Transcript Power Point Honors Cell Division

Ch. 8 Cell Reproduction
Why do cells make new cells?
1. Growth
2. Maintenance – cells wear out
3. Repair - injury
4. Regeneration – lost body part
5. Reproduce asexually
8.1 Some organisms
reproduce asexually
• Offspring are
genetic copies of
the parent and of
each other
Figure 8.1A
– All organisms can reproduce sexually
• Creating variety in the offspring
Figure 8.1B
8.3 Prokaryotes
reproduce by binary
fission
• One chromosome
• Chromosome copies itself
• Cell lengthens,
copies move apart
• Cell membrane
divides cell in two
• Two identical organisms
Eukaryotic nuclei contain many
chromosomes
Each chromosome contains thousands of genes
- must be organized before cell can dividing
Prokaryotic chromosomes
LM 340
Colorized
TEM
32,500
One-celled protists also do fission, but
must do mitosis first to divide
chromosomes evenly
8.5 The cell cycle - two phases
Interphase
– most of cell life
- non-dividing cell
INTERPHASE
G1
S
(DNA synthesis)
G2
Mitotic (M) phase – dividing cell
Figure 8.5
Cell Cycle
INTERPHASE
G1  growth, normal life functions
S  “synthesis” – DNA replicates
G2  final growth; prepares to divide
MITOTIC PHASE
Mitosis – chromosomes condense, organize and divide
- each new cell gets one copy of every chromosome
Cytokinesis – cytoplasm divides
Some cells divide often
Tissues contain cells that are less specialized
embryo
Embryo
Blood stem cells
Plants and simple organisms
Plants, simple animals
Digestive lining
cells
Skin
cells
Bone marrow stem cells Digestive lining cells
Some divide rarely or not at all
Highly specialized cells do not divide when mature
Nerve cells
Nerve cells
Muscle cells
Muscle
Liver cells
–cells
when injured
Cartilage or tendon cells
Cartilage, tendons
How do muscles get bigger if
muscle cells don’t divide?
• Made of muscle fibers
• Fibers are made of many fibrils
Muscle fibers make muscle tissue
Muscles get bigger when fibers enlarge
• Exercise makes tiny tears in muscle fibers
• As they heal, extra proteins make the fibers get
thicker  muscles get bigger
AND cells can make more fibers
Muscle tears heal with collagen
and scar tissue
DNA
Review structure:
Nucleotides
Deoxyribose
Phosphate
Bases A C T G
Polymers
Genetic code
Watson and Crick, 1953
Ch.10 Chromosomes of eukaryotes
duplicate in cell division
Before cell divides - DNA replicates
a. Helicase “unzips” molecule
b. Original strands are templates
c. Free nucleotides in nucleus
d. Polymerase – base-pairing rules
 two identical molecules
Semi-conservative replication
• Original strands serve as templates
• New molecules have one original strand
and one new strand
Eukaryotic chromosomes
Nucleus in
non-dividing cell
Early mitosis
Chromosome is in
CHROMATIN form
CHROMATIN begins
to condense before a
cell can divide
BEFORE a cell divides
DNA condensation
•DNA is ALREADY COPIED (replicated)
•coils, packs, condenses  Forms dense “CHROMOSOMES”
•keeps copies organized and intact until cell splits
CHROMOSOMES CONDENSE
BEFORE CELL DIVISION
Nucleosomes
group to form
chromatin
DNA
DNA wraps
around histone
proteins
Groups of
histones form
nucleosomes
This coils and
wraps until it all fits
into the nucleus.
One chromosome
(copied and packed
for cell division)
SEM of human
chromosomes
Sister chromatids
identical copies
Centromere
holds chromatids
together
Prokaryotes have a single, circular
chromosome, no histones; no nucleus
Double-stranded
(replicated)
chromosome
Replicated, condensed chromosome
When a cell begins to divide
Microtubules form
spindle fibers
between the
centrioles
Spindle fibers form
a star shape at
centrioles (aster)
Centrioles move toward
opposite poles of the
cell
Chromatin begins
to condense
PHASES OF MITOSIS
PROPHASE – cell organizes, prepares
•chromatin
•nuclear membrane, nucleolus
•spindle and asters
•centrioles
PROMETAPHASE – chromosomes condensed
•move toward middle
•centrioles to opposite poles
•spindle
METAPHASE – chromosomes in middle
•Centromeres and spindle fibers
LM 250
– The stages of cell division
INTERPHASE
PROPHASE
Centrosomes
(with centriole pairs)
Chromatin
Early mitotic
spindle
PROMETAPHASE
Centrosome
Fragments
of nuclear
envelope
Kinetochore
Nucleolus
Nuclear
envelope
Figure 8.6 (Part 1)
Chromosome, consisting
Plasma
membrane ot two sister chromatids
Centromere
Spindle
microtubules
ANAPHASE -chromosomes separate
• spindle fibers pull
• single copies to opposite poles of cell
TELOPHASE – return to normal
• chromosomes relax/uncoil into chromatin
• nuclear membranes form; nucleoli appear
• spindle fibers disappear
CYTOKINESIS - division of cytoplasm
•
identical daughter cells
Cleavage furrow
ANAPHASE
METAPHASE
Cleavage
furrow
Metaphase
plate
Spindle
Figure 8.6 (Part 2)
TELOPHASE AND CYTOKINESIS
Daughter
chromosomes
Nuclear
envelope
forming
Nucleolus
forming
Cell division differs for plant and animal cells
8.7 Animal cytokinesis
• Microfilaments
SEM 140
• Cleavage furrow
Cleavage
furrow
