Mitosis and Cell Division
Bio 11 September 5, 2008
Microfilaments differ from microtubules in that microfilaments
A) are larger than microtubules.
B) are found only in plants whereas microtubules are found in plants and animal cells.
C) are mainly composed of actin whereas microtubules are composed of tubulin.
D) help to anchor organelles, whereas microtubules primarily function to help cells change shape and move.
E) form the inner core of cilia and flagella whereas microtubules regulate metabolism
Cell size is determined by physical principles
• Size limit of cells determined by surface area/volume ratio
• Large living things are made of multiple cells
• Living things divide cells in order to grow
Living things are extremely complex
• Cellular machinery is sophisticated and required for life
• Blueprints for all cellular machinery are contained in genes
• Genes are inherited from parents
• Humans have ~30,000 genes
All cells require a copy of the genome
• Genome- all the DNA of the cell
• DNA is similar in all cells• Gene- 1 DNA Molecule (+
proteins the genetic information to produce a single product (protein)
• DNA replication copies all cellular DNA
Prokaryotic genomes consist of a single circular chromsome
• Chromosome- a single molecule of DNA
Prokaryotic cells reproduce by binary fission
1. DNA is copied2. Copies migrate to
opposite ends of cell3. Cell membrane/cell
wall pinches off to form two cells
4. Each daughter cell has exactly the same DNA as the parent cell
Eukaryotic cells have multiple linear chromosomes
• Eukaryotic chromosome = DNA + extra proteins inside nucleus
• Chromosomal proteins assist in DNA compaction
• Each chromosome contains different genes
• Chromosomes not always condensed and visible like this
• Chromatin – uncondensed chromosomal DNA
• In multicelluar organisms, DNA is identical in all cells (Excl. Gametes)
Diploid eukaryotes have chromsomes in pairs
• Karyotype- organized and numbered by size
• Humans: 2 x 23 homologous pairs of chromosomes = 46 total chromosomes
• Each contains ~1000 genes
• 1 or 2 strands per chromosome
Chromosome number does not correlate to complexity
• Oriental Small-clawed Otter 38 • Pea 14 • Pig 38 • Pigeon 80 • Pine Marten 38 • Potato 48 • Rabbit 44 • Raccoon 38 • Radish 18 • Rat 42 • Red Deer (Elk/Wapiti) 68 • Red Fox 38 • Red Panda 36 • Rice 24
• Dog 78 • Wolf 78 • Pigeon 80 • Turkey 82 • Hedgehog Genus Erinaceus
(Woodland hedgehogs) 88 • Hedgehog Genus Atelerix
(African hedgehogs) 90 • Ichthyomys pittieri
(semiaquatic rodent) 94 [highest for a mammmal]
• Carp 104 • Algae 148
Figure 8.3
Chromosome structure
• Decondensed chromosome- chromatin
• After copying, chromosome consists of two sister chromatids, joined at the centromere
• Kinetochore – proteins found on surface of centromere
Figure 8.5
Chromosome structure
Loci(sing:Locus)
Chromosomes look different at different stages of a cell’s life cycle
• Chromatin- uncoiled chromosome
• Not visible at this stage- being used for protein synth.
• Before cell division, strands of DNA are copied
Which one of the following is false?
• A) Prokaryotic chromosomes are more complex than those of eukaryotes.
• B) Most prokaryotes reproduce by binary fission. • C) Prokaryotic cells are generally smaller and simpler
than eukaryotic cells. • D) In prokaryotes, most genes are carried on a circular
DNA molecule. • E) Daughter prokaryotic chromosomes are separated by
some sort of active movement away from each other and the growth of new plasma membrane between them
Each chromosome must be copied before cells can divide
• Called “chromosome” at all stages
• Sister chromatids contain identical DNA
Mitosis vs. Meiosis
• Mitosis – asexual cellular reproduction (somatic cells)– Allows multicellular organisms to grow– Daughter cells are identical to parent cell
• Meiosis – cell division for formation of gametes (eggs and sperm) – Allows sexual reproduction to generate species
diversity– Daughter cells have half the genetic information as
parent cell
The Cell Cycle• G1 – “Growth 1” or “Gap
1” – cell growth• S phase – DNA
synthesis• G2 – interval of rest
before cell division• M – mitosis • Cytokinesis – splitting of
cell contents
• GO – A state of non-division
3. CELL CYCLE~24 hours total
• 1. Interphase - between cell div.• G1 phase - cell growth, ~12 hrs• S phase - synthesize DNA, ~6 hrs• G2 phase - prep. mitosis, ~6 hrs• 2. mitosis - ~half-hour
Prophase, Metaphase, Anaphase, Telophase
• 3. Cytokinesis - ~minutes
LE 8-5
INTERPHASE
G1
G2
S(DNA synthesis)
Cytokinesis
Mito
sis
MITOTICPHASE (M)
Mitosis
• The sorting and separation of chromosomes in nucleus somatic eukaryotic cells during cell division
• Forms 2 identical daughter cells (1/2 size)
• For growth/replacement/healing
• Associated with cancer
• In humans: ~25 million/sec.
