Transcript Cellular Reproduction

Cellular Reproduction
Why do cells divide and make more
of themselves?
Reasons
• Growth
• Repair
• Asexual Reproduction of Single-Celled
Organisms (Binary Fission)
How do cells divide?
Cell Cycle (Cell Clock)
Interphase
• Most of the time a cell is in Interphase
(90% of time)
– G1 Phase= Cell metabolizes, replicates
organelles, increases in volume
– S Phase= Doubles its DNA
– G2 Phase= Increases more in size, replicates
enzymes and other proteins
Control of Cell Cycle:
Cyclins and Growth Factors
Nucleus
Cytoplasm
Cyclins
• Made in timed fashion and destroyed in
timed fashion
• They bind Cyclin-dependent Kinases
(CdKs)
– Binding activates the CDK
– Kinase phosphorylates and thereby activates
a protein important in the cell cycle
Growth Factors
• Chemicals that bind to cells
and tell cell to activate a
CdK related to cell cycle
1)Cut and bleeding
2) Platelets release
Platelet-derived GF
3) This GF stimulates
skin cells to
divide
What does a cell look like in
Interphase?
Chromatin
M-Phase of Cell Cycle
A) Mitosis (Nucleus Divides)
-Checkpoint to exit Mitosis
B) Cytokinesis (Cytoplasm Divides)
Mitosis steps
1. Prophase=
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Chromatin twists tight and thus thickens and
shortens
Chromatin now appear as Chromosomes
Nucleolus disappears
Nuclear Membrane breaks down
Centriole pairs move to poles of cell
Spindle fibers form out of centrioles and bind
to kinetochore of sister chromatids
Chromosomes
Centromere Region
What does a cell look like in
Prophase?
Asters from
centrosome
regions
Mitosis
2. Metaphase=
• Chromosomes line up at the equator of cell (i.e.. metaphase plate)
• Spindle Fibers are attached to each sister chromatid via kinetochore
on chromatid
What does a cell look like during
Metaphase?
What holds sister chromatids?
• Cohesin Proteins
– Assemble and disassemble in a timed fashion
Mitosis
3. Anaphase=
• Centromere region comes apart
• Sister chromatids pulled away from each
other
• Each sister is now a “daughter
chromosome”
How are sisters pulled?
1) At kinetochore region is a molecular
motor protein that pulls sister along
microtubule (75%)
2) Shortening of microtubules (25%)
What does a cell look like during
Anaphase?
Mitosis
4. Telophase
• Nuclear membranes reform
• Centriole pairs at the extreme poles
• Cleavage furrow or cell plate forms
• Nucleolus reappears in each new cell
• Spindle fibers recede
End of Mitosis (Nuclear Division)
Cytokinesis (Last Part of M Phase)
Animation
• http://www.johnkyrk.com/mitosis.html
Results of M-Phase
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2 daughter cells
Same size as original cell
Genetically and physically like original cell
Same chromosome number as original cell
Mitosis takes about 1-2 hrs
Plant Cell vs. Animal Cell
Cytokinesis
• Plants have no centrioles
• Plants have a cell wall form and NOT a
cleavage furrow
Control of Cell Division
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Cell Anchorage
Cyclins
Density Dependent Inhibition
Growth Factors
Loss of Control
• Cancer
– No Density Dependent Inhibition
– Don’t respond to normal “off” signals
– Uncontrolled replication of cells
– 12 million new cancer victims in 2008 (ACS)
“Cancer” (Latin)
Hippocrates over 2,300 years
ago witnessed long distended
vein growth from breast tumors
Regulation gone:
Regulator Gene Mutations
• Oncogenes (“Gas”)
– Code for proteins that enhance cell division
• Tumor Suppressor Genes (“Brakes”)
– Code for proteins that inhibit cell division
Backup regulation to deal with
mutations
• DNA Self-Repair (DNA Polymerase)
• Apoptosis (Cell Suicide)
• Cells wired not to be able to divide
endlessly
Cancer cells overcome them!
Tumors
• Benign=mass that does not spread but
can create obstructions, can be removed
surgically. Look like normal cells
• Malignant=cancer cells that spread and
set up tumors elsewhere (Metastasis)
– Metastasis cause unclear
– One theory is a cancer WBC hybrid
– Cells look different compared to a normal cell
Types of Cancer
• Carcinoma=body linings ex. skin and
intestine (Melanoma=cancer of
melanocytes)
• Sarcoma=supportive tissue ex. Bone and
muscle
• Leukemias and Lymphomas= bone
marrow, spleen, lymph nodes
• Meningiomas= brain coverings, mostly
benign
Cancer Treatments
• Surgery (1800s)
– Most successful and widely used
• Radiation (Late 1800s)
– Blast and damage cancer cell DNA to initiate
apoptosis
• Chemotherapy (1940s)
– Colchicine, Vinblastin and Taxol: messes up
mitotic spindles
• Immunotherapy
• Nanobot Video
• Natural Killer Cells
Asexual Reproduction
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Takes place by mitotic division
Offspring identical to original cell
Rapid
Large numbers of offspring
Who does it?
– unicellular organisms
– Simple animals
– Plants-sometimes
Methods of Asexual Reproduction
1. Binary Fission
=cell divides
=“daughter cells initially smaller than
original cell but later grow to original’s
size
=done by bacteria, protozoa
• Bacteria replication mov.
