Transcript The Cell Cycle

Chapter 5
The Cell Cycle & Mitosis
Control of the Cell Cycle
Uncontrolled Cell Growth & Cancer
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Review: Surface Area to Volume Ratio
• Organisms must exchange matter with the environment
to grow, reproduce and maintain organization.
• The cellular surface-to-volume ratio affects a biological
system’s ability to obtain resources and eliminate waste
products.
–
As cells increase in volume, the relative surface area decreases and
demand for material resources increases;
–
Large organisms require more cellular structures to adequately
exchange materials and energy with the environment;
–
These limitations restrict cell size – the surface area of the plasma
membrane must be large enough to adequately exchange materials;
–
Smaller cells have a more favorable surface-to-volume ratio for
exchange of materials with the environment.
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Overview: The Key Roles of Cell Division
• In unicellular organisms, division of one cell
reproduces the entire organism
• Multicellular organisms depend on cell division
for:
– Development from a fertilized cell
– Growth
– Repair
• Cell division is an integral part of the cell cycle,
the life of a cell from formation to its own
division
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Fig. 12-2
100 µm
(a) Reproduction
20 µm
200 µm
(b) Growth and
development
(c) Tissue renewal
Cell Division
• Most cell division results in daughter cells with
identical genetic information, DNA
• MITOSIS
• A special type of division produces nonidentical
daughter cells (gametes, or sperm and egg
cells)
• MEIOSIS
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Cellular Organization of the Genetic Material
• All the DNA in a cell constitutes the cell’s
genome
• A genome can consist of a single DNA
molecule (common in prokaryotic cells) or a
number of DNA molecules (common in
eukaryotic cells)
• DNA molecules in a cell are packaged into
chromosomes
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Cellular Organization of the Genetic Material
• Every eukaryotic species has a characteristic
number of chromosomes in each cell nucleus
• Somatic cells (nonreproductive cells) have
two sets of chromosomes
• Gametes (reproductive cells: sperm and eggs)
have half as many chromosomes as somatic
cells
• Eukaryotic chromosomes consist of
chromatin, a complex of DNA and protein that
condenses during cell division
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Cellular Organization of the Genetic Material
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Fig. 12-4
0.5 µm
Chromosomes
Chromosome arm
DNA molecules
Chromosome
duplication
(including DNA
synthesis)
Centromere
Sister
chromatids
Separation of
sister chromatids
Centromere
Sister chromatids
Mitosis v. Meiosis
• Eukaryotic cell division consists of:
–
Mitosis, the division of the nucleus
–
Cytokinesis, the division of the cytoplasm
–
Alternating with interphase in the cell cycle, mitosis followed by cytokinesis
provides a mechanism in which each daughter cell receives an identical and a
complete complement of chromosomes.
–
Mitosis ensures fidelity in the transmission of heritable information, and
production of identical progeny allows organisms to grow, replace cells, and
reproduce asexually.
• Sexual reproduction, however, involves the recombination of
heritable information from both parents through fusion of
gametes during fertilization.
–
Gametes are produced by a variation of cell division called meiosis.
–
Meiosis yields nonidentical daughter cells that have only one set of chromosomes,
half as many as the parent cell.
–
Meiosis followed by fertilization provides a spectrum of possible phenotypes
in offspring and on which natural selection operates.
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Phases of the Cell Cycle
• The cell cycle is a complex set of stages that is highly
regulated with checkpoints, which determine the ultimate
fate of the cell.
• The cell cycle consists of
–
Interphase (cell growth, synthesis of DNA and preparation
for division/mitosis)
–
Mitotic (M) phase (mitosis and cytokinesis)
• Mitosis alternates with interphase in the cell cycle to pass a
complete genome from the parent cell to daughter cells.
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__
how_the_cell_cycle_works.html
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Events of the Cell Cycle
Nuclear
division
(M phase)
cell divides
Interphase (period of rest and preparation) is divided into 3 phases:
1.
G1 – cell growth
2.
S – DNA replication
3.
G2 – preparation for Mitosis
*During Interphase, chromosomes are in their “uncondensed” form and are called chromatin.
Mitosis (division of the nucleus) occurs in 4 phases:
1.
P = prophase – chromatin condenses into chromosomes, the centrioles
separate & nuclear membrane breaks down
2.
M = metaphase – chromosomes line up across center of cell and each
chromosome is connected to a spindle fiber at its centromere
3.
A = anaphase – sister chromatids separate into individual chromosomes and
are pulled apart
4.
T = telophase – chromosomes gather at opposite ends of the cell and 2 new
nuclear membranes form around them
*During mitosis, chromosomes are in their “uncondensed” form and are called chromatin.
Cytokinesis – division of cytoplasm – well underway by late telophase
Fig. 12-6
G2 of Interphase
Centrosomes
Chromatin
(with centriole (duplicated)
pairs)
Prophase
Early mitotic Aster Centromere
spindle
Nucleolus Nuclear Plasma
envelope membrane
Chromosome, consisting
of two sister chromatids
Metaphase
Prometaphase
Fragments Nonkinetochore
of nuclear
microtubules
envelope
Kinetochore
Kinetochore
microtubule
Anaphase
Cleavage
furrow
Metaphase
plate
Spindle
Centrosome at
one spindle pole
Telophase and Cytokinesis
Daughter
chromosomes
Nuclear
envelope
forming
Nucleolus
forming
Review: The Cell Cycle
• Mitosis passes a complete genome from the
parent cell to daughter cells.
–
Mitosis occurs after DNA replication during interphase/S phase.
–
Mitosis followed by cytokinesis produces two genetically
identical daughter cells.