• Pinch cytoplasm in two
Cleavage furrow
Contracting
ring of
microfilaments
Daughter cells
Figure 8.7A
Cell plate
forming
Wall of
parent cell
Daughter
nucleus
In plants
- no centrioles or asters
TEM 7,500
(has spindle)
- cell plate forms
- new cell wall grows
Cell wall
New cell wall
along sides of cell plate
Vesicles containing
cell wall material
Figure 8.7B
Cell plate
Daughter cells
Plant, Animal Mitosis
Animal cells:
- centrioles anchor spindle fibers
- asters visible at centrosomes
- microfilaments pinch cytoplasm
Plant cells:
- no centrioles or asters
- cell plate forms to divide cytoplasm
Plant cell mitosis
Animal cell mitosis
Plant cell mitosis
Control of Cell Division
Chemical signals tell a cell when to divide
Some made by cell; some from cell environment
Normal rate: growth, repair
- asexual reproduction in some organisms
Slow rate: some cell types divide rarely (liver)
- aging  slow healing, lose some cells
Fast rate: some cell types (skin, digestive lining)
- embryo, growing zones (bones, root tips)
Uncontrolled  cancer
As tissues age, cell division slows
Some worn-out cells are not replaced
Tissue cells gradually decrease in number
Growth factors
• Proteins secreted by cells, can start or stop cell division
• When cells crowded, growth factors used up
 stop dividing
After forming a
single layer,
cells have
stopped dividing.
Providing an
additional supply of
growth factors
stimulates
further cell division.
Figure 8.8B
Cyclins
- proteins produced by cell at constant rate
- when reach high level, cell divides
Programmed Cell Death
apoptosis
1. Cells damaged too much to repair
– self-destruct
2. Embryonic development – lose unneeded cells
Checkpoints in cell cycle
Anchorage and Contact Inhibition
Anchored to a solid substance
- ex. Extracellular matrix,
collagen framework
Contact: stop dividing when
they touch other cells
- density-dependent inhibition
Figure 8.8A
Cells anchor to
dish surface
and divide.
When cells have
formed a complete
single layer, they
stop dividing (densitydependent inhibition).
If some cells are
scraped away, the
remaining cells divide
to fill the dish with a
single layer and then
stop (density-dependent
inhibition).
8.10 Cancer – uncontrolled cell division
• Cancer cells ignore cycle controls
– Repeated and rapid cell divisions; immortal
• tumor – mass of non-functioning cells
– Benign – not cancer; do not spread to nearby tissue
– May get large enough to stop tissue function
• Malignant tumor – cancer
– Will invade and destroy neighboring tissue
• Metastatic tumor – spreads to other body parts
– Starts new cancers
Cells look abnormal and do not respond to
signals that control the cell cycle
• If not treated early, cancer will spread
• kills by destroying organ function
Lymph
vessels
Tumor
Blood
vessel
Glandular
tissue
A tumor grows from a
single cancer cell.
Figure 8.10
Cancer cells invade
neighboring tissue.
Cancer cells spread through
lymph and blood vessels to
other parts of the body.
Cancer – uncontrolled cell division
1) DNA damage - Cells begin to divide abnormally
2) Keep dividing, invade healthy tissue (malignant)
3) Spread in blood or lymph, can start new tumors
(metastatic)
BE CAREFUL when sunning
• Wear sunscreen, sunglasses
• Avoid brightest part of the day
• Don’t use tanning beds
The most common cancer - skin
Melanoma -deadliest
Melanoma
Basal cell
Squamous Cell
Cancer treatment
Radiation – high-energy, carefully aimed at tumor
Chemotherapy – drugs specific for tumor types
• interfere with cell division
• some normal cells destroyed, too
– Skin (lose hair); digestive lining (nausea)
Surgery – remove tumor and nearby cells
Boost immune system – healthy diet, reduce stress
Asexual Reproduction
New organism from one parent
– offspring identical genetically
Advantages:
1) no mate – good for solitary, sessile organisms
or when population density is low
2) continues a successful gene makeup
3) usually fast, large numbers
Disadvantage: no genetic variation
Forms of Asexual Reproduction
1) Binary Fission
- bacteria, protists
2) BUDDING
- small growth from
unspecialized cells
- hydra, sponges
- yeast (unicellular)
- some plants
Budding - Asexual Reproduction
LM 10
Hydra with bud
Budding cacti
3) Spore formation
Spores – tiny cells with
genetic material
- many
- disperse from parent
- mosses, ferns, fungi
4) Vegetative propagation
Complete plant can grow from part of parent plant
Vegetative – root, stem, or leaf
Natural Methods
Runners
Bulbs
Tubers and
Underground Stems
Artificial Vegetative Propagation
Root Separation
Cuttings
Grafting
5) Regeneration – replace lost body part
starfish can replace an arm
Lizards can replace a tail
flatworms can regrow a body
Stem cells and differentiation
Differentiate – cells specialize as embryo develops
Stem cell – unspecialized cell
- can differentiate to form many kinds of cells
- depends on chemical signals from nearby cells
Multipotent or totipotent
Stem cells for cloning tissues