Download The Cell Cycle

Cell Growth
&
Reproduction
Section 8.2
Chapter 8
Pages 203 - 210
Cell Reproduction
All cells come from preexisting cells.
Cell division is the way that new cells are
produced from one cell.
Cell Reproduction
Cell division gives
you two cells that
are identical to
the original or
parent cell.
Cell Reproduction
Cells are
constantly
getting old,
dying and
being
replaced.
New cells are
needed for
growth.
The Discovery of Chromosomes
Early biologists observed that stringy
structures appeared in the nucleus just before
cell division.
They also noticed that these structures
seemed to vanish soon after cell division.
These stringy structures are chromosomes.
The Discovery of Chromosomes
Chromosomes contain DNA.
The Discovery of Chromosomes
Chromosomes carry the genetic information
that is copied from one generation to the next.
It is important that this information is
accurately passed along during cell division.
When most of you
think of chromosomes,
this is probably the
image you have in your
head.
Electron scanning microscope’s photo of
chromosomes
Karotype
Humans have 23 pairs of chromosomes
This is a male… the sex chromosomes are an XY pair
The structure of eukaryotic
chromosomes
For most of a cells lifetime, chromosomes
exist as chromatin.
Chromatin are long strands of DNA
wrapped around proteins.
The structure of eukaryotic
chromosomes
Under an electron microscope, chromatin
looks like a string of beads.
The structure of eukaryotic
chromosomes
Before a cell can divide, the long strand of
chromatin needs to be organized… kind of
like when we wrap up a cord to store it.
In this wrapped up coil, the chromatin is
very tightly packed.
Chromosome Structure
The chromosomes
of eukaryotic cells
change shape
depending on which
phases of the cell
cycle they are in.
Chromosome Structure
A metaphase
chromosome is a
compact arrangement
of DNA.
Chromosomes during
interphase are long and
tangled.
The Cell Cycle
What kind of cycles can you think of?
Seasons, tides, day and night…
Cells have cycles too.
The cell cycle is the sequence
of growth & division.
There are two periods in the cell cycle.
One period is for growth,
the other is for division.
Interphase
Interphase is the growth period.
Most of the cells life is spent in
interphase.
Interphase
During interphase a cell:
•grows in size
•carries on metabolic functions
•duplicates chromosomes for
division
Mitosis is the period of division.
Mitosis
During mitosis, two daughter cells
are formed from one parent cell.
Each daughter cell has a complete
set of chromosomes.
After mitosis, the cytoplasm divides
to separate the two daughter cells.
The Cell Cycle
S phase
G1 phase
G2 phase
M phase
Interphase is the busiest time
of the cell cycle.
Interphase is divided into three parts:
G1
The cell grows and protein production is
high.
S
The cell copies its chromosomes. This is
the only time during the cell cycle that
DNA synthesis occurs.
G2 The cell then enters another growth
period where mitochondria and other
organelles are manufactured and other
parts needed for cell division are
produced.
Interphase now ends
and mitosis begins!
The Phases of Mitosis
Cells undergo mitosis when they reach
maximum cell size.
Remember, a cell can only grow so large until
the surface area of the cell membrane
becomes too small in proportion to its
volume.
The cell membrane transports nutrients and
waste into and out of the cell.
Although cell division is a continuous process, it can be
broken up into four phases.
The 4 phases of mitosis are:
prophase
metaphase
anaphase
telophase
How long does the cell cycle take?
• Each turn of the cell cycle is a generation.
• Generation time varies greatly depending on the
species and type of cell.
• The minimum time needed is about 10 minutes.
• It takes about 2 hours for sea urchin cells to
divide.
• Most growing plant and animal cells need 8 – 10
hours to divide.
How long does the cell cycle take?
• The generation time for a bean seed is 19
hours
• The G1 phase lasts about 5 hours
• The S phase lasts about 7 hours
• The G2 phase lasts about 5 hours
• The M phase lasts about 2 hours
How long does the cell cycle take?
• The generation time for some mouse cells
is about 22 hours
• The G1 phase lasts about 9 hours
• The S phase lasts about 10 hours
• The G2 phase lasts about 2 hours
• The M phase lasts about 1 hour
How long does the cell cycle take?
• Many mature
cells like nerve
cells and red
blood cells,
never divide.
• They are said
to be in the G0
phase which is a
lot like the G1
phase.
Mitosis Notes
Cell Division occurs in a series
of stages, or phases.
st
1
phase: Interphase
• (Not mitosis… but part of the cell cycle!)
