, G2, Cell growth,
and replication of DNA
and organelles.
What is this
phase and
what is
happening?
Prophase
-The nucleolus and nuclear membrane
“break up” and temporarily disappear.
- Centrioles duplicate and separate to
opposite sides of the cell.
-The mitotic spindle begin to form near
the centrioles.
What is this
phase and
what is
happening?
Metaphase
-The chromosomes line up across the
center of the cell on an imaginary line called
the metaphase plate.
- Microtubules attach to the centromere of
each chromosome from both poles of the
spindle.
What is this
phase and
what is
happening?
Anaphase
-The centromeres are broken and the sister
chromatids separate.
- Each sister chromatid is now called a
chromosome.
- The chromosomes continue to move until
they have separated into two groups near
the poles of the spindle.
What is this
phase and
what is
happening?
Telophase
-Chromosomes begin to unwind back to
chromatin.
-The nuclear envelope reforms around the
chromosomes.
- a nucleolus becomes visible in each daughter
nucleus
-The spindle breaks apart.
What are
stages of the
cell cycle?
1. G1 Phase
2. S Phase
3. G2 Phase
4. M Phase – Prophase,
Metaphase, Anaphase, Telophase