Download The Cell Cycle

How do you get to be 6 ft tall if
you started out as a single cell?
How do you heal a wound?
How do you replace worn out
cells?
Cell cycle and Cell Division
Ability to reproduce is one characteristic that
distinguishes living things from nonliving
matter.
The continuity of life from one cell to
another is based on cell division
This division process occurs as part of the
cell cycle
cell division
Cells come from cells
Cell division is needed for
growth, replacement and repair
Body cells are called somatic cells
Sex cells are called gametes
What is Mitosis?
Mitosis
Takes one cell and produce two cells that are
the genetic equivalent of the parent.
Mitosis is nuclear division. It is the process by
which a new cell receives the identical DNA as
its parent cell
The new cell is called the daughter cell. Mitosis
produces two identical daughter cells
Why is mitosis important?
This is how multicellular organisms grow,
repair or heal injuries and maintain
function.
It is also how asexual reproduction takes
place
Mitosis accompanied by Cytokinesis
Functions in reproduction,
growth, and repair
– reproduces an entire unicellular
organism, increasing the
population.
– on a larger scale can produce
progeny for some multicellular
organisms.
• organisms
that can grow by cuttings
or by fission.
• Is central to the development of a multicellular
organism that begins as a fertilized egg or
zygote.
• For repair and renew cells that die from normal
wear and tear or accidents.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Prokaryotes( bacteria) reproduce by binary
fission
– Prokaryotic cells
• Reproduce asexually by cell division
Colorized TEM 32,500
Prokaryotic chromosomes
Figure 8.3B
What is a genome?
An organism’s complete collection
of all its genes
DNA is the molecule that makes up
your genes
DNA is packaged into units called
chromosomes in the nucleus of cells
What is DNA?
DNA or deoxyribonucleic acid is a
large molecule made of chains of
repeating units called nucleotides.
It contains the information for
specifying the proteins that allow life
What kind of information is
encoded in DNA?
Instructions on how to make proteins.
Organisms function as a result of its proteins.
Proteins make up structural parts and function as
defenses, hormones, enzymes, transport among
many others
What is a gene?
A segment of DNA on a chromosome
containing instruction on how to
make a protein
What are chromosomes?
A DNA molecule with its
associated proteins called
histones
The number of chromosomes is the
same for all the members of a species.
Humans have 46 chromosomes
What is the HAPLOID number of
chromosomes? What is DIPLOID?
• What cells have the haploid number? Why?
• What cells have the diploid number of
chromosomes? Why?
– Before a cell starts dividing, the chromosomes replicate
– Producing sister
chromatids joined
together at the
Sister chromatids
centromere
TEM 36,000
Centromere
Figure 8.4B
Where are the chromosomes
found?
Chromosomes are found in the
nucleus of eukaryotic cells
Chromosome
one chromosome (unduplicated)
one chromosome (duplicated)
Chromosome Number
• Sum total of chromosomes in a cell
• Somatic cells (body cells)
– Chromosome number is diploid (2n)
– Two of each type of chromosome
• Gametes ( sex cells)
– Chromosome number is haploid (n)
– One of each chromosome type
–
One
–
Chr om osom e
of
each
•
Gametes
•
Somatic
•
Sum
chr om osom e
–
Two
–
Chr om osom e
of
each
num b
er
ty
pe
of
is
ty
pe
haploi d
( n)
chr om osom e
num b
er
is
dipl oid
(2 n)
cells
total
of
chromosomes
Chromosome
in
a
cell
Number
-Chromosomes contain a very long DNA molecule
associated with proteins
• And are visible only when the cell is dividing
– If a cell is not undergoing division
Figure 8.4A
LM 600
• Chromosomes
occur in the
form of thin,
loosely packed
chromatin fibers
– Before a cell starts dividing, the chromosomes replicate
– Producing sister
chromatids joined
together at the
Sister chromatids
centromere
TEM 36,000
Centromere
Figure 8.4B
What must happen before
mitosis?
The cell must make exact copies of its
chromosomes in the nucleus so each
new daughter cell gets the same
number and type of chromosomes as
its parent cell
Cell division requires the distribution of
genetic material - DNA - to two
daughter cells.
