Transcript Slide 1

Essentials of
Biology
Sylvia S. Mader
Chapter 8
Lecture Outline
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8.1 The Basics of Cellular
Reproduction
• Multicellular organisms begin life as a
single cell
• We become trillions of cells because of
cellular reproduction
• Continues as we grow and replace wornout or damaged tissues
Figure 8.1 Cellular reproduction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
c. Amoebas reproduce
b. Tissues repair
a. Children grow
d. Zygotes develop
a: © Corbis RF; b(tail): © McDonald Wildlife Photography/Animals Animals; b(lizard): © Kevin Hanley/Animals Animals; c: © Biophoto
Associates/Photo Researchers, Inc.; d(left): © Anatomical Travelogue/Photo Researchers, Inc.; d(right): © Brand X
Pictures/PunchStock
•
Asexual reproduction
•
•
•
All cells come from cells
•
•
Doesn’t require sperm or egg
Required in sexual reproduction
Cellular reproduction is necessary for production of
both new cells and new organisms
2 important processes
1. Growth – cell duplicates its contents (including DNA
and organelles)
2. Cell division – parent cell contents divided into two
daughter cells
• Both processes heavily regulated
• Chromosomes
 DNA replication is the copying of DNA
• Full set passed to each daughter cell
 DNA packaged into chromosomes
• Thickened complex of DNA and proteins
• Allows easier distribution to daughter cells
• Chromatin
 DNA and associated proteins have
appearance of thin threads
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Chromosome: duplicated and condensed
• DNA periodically
wound around
histones to form
nucleosomes
• Just before cell
division, chromatin
condenses into
chromosomes
• Humans have 46
chromosomes
sister
chromatids
centromere
×8,400
looped
chromatin
zigzag
chromatin
Chromatin: beads-on-a-string
nucleosomes
histones
(chromatin): Courtesy O.L. Miller, Jr. and Steve L. McKnight; (chromosome): © Biophoto Associates/Photo Researchers, Inc.
Figure 8.2
Chromosome
compaction
• Duplicated chromosomes composed of
sister chromatids joined at centromere
 Each sister chromatid has identical DNA
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chromosome
consisting
of one
chromatid
duplicated
chromosome
duplication
centromere
sister
chromatids
Figure 8.4
8.2 The Cell Cycle
• Orderly sequence of stages that takes
place between the time a new cell has
arisen and to the point where it gives rise
to two daughter cells
• Interphase
• M (Mitotic) Stage
Figure 8.3 The cell cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Growth occurs as
organelles double.
G0
G1
M
Mitosis and
cytokinesis
occur.
G2
S
Growth occurs
as cell prepares
to divide.
DNA replication
occurs as
chromosomes
duplicate.
• Interphase
 Majority of the cell cycle
 Time when a cell performs its usual
functions
 Amount of time varies widely depending
on cell
 3 stages
• G1
• S – DNA synthesis
• G2
• Interphase
 3 stages
• G1 – stage before DNA replication
 Cell doubles organelles
 Accumulates materials for DNA synthesis
 Makes decision whether to divide or not
 G0 – arrested – does not go on to divide
• S – DNA synthesis
 Results in each chromosome composed of two
sister chromatids
• G2 – stage following DNA synthesis
 Extends to onset of mitosis
 Synthesizes proteins needed for cell division
• M (mitotic) phase
 Cell division occurs
 Encompasses
• Division of nucleus (mitosis)
 Creates two identical daughter nuclei
• Division of cytoplasm (cytokinesis)
8.3 Mitosis and cytokinesis
• Distributes duplicated nuclear contents of parent cell
equally to daughter cells
• Each sister chromatid has the same genetic information
• Daughter chromosomes – separated sister chromatids
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chromosome
consisting
of one
chromatid
duplication
Figure 8.4 Overview of mitosis
duplicated
chromosome
mitosis
centromere
sister
chromatids
daughter
chromosomes
• Daughter nuclei produced by mitosis are
genetically identical to each other and the
parent nucleus.
• Every animal has an even number of
chromosomes – each parent contributes
half of the chromosomes to the new
individual.
 In drawings, colors may be used to indicate
chromosomes contributed by the male or
female parent.
• Spindle
 Most eukaryotic cells rely on this structure to
pull chromatids apart.
 Part of cytoskeleton
 Spindle fibers are made of microtubules
 Centrosome – primary microtubule organizing
center
 Spindle fibers may overlap at the spindle
equator or attach to duplicated chromosomes.
• Mitosis is a continuous process
• Traditionally divided into 4 phases




Prophase
Metaphase
Anaphase
Telophase
• Plant and animal cells differ
 Plant – have centrosomes but lack centrioles
 Animal – each centrosome has 2 centrioles
and an aster (array of microtubules)
Figure 8.5 Mitosis in a plant cell
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condensing
chromosomes
nucleus
with
chromatin
Interphase
5
Prophase
5
chromosomes
spindle equator
Metaphase
5
Courtesy Dr. Andrew S. Bajer, University of Oregon
Figure 8.5 Mitosis in a plant cell (continued)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
spindle fibers
(pink)
pole
Anaphase
Telophase
×5
Courtesy Dr. Andrew S. Bajer, University of Oregon
×5
• Phases of mitosis in animal cells
 Although mitosis is divided into phases, it is a
continuous process.
