Download I. Why do cells reproduce?

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?
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
1
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
Binary Fission in Prokaryotes
1. Replication of DNA
Prokaryote Cell
2. Elongation of Cell
3. Formation of FtsZ
Protein ring
4. Septum Formation by
Inward growth
5. Cell pinches in two
Daughter Cells
E. coli ! 20 minutes!
2
III. Structure of Chromosomes (Eukaryotes)
DNA: Organized in chromosomes
Accurate passage of genetic info is difficult.
Chromosomes help organize the process.
Remember:
centromere
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)
DNA Organization:
• Chromosomes occur in homologous pairs
• Each homologue is same length and contains same genes
in same order Gene for hair color
Diploid: Cells with pairs of homologous
chromosomes (2n)
• Found in most cells of human body
Haploid: Cells with only one of each type
of chromosome (n = Haploid number)
• Found in sex cells (e.g. sperm / egg)
(Gametes)
Karyotype: Entire set of chromosomes
from a single cell
3
Eukaryotic 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
Sex
Chromosomes:
X and Y
Human female Karyotype
Female = XX
Male = XY
Haploid Number
Diploid Number
Organism:
(n)
(2n)
Human
Gorilla
23
24
46
48
Dog
Cat
39
19
78
38
Shrimp
127
254
Fruitfly
4
8
Potato
Ophioglossum
24
631
48
1262
4
Replication produces:
Duplicated chromosome
Chromosome
Chromosome
• with 2 chromatids
= sister chromatids
•
copies
•
remain attached at
centromere
Replication
• Packaged with proteins:
Histones
5
Sister Chromatids
Centromere
Differing genetic information on homologous chromosomes
Coat-color
genes
Eye-color
genes
Brown
Black
C
E
c
e
Homologous
Pair
White
Pink
ALLELES: one of two or more alternative states of a gene
LOCUS: the position on a chromosome where a gene is
located
12
6
4. Scaffold
protein
5. Chromatin loop
nm
30
3. Solenoid
DNA
6. Rosettes of
chromatin loops
7. Chromosome
Histone
2. Nucleosome
(200 nucleotides)
1. DNA
~25 X106 nucleotides
per chromosome
IV. Mitosis
Eukaryotes:
Two types of cell division:
1. Mitotic Cell Division
• Daughter cells
Identical to parental cell
• Growth, repair &
asexual reproduction
2. Meiotic Cell division
• Daughter cells have !
genetic info of parent
cell
• Sexual reproduction
(Egg & sperm production)
7
IV. Mitosis
Mitotic Cell Division is used for:
1) Growth
2) Maintenance: skin cells
life span = ~ 2 weeks
cells
Mitosis occurs here !
3) Repair: organ regeneration
liver donation…
8
4) Asexual reproduction (by mitotic division):
Offspring are formed from a single parent
clones
•Typical of unicellular eukaryotes
Paramecium
Chandelier
plant
• Common in multicellular
eukaryotes too
Hydra
How does a cell go about
mitotic cell division?
Eukaryotic 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)
9
Eukaryotic cell cycle
2 major stages:
1) Interphase
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
How does a cell go about
mitotic cell division?
Eukaryotic 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
10
Mitosis in animal cells
First: How do things look at the end of interphase?
INTERPHASE (G2)
Nucleus
Nuclear membrane
Chromatin (replicated)
Centrioles
Aster
1. DNA has replicated; started to condense
2. Centrioles replicate (animals only):
microtubule organizing centers
11
MITOSIS: Prophase
Kinetochore: a disk of protein
Chromosomes condensing
Mitotic spindle beginning to form
Centromere and kinetochore
• 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
MITOSIS: Metaphase
Chromatid
Spindle Apparatus
Attachment to
Chromosomes
Kinetochore
Kinetochore
microtubules
Microtubles are
hollow cylinders
composed of
Tubulin subunits
Centromere
region of
chromosome
Metaphase
chromosome
12
MITOSIS:
Metaphase
Centrioles
Chromosome
Aster
Microtubules
Aster
microtubules
Metaphase
plate
Spindle fibers
Kinetochore
Microtubules
Polar
Microtubules
Aster
Microtubules
• The mitotic spindle aligns the chromosomes up at the
metaphase plate (an imaginary plane)
MITOSIS:
Anaphase
Polar microtubules
elongate
Kinetochore
microtubules
shorten,
separating sister
chromatids to
opposite poles
Meta.
Ana.
13
MITOSIS:
Telophase
Chromosomes
Polar
Microtubules
of Spindle
Apparatus
• Polar microtubules continue to elongate
• Chromosomes reach poles of cell
• Kinetochores disappear
• Nuclear membrane re-forms
• Nucleolus reappears
• Chromosomes decondense
Cytokinesis
Animal Cells form a
Cell plate in plant cells
Cleavage furrow
Plant cells: cell plate forms
Animal cells: cleavage furrow forms
14
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
Cytokinesis in an animal cell
Cleavage furrow
SEM 140!
Cleavage
furrow
forms at
the equator
Contracting ring of
microfilaments
Actin Filaments!
Daughter cells
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
15
Cytokinesis in a plant cell
Cell plate
TEM 7,500!
Daughter
nucleus
Cell wall
Vesicles containing
cell membrane material
Cell plate
Cell wall material is deposited
Daughter cells
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Fig. 10.15
16
Mitosis in Plant Cells
V. Cell Cycle Control
G2 / M checkpoint
Spindle checkpoint
M
C
G2
Control of the Cell Cycle
S
At the checkpoints a cell
assesses its internal
state and integrates
external signals
G1
G1 / S checkpoint
(Start or Restriction Point)
17
Chromosomes
attached at
metaphase plate
Replication
completed;
DNA integrity
Cdk / G2 M
cyclin (MPF)
Anaphase Promoting
Complex
APC
C
G2
Spindle checkpoint
G2 / M checkpoint
G1 / S checkpoint
S
G1
Cdk / G1
cyclin
Growth factors;
Nutritional state of cell;
Size of cell
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
18
Signal transduction pathway. Example from the G1/S checkpoint.
Fig. 10.22
PROTO-ONCOGENES
Growth factor receptor:
more per cell in many
breast cancers.
Ras
Signal
protein
transduction
pathway
Src
kinase
Cytoplasm
Rb
protein
Nucleus
p53
protein
Cyclins & CyclinDependent Kinases
Ras protein:
activated by mutations
in 20–30% of all cancers.
Src kinase:
activated by mutations
in 2–5% of all cancers.
TUMOR-SUPPRESSOR GENES
Rb protein:
mutated in 40% of all
cancers.
p53 protein:
Continue Past
Cell cycle
checkpoints
mutated in 50% of all
cancers.
19
Tumors & Metastasis
Tumor
Single cancer
cell develops
into a tumor
Lymph
vessels
Blood
vessel
Invade
Neighboring
Tissue
Metastasize
Interfering with Cell Division
Radiation
Chemotherapy
Periwinkle - Vinblastin
Pacific Yew - Taxol
Taxus brevifolia
40
20
END Mitosis
1.
What is the difference between chromatin and
chromatids?
2. If a diploid mother cell had 24 chromosomes, how
many chromosomes would each daughter cell have
after mitosis?
After meiosis?
3. What is the product of “replication”?
42
21