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Chapter 10:
How Cells Divide
I. Why do cells Reproduce?
II. Cell Division in Prokaryotes
III. Structure of Chromosomes
IV. Mitosis
V. Cell Cycle Control
I. Why do cells reproduce?I. Why do cells reproduce?
A. Single celled organisms – reproduction of species
B. Multicellular organisms
1. Growth – increase number of cells
2. Maintenance of existing cells
3. Repair of damaged cells
What is Cellular Reproduction?
Enables parent cell to pass on genes & cell components to
daughter cells
Process = cell division
! Different organisms reproduce by different means
! Prokaryotes divide far more simply than Eukaryotes
2
II. Cell Division in Prokaryotes
1. Genetic information = single, circular DNA
2. Prokaryotic cell division = Binary Fission
3. DNA copying is first.
4. Protein ring forms.
5. Septum = cross wall forms.
6. One genome goes to each daughter cell.
7. End Result: 2 genetically identical daughter
cells
1. Replication of DNA
2. Elongation of Cell
3. Formation of FtsZProtein ring
4. Septum Formation byInward growth
5. Cell pinches in two
Daughter Cells
Binary Fission in Prokaryotes
Prokaryote Cell
E. coli ! 20 minutes!
3
DNA: Organized in chromosomes
Accurate passage of genetic info is difficult.
Chromosomes help organize the process.
Remember:
Genes = Code for proteins
Genes = Sequences of nucleotides
= segments of DNA double helix
Chromosome Contains:
DNA double helix
Centromere
Histones: Proteins packaged with
DNA (Chromatin)
centromere
III. Structure of Chromosomes (Eukaryotes)
DNA Organization:
• Chromosomes occur in homologous pairs
• Each homologue is same length and contains same genes
in same order
Diploid: Cells with pairs of homologous
chromosomes (2n)
Haploid: Cells with only one of each type
of chromosome (n = Haploid number)
• Found in sex cells (e.g. sperm / egg)
(Gametes)
• Found in most cells of human body
Karyotype: Entire set of chromosomes
from a single cell
Gene for hair color
4
Eukaryotic chromosomes occur in homologous pairsEukaryotic chromosomes occur in homologous pairs
Humans body cells are
Diploid (2n)
We have 2 of each of 23 types of
chromosomes (n = 23)
= 46 total
Human female Karyotype
Sex
Chromosomes:
X and Y
Female = XX
Male = XY
Organism:
Human
Gorilla
Dog
Cat
Shrimp
Fruitfly
Potato
Ophioglossum
Haploid Number
(n)
23
24
39
19
127
4
24
631
Diploid Number
(2n)
46
48
78
38
254
8
48
1262
5
Replication
Chromosome Chromosome
Replication produces:
Duplicated chromosome
• with 2 chromatids
= sister chromatids
• copies
• remain attached at
centromere
• Packaged with proteins:
Histones
6
Sister Chromatids
Centromere
12
Differing genetic information on homologous chromosomes
Eye-color
genes
Coat-color
genes
ec
EC
White Pink
BlackBrown
HomologousPair
ALLELES: one of two or more alternative states of a gene
LOCUS: the position on a chromosome where a gene is
located
7
1. DNA~25 X106 nucleotidesper chromosome
7. Chromosome
6. Rosettes ofchromatin loops
5. Chromatin loop
Histone
2. Nucleosome(200 nucleotides)
DNA
3. Solenoid30 nm
4. Scaffoldprotein
Eukaryotes:
Two types of cell division:
1. Mitotic Cell Division
2. Meiotic Cell division
• Daughter cells
Identical to parental cell
• Growth, repair &
asexual reproduction
• Daughter cells have !
genetic info of parent
cell
• Sexual reproduction
(Egg & sperm production)
IV. Mitosis
8
Mitotic Cell Division is used for:
1) Growth
IV. Mitosis
2) Maintenance: skin cells
life span = ~ 2 weeks
3) Repair: organ regeneration
liver donation…
Mitosis occurs here !
cells
9
4) Asexual reproduction (by mitotic division):
Offspring are formed from a single parent
clones
• Common in multicellulareukaryotes too
Chandelier
plant
Hydra
•Typical of unicellular eukaryotesParamecium
Eukaryotic cell cycleEukaryotic cell cycle
2 major stages:
1) Interphase (in yellow)
G1: Growth phase 1
(Acquire nutrients, grow)
G1! sensitive to signals
Go to S! Or Go to G0!
Go: Non-dividing
(resting; expression of cell fate)
S: Synthesis of DNA
(chromosomes replicate)
G2: Growth phase 2
(chromosomes condense,
organelles replicate)
*
How does a cell go about
mitotic cell division?
10
Eukaryotic cell cycleEukaryotic cell cycle
2) Cell division
Separation of chromosomes,
Nucleus divides = mitosis
Cytoplasm divides=cytokinesis
Mitosis has 4 main “stages”
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase
2 major stages:
1) Interphase
Eukaryotic cell cycleEukaryotic cell cycle
2 major stages:
1) Interphase (in yellow)
2) Cell division (in blue)
! The cell cycle can vary in
length from minutes to
years
! At any given point, most
cells are in the G0 phase
! Some cells do not divide
(i.e. some muscle, and
nerve cells) and thus stay
in G0 indefinetly
How does a cell go about
mitotic cell division?