 DNA has been replicated before mitosis
begins.
 Each chromosome consists of 2 sister
chromatids attached at a centromere.
 Red chromosomes are from one parent, blue
are from the other parent.
 Mitosis is usually followed by cytokinesis
• Division of the cytoplasm
• Begins during telophase and continues after the
daughter nuclei have formed
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Cell cycle G1, S, G2
Cell cycle M: Phases of mitosis
Interphase
Prophase
250
250
chromosomes
early mitotic spindle
centrioles in
centrosomes
centrosome
nucleolus
spindle
fibers
chromatin
centromere
nuclear
envelope
chromosome,
consisting of
two sister
chromatids
plasma
membrane
Interphase
During interphase, the eukaryotic
cell duplicates the contents of the
cytoplasm, and DNA replicates in
the nucleus. The duplicated
chromosomes are not yet visible.
A pair of centrosomes is outside
the nucleus.
nuclear
envelope
fragments
Prophase
During prophase, the chromosomes are
Prophase continues with the
condensing. Each consists of two sister
disappearance of the nucleolus and the
chromatids held together at a centromere.
breakdown of the nuclear envelope.
Outside the nucleus, the spindle begins to
Spindle fibers from each pole attach to the
assemble between the separating
chromosomes at specialized protein
centrosomes.
complexes on either side of each
centromere. During attachment, a
chromosome first moves toward one pole
and then toward the other pole.
Figure 8.6 Phases of mitosis in animal cells
(all): © Ed Reschke
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phases of mitosis
Metaphase
Anaphase
Telophase and Cytokinesis
aster
×250
×250
chromosomes
at spindle
equator
×250
daughter chromosomes
cleavage furrow
nucleolus
forming
spindle
pole
nuclear
envelope
forming
Metaphase
During metaphase, the
chromosomes are aligned at the
spindle equator midw ay between
the spindle poles. The spindle
fibers on either side of a
chromosome extend to opposite
poles of the spindle. Unattached
spindle fibers reach beyond the
equator and overlap.
Anaphase
During anaphase, the sister chromatids
separate and become daughter
chromosomes. As the spindle fibers
attached to the chromosomes
disassemble, each pole receives a set of
daughter chromosomes. The spindle
poles move apart as the unattached
spindle fibers slide past one another. This
contributes to chromosome separation.
Telophase and Cytokinesis
During telophase, the spindle disappears as
new nuclear envelopes form around the
daughter chromosomes. Each nucleus
contains the same number and kinds of
chromosomes as the original parent cell.
Remnants of spindle fibers are still visible
between the two nuclei. Division of the
cytoplasm begins.
(all): © Ed Reschke
Figure 8.6 continued
• Cytokinesis in animal and plant cells
 Accompanies mitosis in most but not all cells
 Mitosis with cytokinesis results in a
multinucleated cell
• Muscle cells in vertebrate animals
• Embryo sac in flowering plants
• Animal cells
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 Cleavage furrow
forms as anaphase
ends
 Contractile ring, band
of actin filaments,
forms a constriction
 Like pulling a
drawstring
cleavage furrow
contractile ring
Figure 8.7 Cytokinesis in animal cells
• Plant cells
 Rigid cell wall prevents furrowing
 Involves building of new plasma membrane and cell walls between
daughter cells
 Golgi apparatus produces vesicles
 Cell plate – newly formed plasma membrane
 New membrane releases molecules that form new plant cell walls
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daughter cells
cell plate formation
daughter nucleus
vesicles containing
membrane components
fusing to form cell plate
nucleoli
daughter
nucleus
© B.A. Palevitz and E.H. Newcomb/BPS/Tom Stack & Associates
Figure 8.8 Cytokinesis in
plant cells
8.4 The Cell Cycle Control System
• Cell cycle must be controlled
• Ensures stages occur in order and
only when the previous stage is
successfully completed
• Cell cycle checkpoints
 3 of the many
• G1 checkpoint
• G2 checkpoint
• Mitotic stage checkpoint
 G1 checkpoint
•
•
•
•
Cell committed to divide after this point
Can enter Go if checkpoint not passed
Proper growth signals must be present to pass
DNA integrity checked – if repair not possible,
apoptosis occurs
 G2 checkpoint
• Verifies DNA replicated
• DNA damage repaired
 Mitotic stage checkpoint
• Between metaphase and anaphase
• All chromosomes must be attached to the spindle
to pass
Figure 8.9 Cell cycle checkpoints
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G1 check point
Apoptosis can occur
if DNA is damaged
beyond repair
G0
G1
M check point
Mitosis stops until
chromosomes
M
are properly
aligned.
