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Chromosomes & Cell Cycle
What the heck is a Chromosome
anyway?
Chromosomes
- Chromosomes are tightly coiled rod like
structures
- They consists of DNA & proteins.
DNA itself is wound up into a thin fiber which
is wrapped around proteins called “Histones”
The Histone & DNA structure forms a
beadlike structure known as a “Nucleosome”
The Nucleosomes pack together to form a
thick fiber which starts to coil.
These coils wind up even more and become
“Supercoils”
The super coils are wound up to form a larger
structure that is called a “Chomosome”
Only during cell division are these
chromosomes ever visible.
Chromosomes
What part of the chromosomes
should I know?
Centromere – holds together
the two chromatids
Sister Chromatids –
genetic material from each
parent
This is 1
chromosome
This is a
duplicated
copy
At one period of time scientists thought that
cells were constantly dividing and replacing old
and dead cells.
During the time they were not duplicating and
just growing, scientists gave this term a name
called:
“Interphase” – which means “resting phase”
Eventually scientists found that a lot happens
between the resting phases. This is now what
we call the “Cell Cycle”
CELL CYCLE
M phase
We start along this line and cover this section.
This section is known as the G1 phase
- This is where cells do
most of their growing
- Cells synthesize new
proteins and organelles.
G1 phase
M phase
After all the thngs in G1 are done, the cell
then moves to the next phase in it’s life called
the “S phase”
- Chromosomes are
duplicated
- Key proteins used in
replication are being
made
G1 phase
M phase
S phase
After all the chromosomes have duplicated in
the S phase, the cell then moves to the next
phase in it’s life called the “G2 phase”
- Cell organelles and
molecules required for cell
division are being made.
G1 phase
M phase
G2 phase
S phase
Next comes the “M phase” which stands for
Mitosis.
Mitosis is the actual cell division of one cell
into two “daughter cells”
Mitosis has 4 parts
in which we will
cover each
M phase
separately.
G1 phase
G2 phase
S phase
Mitosis has 4 steps to it:
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
I’ll show you how to
draw a simple
illustration for each
step for your notes.
But first, let’s review 3 critical events during
interphase just before the cell prepares to go
into Mitosis.
Early Prophase
1. The cell has
divided all it’s
DNA
2. The Nucleolus
disappears
3. The Centrioles
appear
4. It is now ready
to divide.
PROPHASE
1. Chromosomes
form and then
duplicate into
“sister chromatids.”
2. The Nuclear
envelope slowly
disappears
3. The centrioles
head to the poles
4. Spindle fibers start
to appear
“In the military
you form a line”
METAPHASE
1. The sister
chromatids line up in
a straight line along
the “Metaphase
Plate”
2. Spindle fibers
attach to the
chromosomes
near the middle
called a
Kinetochore
ANAPHASE
1. The spindle fibers
pull apart the sister
chromatids and
pulls each
chromosome
toward its pole.
“Ana is a cheerleader – Cheerleaders do the splits”
TELOPHASE
1. The Centrioles fade
away.
2. The nuclear envelope
starts to form
3. The chromosomes
start to unwind to long
strands
4. The cell starts to
pinch in the center
ready to split.
OK, we’re almost done, but the cell still has
one more thing to go through before it gets
out of the “m phase”
Cytokinesis
M phase
Cytokinesis Animal Cell
1. The Cell now has two
separate nuclei
2. The Cell then pinches in
the middle and splits in two
3. The 2 cells have the exact
same DNA in each cells
4. The two cells are now
called “Daughter Cells”
Movie Mitosis
Cytokinesis Plant Cell
1. Vesicles containing cell wall material forms a plate line
2. The vesicles connect to form a cell plate
3. The cell plate divides the daughter cells and becomes
a cell wall.
Now could you identify the
phase in a real cell?
ANAPHASE
METAPHASE
PROPHASE
CYTOKINESIS –
(PLANT)
TELOPHASE
PROPHASE
METAPHASE PROPHASE
ANAPHASE
Late ANAPHASE or EARLY TELOPHASE
The important thing to remember is that your two
daughter cells
(the final product of Mitosis)
Will have the same number of chromosomes as the
original cell did.
46
Mitosis →
Daughter Cells →
46 + 46
46
46
VOCABULARY !
Chromosome
Histome
Nucleosome
Super coils
Centromere
Chromatids
Interphase
Cell cycle
G1 phase
S phase
G2 phase
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Cell plate