• Divided into phases
Phases of Mitosis
• Prophase*• Metaphase• Anaphase• Telophase
* Campbell text adds “prometaphase”
• Interphase – time in between mitotic phases– Normal cell functions (G1+S+G2)
• Cytokinesis- divides cytosol/organelles (creates daughter cells)
Peripheral elements of Mitosis
• Centrosomes (2) – anchors the spindle fibers, and consist (in animal cells) of 2 centrioles each
• Spindle fibers – made of microtubules, they pull apart sister chromatids of chromosomes
LE 8-6a
INTERPHASE PROPHASE PROMETAPHASE
Kinetochore
Fragmentsof nuclearenvelope
CentrosomeEarly mitoticspindleChromatin
Centrosomes(with centriole pairs)
LM
250
Nucleolus Nuclearenvelope
Plasmamembrane
Chromosome, consistingof two sister chromatids
Centromere Spindle microtubules
LE 8-6b
METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS
Metaphaseplate
Spindle Daughterchromosomes
Nuclearenvelopeforming
Cleavagefurrow
Nucleolusforming
Prophase
• mitosis - in most cells (exc. gonads)
• - produces 2 daughter cells
• identical to original but half size
• - for growth + replace., also cancer
• - humans ~25 million/sec.
• Prophase - begins mitosis
• - 2-stranded chromosomes visible
• - nuclear envelope breaks up
• M etaphase - single chromosomes line up at equator
• - carried by spindle (microtubules)
• - centrosome (pairs of centrioles) in animals, anchors the spindle
• A naphase - chromosomes divide between strands
• - 1-stranded chromosomes move to opposite poles of cell
•
• Anaphase - chromosomes divide between strands
• - 1-stranded chromosomes move to opposite poles of cell
•
• Telophase - 2 nuclei form around separate sets of chromosomes
•
• ( Cytokinesis - finishes mitosis )
• - divides cytosol + other organelles
• - results in 2 daughter cells
• ( Interphase - prep. next mitosis )
• - cells return to normal cell activity
• - chromosomes spread as chromatin
• - each 1-stranded chromosome duplicates 2nd strand
Cytokinesis in animal cells is different from plant cells
• Actin and myosin filaments work to contract cell in center
• Cell furrow is formed
Plant cell walls aren’t flexible
• Vesicles containing cellulose form in center of cell
• Fusion of vesicles forms cell plate
• Cell plate forms cell wall of new cells
Cancer, Meiosis, and Mendelian genetics
Mybiology.com
• Chapter 8 Key Concepts quiz- 10 lecture points
• Complete by Tues, 10/14
• >70% correct full credit
• 40-69% correct half credit
Sister chromatids are
A) found right after a cell divides.
B) tightly linked together at a centromere.
C) formed when chromatids separate during cell division.
D) made only of DNA.
E) unique to prokaryotes
Control of the mitotic cycle is criticalG1 checkpoint
G0
G1
G2
G2 checkpoint
M checkpoint
M
S
Controlsystem
External signals can activate or deactivate the cell cycle
• Signals include hormones, growth factors
• Contact inhibition, density inhibition, anchorage dependence are important signals
• If the S phase was eliminated from the cell cycle, the daughter cells would
A) have half the genetic material found in the parental cell.
B) be genetically identical.
C) be genetically identical to the parental cell.
D) synthesize the missing genetic material on their own.
E) None of the choices are correct.
What happens when the system of checkpoints goes awry?
LE 8-8aCells anchor todish surface
and divide.
When cells haveformed a completesingle layer, theystop dividing(density-dependentInhibition).
If some cells arescraped away, theremaining cellsdivide to fill the dishwith a single layerand then stop(density-dependentinhibition).
Mitosis facilitates growth and repairContact- and density- dependent signals tell a cell when to start and stop dividing
LE 8-8aa
Cells anchor todish surfaceand divide.
When cells haveformed a completesingle layer, theystop dividing(density-dependentinhibition).
LE 8-8ab
If some cells arescraped away, theremaining cellsdivide to fill the dishwith a single layerand then stop(density-dependentinhibition).
LE 8-8b
After forming asingle layer,cells havestopped dividing.
Providing anadditional supply ofgrowth factorsstimulatesfurther cell division.
