Mitosis
Part 1:
Chromosomes
I.
Chromosome structure- DNA can exist
in 2 different forms
A. Chromatin- DNA protein complex
that is not coiled (thin)
B. Chromosome- rod-shaped; DNA is
coiled tightly around proteins called
histones. Formed before cell division.
Each copy is called a chromatid.
FYI-The diagram
will help you see the
relationship in a cell.
1. Chromosomes
are found in the
nucleus
2. Chromosomes
are made of DNA
3. Sections of
chromosomes are
called genes
Eukaryotic Chromosomes
All eukaryotic cells store genetic
information in chromosomes
Most eukaryotes have between 10 and
50 chromosomes in their body cells
Human body cells have 46 chromosomes
or 23 identical pairs
4
Eukaryotic Chromosomes
Each chromosome is composed of a
single, tightly coiled DNA molecule
Chromosomes can’t be seen when
cells aren’t dividing and are called
chromatin
5
Compacting DNA into
Chromosomes
DNA is
tightly
coiled
around
proteins
called
histones
6
Chromosomes in Dividing Cells
Duplicated
chromosomes are
called
chromatids &
are held
together by the
centromere
Called Sister Chromatids**
7
**Karyotype**
A picture of the
chromosomes from
a human cell
arranged in pairs by
size
First 22 pairs are
called autosomes
Last pair are the
sex chromosomes
XX female or XY
male
8
Boy or Girl?
The Y Chromosome Decides
Y - Chromosome
X - Chromosome
9
II. Chromosome #’s-not related
to complexity of species
A. Each organism has a distinct number of
chromosomes, in humans, every cell
contains 46 chromosomes. Other
organisms have different numbers, for
instance, a dog has 78 chromosomes per
cell.
B. **There is no relationship between # of
chromosomes and speed of mitosis. It all
happens at the same rate.**
Chromosome #’s of various species
Organism
# of Chromosomes
Ant
2
Mosquito
6
Bearded Dragon
32
Cat
38
Pig
38
Axolotl
28
Dog
78
Hedgehog
90
Carp (highest animal)
104
Corn
20
Algae
148
Adder Fern (highest plant)
1260
Aulacantha (Protist)
1600
C. Sex Cells - also known as gametes.
These cells contain half the number of
chromosomes as body cells and are
called HAPLOID. (for us = 23)
This is referred to as the N number.
So, our N number is 23.
•If you have XX sex chromosomes - you are
female.
•If you have XY sex chromosomes - you are
male.
•During fertilization, sperm cells will either
contain an X or a Y chromosome (in addition
to 22 other chromosomes - total of 23). If a
sperm containing an X chromosome fertilizes
an egg, the offspring will be female. If a sperm
cell containing a Y chromosome fertilizes an
egg, the offspring will be male.
D. Autosomes -all the other
chromosomes; every cell of an organism
has 2 copies of each autosome (2N). (N is
23, so 2N = 46)
This is our Diploid number (2N).
-We receive one copy from each parent,
called homologous chromosomes- the same
size and shape, and they carry genes for
the same traits.
Homologous chromosomes, 2 pair
Cell Division- Prokaryotes
A. Cell Division in
Prokaryotes.
1. Binary Fissionthe division of a
prokaryote into 2
identical cells.
2. Considered
asexual (one
Remember- prokaryotes
parent)
are bacteria!
B. 3 General Stages
1. Chromosome makes
a copy of itself,
attached to the
inside of the cell
membrane.
2. Cell doubles in size
3. Cell wall forms
between the 2
chromosomes and
the cell divides,
forming 2 equal
cells.
Prokaryotes vs. Eukaryotes
Prokaryotes
Eukaryotes
Bacteria
All other organisms
Binary Fission
Mitosis
In all bacteria
All cells but sex cells
Have circular DNA
Have chromosomes
Replicates at 500 bp/min.
Replicates at 50 bp/min.
Produces identical organisms
Produces identical cells
What is Mitosis?
• The splitting or dividing of the nucleus
• **Produces two genetically identical cells
from one cell.
• **Form of asexual reproduction, used for
growth, repair, and reproduction.
• Occurs only in certain types of cells (body
cells except the sex cells), and in singlecelled protists.
B. The Cell Cycle- Stages
(Use your WS for this
part)
-not considered part of
mitosis- is time
between divisions.
1. Interphase (longest
part of the cell cycle)
• G1 (Growth 1)
• S (Synthesis) - DNA
copies
• G2 (Growth 2) - cell
prepares for division,
organelles double
Interphase
• Cells spend most of its time in this
phase
• Cells are growing
• DNA has to be replicated (all 2
meters of it)
• Proteins are being produced
• 90% of all cells are in this phase
• Three phases:
G1, S, and G2
The Cell Cycle: G1 phase
• Growth phase 1:
proteins are made, cell
grows to normal size.
• If checkpoint here
passed, cell will
complete division
• Some cells, like nerve
cells, stay in this
phase forever.
The Cell Cycle: S phase
• All nuclear DNA is
replicated
• Chromosome
number doubles
• Checkpoint: does
cell have all its
chromosomes
doubled properly?
The Cell Cycle: G2 phase
• Cell volume
increases
• Centrioles with
their microtubules
form (centrosome)
• Organelles double.
• Checkpoint: is cell
large enough to
divide?
Photo of Interphase
Whitefish blastula cells
C. Mitosis Phases
This animation shows
the process of
mitosis.
1. Prophase
• DNA shortens and
coils into
chromosomes;
• nucleolus and nuclear
membrane break down
and disappear;
• centrioles appear and
move towards
opposite poles
• Spindle fibers appear
and attach to
centromere.
Cells Alive Mitosis
Animation (click
here)
Early Prophase Photo
2. Metaphase
• Chromosome pairs
line up in the
center by the
centromere.
• Move along spindle
fibers.
Metaphase Photo
3. Anaphase
• Chromosomes split
at centromere.
• Chromosomes move
to opposite poles.
Anaphase Photo
4. Telophase
• DNA lengthens and
disappears.
• nucleolus and
nuclear membrane
reappear.
• centrioles and
spindle fibers
disappear.
• Cell Splits (called
cytokinesis),
forming 2 equal
cells.
Telophase Photo
Cytokinesis
• The process by which the cytoplasm
divides and one cell becomes two individual
cells. The process is different in plants
and animals:
•
Animal cells – cell membrane pinches in and
•
Plant cells- vesicles from the Golgi apparatus
fuse at the midline forming a cell plate, which
separates the 2 cells = cleavage furrow
will become the cell wall.
Cleavage Furrow
Animation of cell plate forming
Now, name the phases as they
occur in the animation.