• http://www.hhmi.org/biointeractive/media/b
acterial_growth-sm.mov
Methods of Asexual Reproduction
2. Budding
=Mitotic division with unequal Cytokinesis
=parent cell noticeable and larger than its
“bud”
=bud may remain attached or break off
Happens for yeast, hydra, sponges, some
worms
• Yeast
• Hydra Budding
Methods of Asexual Reproduction
3. Spore Formation
– Mitoticly formed
– Produced in large numbers by multicellular
organisms in specialized structures
– Can be covered by a tough coat
– Grows into a multicellular organism
– Done by molds, fungi, algae, protozoa and
sometimes plants
Sporulation
Methods of Asexual Reproduction
4. Regeneration
– Regrowing a body part by mitotic cell division
– Done by Hydra, Planarians, Crabs
Asexual Reproduction in plants
(a.k.a. Vegetative Propagation)
• Developing a whole new plant from a root,
stem or leaf by mitotic divisions of
unspecialized cells
• Can occur naturally or artificially
Natural Vegetative Reproduction
1. Bulbs
– underground stem
– Thick fleshy leaves to store food
– Small bulb sprouts from existing ones and
develop into a whole plant
– Ex. Onions, tulips, lilies
Bulbs
Natural Vegetative Reproduction
2. Corms
– Like a bulb but no fleshy leaves
– Underground stems
– Short and thick
– Stores food
– Ex. Gladioli, crocus, water chestnuts
Corms
3. Tuber
– Large underground stem
– Stores food
– Have “eyes” in surface that sprout new plants
– Ex. potato
Tuber
4. Runner (Stolon)
– Above-ground, horizontal-growing stem
– Has buds that develop into new plants when
buds covered by soil
– Ex. Strawberry
Runners
5. Rhizome
– Horizontal-growing, underground stem
– Thick
– Stores food
– Has Nodes on surface that develop into
vertically-growing stems and roots
– Ex. Ferns, iris, cattails, waterlilies
Artificial Vegetative Propagation
1. Cuttings
– Take stem, leaf or root and put into rooting
hormone powder
– Place in loose soil
– Grows into whole plant
2. Layering
– Bend a plant over on side and cover
segments of its stem with soil
– Covered parts develop into new plants
3. Grafting
– Fusing a branch of one plant onto an existing
plant
– Existing plant=“Stock”
– Fused branch=“Scion”
– Both grow together but also act independently
– Ex. Grafting a lemon branch on an apple tree
– Give lemons and apples
Grafting
Advantages of Artificial Vegetative
Propagation
• Plants all genetically identical-mass
production
• Faster than growing from seed
• Seedless plants can only be kept going by
vegetative reproduction
• Can connect a disease-prone plant to a
disease resistant plant
• Vegetative propagation
• http://wn.com/underground_stem
• Starfish
• starfish eating, starfish eating 2
Meiosis and Sexual Reproduction
• Somatic Cell= body cell (ex. Skin cell)
– A human has 46 chromosomes or 23 PAIRS of
chromosomes
WHY “PAIRS?”
Mom gives:
Dad gives:
22 Autosomes
22 Autosomes
1 sex chromosome
(X)
1 sex chromosome (X or
Y)
Child has:
44 Autosomes
2 Sex Chromosomes
(XX-female or XY-male)
Most of the child’s cells
• Have 23 pairs of Homologous Chromosomes
Homologous chromosomes=
C #2
C #1
C #3
•Chromosomes that look similar
and have the same genetic info
ex. Genes for eye color or hair
color etc.
•Have a Dad version and a Mom
version
•Only chromosome pairs that
don’t look alike are the X and Y
chromosomes
D M
D M
D
M
Karyotype of human male cell after
S-phase of cell division
Diploid vs. Haploid
• Diploid Cell
– Has a mom AND dad version of each chromosome
– 2n
– Most body cells
• Haploid (Monoploid) cell
– Has either a mom OR dad version of each
chromosome
–n
– Gametes (ie. Sperm and Egg)
• Process to make more body cells=Mitosis
• Process to make Gametes=Meiosis
What do we start with to make
gametes?
Oogonium cell in Ovary in Interphase
Spermatogonium cell in Testicle in
Interphase
Meiosis
Prophase I
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Same like Mitosis Prophase except here you
have “Synapsis” and “Crossing-Over” of
homologous pairs of chromosomes
Synapsis
Chiasma
Meiosis
Metaphase I
• Like Mitosis Metaphase but here it’s
Homologous Pairs lining up at equator and
not individual sister chromatids.
Meiosis
• Anaphase I
– Homologous Pairs separate and NOT sister
chromatids
Meiosis
• Telophase I
– 2 daughter cells formed after Cytokinesis
– Each cell is Haploid
– Each human daughter cell at this point would
have 46 chromosomes
Meiosis
• No Interphase
• Each cell begins to divide again
Meiosis
• Prophase II
– Like Prophase of Mitosis
Meiosis
• Metaphase II
– Like Metaphase of Mitosis
– Line up sister chromatids
Meiosis
• Anaphase II
– Like anaphase of Mitosis
– Separate sisters
Meiosis
• Telophase II
– At the end of Cytokinesis there will be 4
Haploid daughter cells
– If human, they will each have 23
chromosomes
Meiosis Timing
• Human Males:
– A month for full meiotic cycle
• Human Females:
– Prophase 1 starts when she is a fetus in the
womb
– Completion of meiosis during puberty
Meiosis and Genetic Diversity
• We have 23 pairs of chromosomes
• In the making of sperm or egg we have:
– 223 (8,388,608) different genetic versions of
gametes
– Add to that variability from crossing over…
– Add to that variability from mutations…
• Meiosis Animation