A dividing cell duplicates its DNA, moves the two
copies to opposite ends of the cell, and then splits
into two daughter cells.
chromosome (unduplicated)
in a cell at interphase
same chromosome (duplicated)
in interphase prior to mitosis
mitosis, cytoplasmic division
chromosome (unduplicated)
in a daughter cell at interphase
chromosome (unduplicated)
in a daughter cell at interphase
Fig. 8.6, p. 131
Slide 4
– Cell division involves the separation of sister
chromatids
• results in two
daughter cells,
each containing
a complete and
identical set of
chromosomes
Chromosome
duplication
Centromere
Sister
chromatids
Chromosome
distribution
to
daughter
cells
Figure 8.4C
What is the cell cycle?
The cell cycle is an ordered set of events,
resulting in cell growth
and division into two daughter cells
The stages of the cell cycle are :
G1(stands for Gap1),
S (stands for synthesis, this is when DNA is replicated) and
G2 (stands for Gap 2)
Cell Cycle
• Cycle starts when a new cell forms
• During cycle, cell increases in mass
and duplicates its chromosomes
• Cycle ends when the new cell divides
The Cell Cycle
What are the phases of the cell
cycle?
Interphase: This takes up most of the cell cycle
G1This is a time when a cell doubles organelles in
its cytoplasm and grows
S is when DNA in the nucleus is doubled
G2 each chromosome now consists of two identical
sister chromatids and the cell is preparing to divide
Mitosis: the nucleus and its duplicated
chromosomes divide
Cytokynesis: the cytoplasm is divided in two
The mitotic phase alternates with
interphase in the cell cycle
• The mitotic (M) phase of the cell
cycle alternates with the much
longer interphase.
– The M phase includes mitosis and
cytokinesis.
– Interphase accounts
for 90% of the cell
cycle.
Interphase
•Usually longest part of the cycle
•Cell increases in mass
•Number of cytoplasmic
components doubles
•DNA is duplicated
Stages of Interphase
•G1
–Interval or gap after cell division
•S
–Time of DNA synthesis (replication)
•G2
–Interval or gap after DNA replication
Mitosis
•Period of nuclear division
•Usually followed by cytoplasmic
division - Cytokynesis
The four stages of mitosis
Prophase
Metaphase
Anaphase
telophase
Fig. 12.9
Fig. 12.5 left
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 12.5 right
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• On the cytoplasmic
side of the cleavage
furrow a contractile
ring of actin
microfilaments and the
motor protein myosin
form.
• Contraction of the ring
pinches the cell in two.
Fig. 12.8a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Cytokinesis divides the cytoplasm:
a closer look
• Cytokinesis, division of
the cytoplasm, typically
follows mitosis.
• In animals, the first sign
of cytokinesis (cleavage)
is the appearance of a
cleavage furrow in the
cell surface near the old
metaphase plate.
Fig. 12.8a
Cell plate
forming
Wall of
parent cell
Daughter
nucleus
– In plants
TEM 7,500
• A membranous cell
plate splits the cell
in two
Cell wall
Vesicles containing
cell wall material
Figure 8.7B
New cell wall
Cell plate
Daughter cells
Check these web sites:
• http://www.cellsalive.com
• http://www.biology.arizona.edu/cell_bio/cell_bio.html
• http://www.loci.wisc.edu/outreach/bioclips/CDBio.
html
• http://gslc.genetics.utah.edu/units/stemcells/whatis
sc
Play this game:
• http://science.nhmccd.edu/biol/bio1int.htm
Control System of the Cell Cycle
• The distinct events of the cell cycle are directed by a distinct
cell cycle control system.
– These molecules trigger and coordinate key events in the cell
cycle.
– The control cycle has
a built-in clock, but it
is also regulated by
external adjustments
and internal controls.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Cell cycle control system
• There are three major checkpoints in the cell
cycle. These are “stop and go” signals.(G1, M,
and G2)
• It checks whether or not the cellular processes
have been completed up to that point so it can
proceed.