11
Mitosis in animal cellsMitosis in animal cells
INTERPHASE (G2)
1. DNA has replicated; started to condense
2. Centrioles replicate (animals only):
microtubule organizing centers
CentriolesAster
Nuclear membraneChromatin (replicated)
Nucleus
First: How do things look at the end of interphase?
12
• Nuclear membrane disintegrates
• Nucleolus disappears
• Chromosomes finish condensing
• Mitotic spindle begins to form and is complete at end of prophase
• Kinetochores form at centromeres and attach to spindle
Centromere and kinetochoreMitotic spindle beginning to form
Chromosomes condensing
MITOSIS: MITOSIS: ProphaseProphase
Kinetochore: a disk of protein
Metaphasechromosome
Kinetochore
Kinetochoremicrotubules
Centromereregion ofchromosome
Chromatid
Spindle Apparatus
Attachment to
Chromosomes
Microtubles are
hollow cylinders
composed of
Tubulin subunits
MITOSIS: MITOSIS: MetaphaseMetaphase
13
ChromosomeCentrioles
Metaphaseplate
Aster
microtubules
Spindle fibers
MITOSIS:MITOSIS:MetaphaseMetaphase
KinetochoreMicrotubules
Polar
Microtubules
Aster
Microtubules
Aster
Microtubules
• The mitotic spindle aligns the chromosomes up at the
metaphase plate (an imaginary plane)
MITOSIS:MITOSIS:AnaphaseAnaphase
Polar microtubules elongate
Kinetochoremicrotubulesshorten,separating sisterchromatids toopposite poles Ana.Ana.
Meta.Meta.
14
• Polar microtubules continue to elongate• Chromosomes reach poles of cell• Kinetochores disappear• Nuclear membrane re-forms• Nucleolus reappears• Chromosomes decondense
MITOSIS:MITOSIS:TelophaseTelophase
Polar
Microtubules
of Spindle
ApparatusChromosomes
Cell plate in plant cells Animal Cells form a
Cleavage furrow
Plant cells: cell plate forms
Animal cells: cleavage furrow forms
CytokinesisCytokinesis
15
Cytokinesis differs between plants and animals
Animals:
• ring of microfilaments “cinches” waist (Cleavage Furrow)
Plants:
• cell plate forms; cellulose delivered via vesicles--> new cell wall
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Cytokinesis in an animal cell
Cleavage
furrow
forms at
the equator
SE
M 1
40!
Daughter cells
Cleavage furrowContracting ring of
microfilaments
Actin Filaments!
16
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin CummingsT
EM
7,5
00!
Cell plate
Daughter
nucleus
Cell wall Cell wall material is deposited
Vesicles containing
cell membrane materialCell plate Daughter cells
Cytokinesis in a plant cell
Fig. 10.15
17
Mitosis in Plant Cells
G2
S G1
C
Spindle checkpointG2 / M checkpoint
G1 / S checkpoint(Start or Restriction Point)
M
Control of the Cell Cycle
V. Cell Cycle Control
At the checkpoints a cell
assesses its internal
state and integrates
external signals
18
Chromosomesattached atmetaphase plate
Replication completed; DNA integrity
Growth factors; Nutritional state of cell; Size of cell
Cdk / G1cyclin
Cdk / G2cyclin (MPF)
G2
S
G1
CM
Spindle checkpoint
G2 / M checkpoint
G1 / S checkpoint
APC
Anaphase Promoting
Complex
Control of the Cell Cycle: Cdk’s
• Kinases are a class of enzyme that
phosphorylate other molecules
• Cdk’s consist of an enzymatic
subunit partnered w/ the protein
cyclin
• Cyclin is a regulatory protein
required to activate Cdk
• Cdk is controlled by the pattern of
phosphorylation (red=off; green=on)
• Cdk’s phosphorylate a number of
targets that result in the synthesis of
proteins required in the cell cycle
• Phosphorylation/Dephosphorylation
is a common theme in cellular
pathways
19
Signal transduction pathway. Example from the G1/S checkpoint.
Fig. 10.22
Growth factor receptor: more per cell in many breast cancers.
Ras protein: activated by mutations in 20–30% of all cancers.
Src kinase: activated by mutations in 2–5% of all cancers.
Rb protein: mutated in 40% of all cancers.
p53 protein: mutated in 50% of all cancers.
Rasprotein
Srckinase
Continue PastCell cycle
checkpoints
Cytoplasm
Nucleus
Rbprotein
p53protein
PROTO-ONCOGENES
TUMOR-SUPPRESSOR GENES
Signal
transduction
pathway
Cyclins & Cyclin-Dependent Kinases
20
Tumor
Single cancer
cell develops
into a tumor
Invade
Neighboring
Tissue
Metastasize
Lymph
vessels
Blood
vessel
Tumors & Metastasis
40
Taxus brevifolia
Interfering with Cell Division
Radiation
Chemotherapy
Pacific Yew - Taxol
Periwinkle - Vinblastin
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