–
Mitosis plays a role in growth, repair, and asexual reproduction.
–
Mitosis is a continuous process with observable structural
features along the mitotic process (replication, alignment,
separation).
–
Mitosis alternates with interphase in the cell cycle.
–
The entire cell cycle is directed by internal controls or
checkpoints.
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The Mitotic Spindle: A Closer Look
• Many of the events of mitosis depend on the
mitotic spindle, which begins to form in the
cytoplasm during prophase.
• The mitotic spindle consists of fibers made of
microtubules and associated proteins.
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Fig. 12-7
Aster
Centrosome
Sister
chromatids
Microtubules
Chromosomes
Metaphase
plate
Kinetochores
Centrosome
1 µm
Overlapping
nonkinetochore
microtubules
Kinetochore
microtubules
0.5 µm
Fig. 12-9: Cytokinesis – A Closer Look
100 µm
Cleavage furrow
Contractile ring of
microfilaments
Vesicles
forming
cell plate
Wall of
parent cell
Cell plate
1 µm
New cell wall
Daughter cells
(a) Cleavage of an animal cell (SEM)
Daughter cells
(b) Cell plate formation in a plant cell (TEM)
Mitosis in Animal Cell
Mitosis in Plant Cell
Nucleus
Nucleolus
1 Prophase
Chromatin
condensing
Chromosomes
2 Prometaphase
3 Metaphase
Cell plate
4 Anaphase
5 Telophase
10 µm
Binary Fission
• Prokaryotes (bacteria and
archaea) reproduce by a
type of cell division called
binary fission
• In binary fission, the
chromosome replicates
(beginning at the origin of
replication), and the two
daughter chromosomes
actively move apart
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Concept 12.3: Control of the Cell Cycle
• How do cells know when to divide? Cell division in
eukaryotes is highly complex. Some mechanisms
of cell cycle control include:
– Presence of proteins called cyclins (internal
regulators and external regulators):
• Internal Regulators: respond to events inside the cell – hold
cell in interphase until all chromosomes are copied.
• External Regulators: respond to events outside the cell and
direct cells to speed up or slow down the cell cycle.
– Closeness of neighboring cells:
• Density-dependence inhibition causes cells to stop dividing
when they come in close contact with each other.
• Anchorage dependence allows cells to divide only when
anchored to a substrate.
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Cell Cycle Checkpoints
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At each of these checkpoints,
the cell checks that it has
completed all of the tasks
needed and is ready to
proceed to the next step in its
cycle.
THESE CELL CYCLE
CHECKPOINTS FUNCTION
TO ENSURE THAT
COMPLETE GENOMES ARE
TRANSMITTED TO
DAUGHTER CELLS!
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KINASES: The Protein Regulators of the Cell Cycle
• Cell Division is tightly controlled by complexes made of several
specific proteins.
–
These complexes contain enzymes called cyclin-dependent
kinases (CDKs), which turn on or off the various processes that
take place in cell division.
–
CDK partners with a family of proteins called cyclins.
–
One such complex formed by the fusion of CDK and cyclin is
mitosis-promoting factor (MPF), sometimes called maturationpromoting factor, which contains cyclin A or B and cyclindependent kinases (CDK).
–
CDK is activated when it is bound to cyclin (thus producing MPF),
interacting with various other proteins that, in this case, allow the
cell to proceed from G2 to mitosis.
–
The levels of cyclin change during the cell cycle, shutting on and
off the mitotic phases.
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MPF and Cell Cycle Control at G2 Checkpoint
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Growth Factors and Cell Cycle Control
• EXTERNAL factors, both chemical and
physical, can influence cell division.
• Even when all other conditions are
favorable, most mammalian cells divide only
in the presence of specific growth factors.
• Growth factors are proteins that are
released by certain cells that stimulate other
cells to divide.
– These are local regulators – they travel short
distances influence only cells in close vicinity.
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PDGF and Cell Cycle Control
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Contact Cell Cycle Control
• Contact cell cycle control mechanisms include
density-dependent inhibition and anchorage
dependence.
– In density-dependent inhibition, crowded
cells stop dividing.
– Anchorage dependence is a phenomenon in
which cells must be attached to a substratum
(i.e. extracellular matrix of a tissue) in order to
divide.
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Fig. 12-19
Anchorage dependence
Density-dependent inhibition
Density-dependent inhibition
25 µm
25 µm
(a) Normal mammalian cells
(b) Cancer cells
Loss of Cell Cycle Controls in Cancer Cells
• The cell cycle is regulated very precisely. Mutations in cell cycle
genes that interfere with proper cell cycle control are found very
often in cancer cells.
• Cancer cells do not respond normally to the body’s control:
–
They exhibit neither density-dependent inhibition nor anchorage
dependence.
–
They may not need growth factors to grow and divide.
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Cancer Cells and the Formation of Tumors
• A normal cell is converted to a cancerous cell
by a process called transformation
• Cancer cells form tumors, masses of abnormal
cells within otherwise normal tissue
• If abnormal cells remain at the original site, the
lump is called a benign tumor
• Malignant tumors invade surrounding tissues
and can metastasize, exporting cancer cells to
other parts of the body, where they may form
secondary tumors
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Fig. 12-20
http://www.youtube.com/watch?v=IeUANxFVXKc
Lymph
vessel
Tumor
Blood
vessel
Cancer
cell
Metastatic
tumor
Glandular
tissue
1 A tumor grows
from a single
cancer cell.
2 Cancer cells
invade neighboring tissue.
3 Cancer cells spread
to other parts of
the body.
4 Cancer cells may
survive and
establish a new
tumor in another
part of the body.