• The G1 check point is very important. Nerve
cells and muscle cells switch into a non
dividing stage called G0. They do not get a
“go ahead” signal and stop dividing.
Regulation of the cell cycle
How cell division is regulated is very
complex and when there are errors it
results in cancer
Cancer is a disease where control of
cell division is lost. The cells don’t
grow or behave normally
An example of a cell cycle
control is p53
P53 is a protein that functions to
block the cell cycle if the DNA is
damaged
A p53 mutation ( non functioning or
reduced levels)is the most frequent
mutation leading to cancer
• A variety of chemical and physical factors can influence cell
division.
Important for mammalian cells are growth factors, proteins
released by one group of cells that stimulate other cells to
divide.
• Each cell type responds specifically to a certain growth factor or
combination of factors.
– For example, platelet-derived growth factors (PDGF),
produced by platelet blood cells, bind to tyrosine-kinase
receptors of fibroblasts, a type of connective tissue cell.
– This triggers a signal-transduction pathway that leads to
cell division.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The role of PDGF is easily seen in cell culture.
– Fibroblasts in culture will only divide in the presence of
medium that also contains PDGF.
Fig. 12.15
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Growth factors appear to be a key in density-dependent
inhibition of cell division.
– Cultured cells normally
divide until they form a
single layer on the inner
surface of the culture
container.
– If a gap is created, the
cells will grow to fill
the gap.
– At high densities, the
amount of growth factors
and nutrients is insufficient to allow cell growth and division stops.
Fig. 12.16a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Most animal cells also exhibit anchorage dependence
for cell division.
– To divide they must be anchored to a substratum,
typically the extracellular matrix of a tissue.
– Control appears to be mediated by connections
between the extracellular matrix and plasma
membrane proteins and cytoskeletal elements.
• Cancer cells are free of both density-dependent
inhibition and anchorage dependence.
Fig. 12.16b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
tumors
Growing out of control, cancer cells produces
malignant tumors
– Cancer cells
• divide excessively to form masses called tumors
Tumors can be benign and malignant (cancerous
neoplasm)
Fig. 12.17
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
What is a metastasis?
1.Cancer cells break away from tumor
2. Cancer cells migrate to blood vessels. These cells
are able to secrete enzymes that open vessel wall
and enter the blood stream or lymph.
3. Cells move with the blood, exit vessel and invade
a new site.
4. This new growth on a new site is a metastasis
– Radiation and chemotherapy
• Are effective as cancer treatments because they
interfere with cell division
Web sites about cancer:
http://outreach.mcb.harvard.edu/animations_S03.htm
• About mitosis:
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter11/animati
ons.html
Check these web sites:
• http://www.cellsalive.com
• http:/www.biology.arizona.edu/cell_bio/tutorials/cell_cycl
e/cells2.html
• http://www.loci.wisc.edu/outreach/bioclips/CDBio.html
• http://gslc.genetics.utah.edu/units/stemcells/whatissc
Play this game:
• http://science.nhmccd.edu/biol/bio1int.htm
Comparison of mitosis and meiosis
• MITOSIS
-OCCURS IN ALL SOMATIC CELLS
•
•
-PRODUCES IDENTICAL COPIES
OF PARENT CELL. Daughter cell has
same number of chromosomes as parent.
MEIOSIS
-OCCURS ONLY IN SEX CELLS:
GAMETES (ova or eggs and sperm)
- PRODUCES VARIATION IN
TRAITS
-RESULTS IN 2 DIPLOID (2n) cells
complete number of chromosomes
•
-ONE REPLICATION OF CHROMOSOMES
FOLLOWED BY 1 CELL DIVISION
- Results in 4 haploid (n) cells
reduced number of chromosomes
- ONE REPLICATION OF
CHROMOSOMES
FOLLOWED BY 2 CELL DIVISIONS
FACTORS THAT CONTRIBUTE TO
GENETIC VARIATION
MUTATIONS
CROSSING OVER DURING PROPHASE I
OF MEIOSIS
INDEPENDENT ASSORTMENT OF
CHROMOSOMES during meiosis
RANDOM FERTILIZATION OF THE
EGG BY SPERM