• Chromosomes are copied (# doubles)
• Chromosomes appears as threadlike coils
(chromatin) at the start, but each
chromosome and its copy (sister
chromosome) change to sister chromatids
at the end of this phase
Interphase
2
2nd phase: Prophase
• Mitosis begins (cell begins to divide)
• Centrioles (or poles appear and begin
to move to opposite ends of cell
• Spindle fibers form between the
poles
Prophase
4
Prophase
Spindle fibers
Disappearing
nuclear envelope
Doubled
chromosome
Prophase: the first phase of mitosis
•longest phase of mitosis.
•The long stringy chromatin coils up into
visible chromosomes.
•Each chromosome is made of two halves.
Prophase: the first phase of mitosis
The two halves of the doubled structure
are called sister chromatids.
Sister chromosomes are an exact copy of
each other.
Sister chromosomes are made when DNA is
copied during interphase.
Sister chromatids are held together with a
structure called a centromere.
2 sister chromatids held
together with a centromere
telomeres
centromere
2 sister chromatids
Centromeres play a
role in chromosome
movement during
mitosis.
The position of the
centromere also
helps scientists
identify the
chromosomes.
As prophase continues, the nucleus
disappears as the nuclear envelop and
the nucleolus disintegrate.
In animal cells, pairs of structures
called centrioles migrate to opposite
ends of the cell.
Centrioles are small, dark, cylindrical
structures that are made of small
tubes.
Centrioles play a role in chromatid
separation.
As the pairs of centrioles move to
the opposite ends, another
structure called spindles, form
between them.
The spindle fibers make a cage like
structure made of microtubules.
Plant cells form spindles without
centrioles.
The spindle fibers separate sister
chromatids during mitosis.
rd
3
phase : Metaphase
• Chromatids (or pairs of
chromosomes) attach to the spindle
fibers
Metaphase
7
Metaphase
Centromere
Sister chromatids
Metaphase:
The second stage of mitosis
Metaphase is a short stage.
The sister chromosomes become attached
to spindle fibers by their centromeres.
The spindle fibers pull on the chromatids
until they line up in the center of the cell.
Metaphase:
The second stage of mitosis
Each sister chromatid is attached to
its own spindle fiber.
This helps to ensure that each new cell
receives an identical and complete set
of chromosomes.
4th phase : Anaphase
• Chromatids (or pairs of
chromosomes) separate and begin to
move to opposite ends of the cell
Anaphase
10
Anaphase
Anaphase:
The third phases of mitosis
The separation of sister chromatids is the
beginning of anaphases.
During anaphase, the centromeres split apart
and chromatid pairs from each chromosome
separate.
The chromatids are pulled apart by the
shortening of the microtubules on the spindle
fibers.
5th phase : Telophase
• Two new nuclei form
• Chromosomes appear as chromatin
(threads rather than rods)
• Mitosis ends
Telophase
13
Telophase
Nuclear
envelope
reappears
Telophase:
The fourth phase of mitosis
Telophase begins as the chromatids reach
the opposite sides of the cell.
During telophase, many of the changes
that occurred during prophase are
reversed.
Telophase:
The fourth phase of mitosis
The chromosomes which were tightly coiled
since the end of prophase are now unwinding.
The spindles breakdown, the nucleolus
reappears, and a new nuclear envelope forms
around each set of chromosomes.
Finally a new double membrane begins to form
between the two nuclei.
6th phase : Cytokinesis
• Cell membrane moves inward to
create two daughter cells – each with
its own nucleus with identical
chromosomes
Cytokinesis
16
Cytokinesis – After Mitosis
After telophase, the cell’s cytoplasm
divides in a process known as cytokinesis.
Cytokinesis is different in plant and animal
cells.
With animal cells,
towards the end of
telophase, the cell
membrane pinches in
around its equator and
the two new cells are
separated.
This is the furrow
created when the cell
membrane of a frog cell
pinched in two.
Plants have a rigid cell wall so the
plasma membrane does not pinch in.
Instead a structure known as a cell
plate is laid down across the cell’s
equator.
Then cell membrane forms around
each cell and a new cell wall forms on
each side of the cell plate until
separation is complete.
Results of Mitosis
Mitosis results in two new cells with
chromosome sets that are identical to
the parent cell.
The new cells will carry out the same
cellular processes and functions as the
parent cell.
The new cells will grow and divide just
like the parent did.
Results of Mitosis
When mitosis is complete, unicellular
organisms are still unicellular – the
organism simply multiplied!
In multicellular organisms, cell growth and
reproduction result in groups of cells that
work together as tissue.
Tissues work together to form
organs.
Multiple organs work together to
form organ systems.
Organ systems work together for
the survival of the organism.
Levels of organization
Cells of complex multicellular organisms
are organized into
tissues, organs, and organs systems.
The different systems have
developed through cell
specialization.
No matter how complex, the cell is
still the most basic unit of life.