Mitosis
&
The Cell Cycle
Unit – Cell Reproduction
Biology
How many cells do you
think your body has?
Each of us began as a single cell,
so one important question is:
How did that single cell develop
into a body with more than a
trillion cells?
Cell Division
The production of such a large number of
body cells is accomplished by many, many
repeats of a cycle of cell division in which
one cell gives rise to two cells, each of
which in turn gives rise to two cells, etc.
Thus, cell division is needed for growth.
Even in a fully grown adult, cells still
undergo cell division.
Why is this useful?
Think about your skin, for example.
Cell Division
The two cells that come from the division of
one cell are called daughter cells.
Each of the daughter cells needs to have a
complete set of chromosomes.
What are chromosomes?
Chromosomes
are
compact
spools
of
DNA
Chromosomes
• The chromosome (left in the picture) was
isolated from a dividing cell.
• Notice that the chromosome
consists of two identical
halves
• Each half is
called a
chromatid
Chromosomes
The point
where the
two
chromatids
touch and
are held
together is
called a
centromere
Review chromosome structure
Let’s make some chromosomes
Obtain 2 white pipe cleaners and 2 of
another color.
Cut white pipe cleaners into 2:
4 inch long pieces
3 inch long
2 inch long
1½ inch long
Let’s make some chromosomes
• Pick two different colored beads. You will
need 8 of each color
• Put one of the colored beads on each of
the white pipe cleaners and move them to
the center of the pip cleaners.
• Repeat by putting one of the other colored
beads on each of the colored pipe
cleaners
Chromosome Numbers
Each species has a certain number of
chromosomes in each cell.
46
78
18
52
Sex chromosomes
• Chromosomes that determine the sex of
the organism
• In humans, sex chromosomes are either X
or Y
XX
XY
Autosomes
• All the other chromosomes in an organism
Unsorted Human Chromosomes
Karyotype
Photomicrograph
of the
chromosomes in
a dividing cell
found in a human
What is the sex
of the person
whose
chromosomes
are shown here?
Question
• What percent of your genes come from
your mom?
• What percent of your genes come from
your dad?
Where did my chromosomes come
from?
• We inherit one member of each
chromosome pair from each parent.
Where did my chromosomes come
from?
• The 46 chromosomes in our somatic cells
are actually two sets of 23
chromosomes—a maternal set (from our
mother) and a paternal set (from our
father.)
Homologous chromosomes
• The two copies of each chromosome
• They are the same size and shape and
carry genes for the same traits
Diploid Cells
• Cells having two sets of chromosomes
• All normal human cells are diploid cells
(except reproductive cells – egg and
sperm cells)
• Commonly abbreviated as 2n
• In humans the diploid number is 46
Haploid Cells
• Human sperm cells and egg cells
Haploid Cells
• Contain only 1 set of chromosomes
• Haploid cells have only 1 chromosome of
each homologous pair and only 1 sex
chromosome
• Abbreviated as 1n
• When a sperm (1n) and egg cell (1n)
combine, the new cell will be diploid (2n)
A comparison
Haploid
Diploid
Cell Division
How do you think each
daughter cell gets a
complete set of
chromosomes?
In each cycle of cell
division, the cell first
makes a copy of all of the
DNA in each of the
chromosomes.
Cell Division
After the DNA in each chromosome has
been copied, the cell undergoes a type of
cell division called mitosis, which carefully
separates the two copies of each
chromosome to opposite ends of the
dividing cell, so each daughter cell ends
up with a complete set of chromosomes.
What is the cell cycle?
• The repeating set of events that make up
the life of a cell
• Cell division is one phase of the cell cycle
What is the cell cycle?
• Interphase
– G1, S, G2 phase
• Mitosis (M phase)
– Prophase
– Metaphase
– Anaphase
– Telophase
• Cytokinesis
Interphase
• The time between cell divisions
• Divided into 3 phases (G1, S, G2 phases)
G1 phase
• Offspring cells grow to mature size
S phase
Cell’s DNA is copied
S phase
Cell’s DNA is
copied
G2 phase
The time to prepare for cell division
G2 phase
• Centrosomes – two pairs of dark spots; it
is the microtubule organizing center
• Centrioles - structures in the cytoplasm
from which the spindle fibers form
G0 phase
• Cells can exit the cell cycle and enter a
state called the G0 phase
• Cells do not copy DNA and do not prepare
for cell division
Mitosis
Division of the nucleus
Prophase
• DNA tightens
and coils into
chromosomes
• Nuclear
membrane
breaks down
and disappears
Metaphase
• Chromosomes
line up in the
center of the cell
Anaphase
• The chromatids
of each
chromosome
separate at the
centromere
• chromatids move to
opposite poles of cell
Telophase
• Chromosomes return to
chromatin state
• A nuclear membrane
forms around each set
of chromosomes
Cytokinesis
• The cytoplasm of the cell divides
• The area of the cell membrane
that pinches in and eventually
separates the dividing cell into
two cells is called the cleavage
furrow.
Cytokinesis
Cytokinesis
• Vesicles formed by the
Golgi apparatus fuse at
the midline of the
dividing cell, forming a
membrane-bound cell
wall called the cell plate.
Plant cells in various stages of
mitosis
Cell Cycle
Cancer cells
Cancer cells
Cancer cells
Cancer cells