G2 chec kpoint
Mitosis will not
occur until DNA
has replicated.
Control
system
G2
S
• Internal and external signals
 Signal – a molecule that stimulates or inhibits an
event
 External signals come from outside the cell
 Internal signals come from inside the cell
 Kinases removes a phosphate from ATP and add it to
other molecules
 S-cyclin must combine with S-kinase for S phase to
occur – DNA replication
 M-cyclin must combine with M-kinase for mitosis to
occur
 Cyclins are present only during certain stages of the
cell cycle
 Destruction of cyclin at the appropriate time is
necessary for normal cell cycle progression
Figure 8.10 Internal signals
of the cell cycle
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S-kinase
S-cyclin
S-cyclin must combine with Skinase for the cell cycle to
begin DNA replication.
• M-cyclin must combine with
M-kinase for the cell cycle to
start mitosis.
G1
M
Control
system
G2
M-kinase
M-cyclin
S
• Cell cycle signals
 External signals
• Epidermal growth factor (EGF) stimulates kin near
an injury to finish cell cycle and repair injury
• Hormone estrogen stimulates lining of the uterus to
divide and prepare for egg implantation
 Contact inhibition – cells stop dividing when
they touch.
 Cells divide about 70 times in culture and then
die
• Due to shortening of telomeres
• Telomere- repeating DNA sequence at end of
chromosome
• Apoptosis
 Programmed cell death
 Remaining cell fragments engulfed by
white blood cells
 Unleashed by internal or external signals
 Helps keep number of cells at
appropriate level
 Normal part of growth and development
• Tadpole tail
• Webbing between human digits
Figure 8.11 Apoptosis
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normal cells
Cell rounds up, and
nucleus collapses.
Chromatin condenses,
and DNA fragments.
DNA
Figure 8.11 Apoptosis continued
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blebs
Plasma membrane
blisters, blebs form.
Cell fragments.
cell fragment
DNA fragment
apoptotic cell
(blebs): Courtesy Klaus Hahn, Cecelia Subauste, and Gary Bikoch from Science Vol. 280, April 3, 1998 p. 32; (apoptotic cell):
Courtesy Douglas R. Green, LaJolla Institute for Allergy and Immunology, San Diego
8.5 Cell Cycle and Cancer
• Cell cycle regulated by signals that inhibit or
promote cell cycle
• Cancer may result from imbalance
• Cancer is a disease of the cell cycle in which
cellular reproduction occurs repeatedly without
end.
• Classified by location
 Carcinoma – cancer of epithelial tissue lining organs
 Sarcoma – cancer arising in muscle or connective
tissue
 Leukemia – cancers of the blood
• Characteristics of cancer cells
 Carcinogenesis – development of
cancer
 Cancer cells…
• Lack differentiation – do not contribute
to body function
 May be immortal – divide repeatedly
• Have abnormal nuclei with abnormal
number of chromosomes
 Cancer cells…
• Do not undergo apoptosis
• Form tumors – do not respond to
inhibitory signals
• Undergo metastasis (cells travel to start
new tumors) and angiogenesis (form
new blood vessels to nourish
themselves)
 Benign – contained within a capsule
 Malignant – invasive and may spread
Figure 8.12 Development of breast cancer
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path of cancer cells
blood
vessel
benign
tumor
malignant
tumor
lymph
vessel
glands
metastatic
tumor
A single cancer cell grows into
a tumor.
The tumor becomes malignant
and invades nearby tissue.
a. Development of breast cancer and metastatic tumors
Cancer cells travel (dotted arrows)
through lymphatic (green) and
blood (red) vessels, and metastatic
tumors form.
Figure 8.12 Development of breast cancer continued
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b. Mammogram showing tumor
© Breast Scanning Unit, Kings College Hospital, London/SPL/Photo Researchers, Inc.
Figure 8.13 Cancer cells
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cancer
cells
• Cancer treatment
 Either remove tumor
or interfere with ability
of cancer cells to
reproduce
 As rapidly dividing
cells, they are
susceptible to
radiation therapy and
chemotherapy
• Damages DNA or
some aspect of
mitosis
• Leads to side effects
normal
cells
© Nancy Kedersha/Immunogen/SPL/Photo Researchers, Inc.
750
 Hormone therapy
designed to prevent
cells from receiving
signals for continued
growth and division
• Prevention of cancer
 Protective behaviors
• Avoid smoking – accounts for about 30% of all
cancer deaths
• Avoid sun exposure – major factor in development
of most dangerous type of skin cancer, melanomas
• Heavy drinkers prone to particular cancers
 Protective diet
• Weight loss can reduce cancer risk
• Increase consumption of foods rich in vitamins A
and C
• Avoid salt-cured or pickled foods
• Include cabbage family members in the diet
Figure 8.14 The right diet helps prevent cancer
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(chard): © Roy Morsch/Corbis; (cabbage, berries, broccoli, oranges): © Corbis RF