LE 8-10
Tumor
Glandulartissue
Lymphvessels
Blood vessel
A tumor grows from asingle cancer cell.
Cancer cells invadeNeighboring tissue.
Cancer cells spread throughlymph and blood vessels toother parts of the body.
Cancer is unrestricted mitotic cell growth
Metastatic cancer is caused by an accumulation of many errors
• Density-dependent inhibition
• Apoptosis• Cell growth • Nutrient supply
(angiogenesis)• Immune system
evasion
LE 8-10a
Tumor
Glandulartissue
A tumor grows from a single cancer cell.
Cancer cells invadeneighboring tissue.
LE 8-10b
Cancer cells invadeneighboring tissue.
Cancer cells spread throughlymph and blood vessels toother parts of the body.
Lymphvessels
Bloodvessel
DNA damage causes mutations that lead to cancer
• Chromosomes can be repaired, or misrepaired, in a living cell
• Damage to whole chromosomes causes harmful mutations
LE 8-23a
Deletion
Duplication
Inversion
Homologouschromosomes
LE 8-23b
Reciprocaltranslocation
Nonhomologouschromosomes
LE 8-23c
Reciprocaltranslocation
“Philadelphia chromosome”
Activated cancer-causing gene
Chromosome 22
Chromosome 9
• Which one of the following does not occur during mitotic anaphase?
A) The centromeres of each chromosome divide.
B) Sister chromatids separate.
C) The chromatid DNA replicates.
D) Daughter chromosomes begin to move toward opposite poles of the cell.
E) All of the choices occur during mitotic anaphase.
Figure 8.11A
Figure 8.11B
Meiosis
Asexual Reproduction is a primary means of propagation for many species
Sexual reproduction generates diversity
• Variety in offspring improves chances of adaptation to changing environments
The offspring of sexual reproduction inherit parental
traits• Offspring inherit
DNA from each parent
• Offspring are not the same
• DNA is from the same source
LE 8-13
Haploid gametes (n 23)
Egg cell
Sperm cell
FertilizationMeiosis
Diploidzygote
(2n 46)
n
Multicellulardiploid adults
(2n 46)
Mitosis anddevelopment
2n
nMeiosis is the process of cell division that allows gamete formationGametes are haploid (n), somatic cells are diploid (2n)
Chromosomes come in pairs
• For diploid organims (2n)
• One chromosome in a paired set comes from each parent
• #’s 1-22 are autosomes
• X and Y are sex chromosomes
LE 8-12
Homologous Chromosomes
Centromere
Sister chromatids
Homologous chromosomes• Pairs of
chromosomes are homologous
• The site for particular genes are called loci (singular: locus)
• Identical strands of the same chromosome are sister chromatids
Loci
LE 13-6
Key
HaploidDiploid
Gametesn
Diploidmulticellularorganism(sporophyte)
MitosisDiploidmulticellular
organism
FERTILIZATIONMEIOSIS
Zygote
n
n
2n 2n
Animals Plants and some algae Most fungi and some protists
n n
n
n n
nn
n
n
nFERTILIZATION
FERTILIZATION
MEIOSIS
MEIOSIS
Gametes Gametes
Zygote
ZygoteMitosis
Mitosis Mitosis Mitosis Mitosis
2n2n
2n
Spores
Haploid multicellular organism (gametophyte)
Haploid multicellular organism
Overview of Meiosis
• Meiosis consists of 2 major stages, Meiosis I and Meiosis II
• Cell copies DNA once, divides twice, creating 4 haploid cells
• In meiosis I, homologous pairs of chromosomes are grouped, recombined, and then segregated into two intermediate cells
• In meiosis II, those cells are divided
The Stages of Meiosis
• In (meiosis I), homologous chromosomes separate
• Meiosis I results in two haploid daughter cells with replicated chromosomes
• In the second cell division (meiosis II), sister chromatids separate
• Meiosis II results in four haploid daughter cells with unreplicated chromosomes
LE 8-14a
INTERPHASE PROPHASE METAPHASE ANAPHASE
MEIOSIS
Centrosomes(with centriolepairs)
Sites of crossing over
Spindle
Microtubulesattached tokinetochore
Metaphaseplate
Sister chromatidsremain attached
Homologouschromosomes separate
Centromere(with kinetochore)
TetradSisterchromatidsChromatin
Nuclearenvelope
: Homologous chromosome separate
LE 13-8aa
Centrosomes(with centriole pairs)
Nuclearenvelope
Chromatin
Chromosomes duplicate
INTERPHASE
MEIOSIS I: Separates homologous chromosomes
METAPHASE I ANAPHASE I
(Interphase precedes meiosis, of course)
• Division in meiosis I occurs in four phases:Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase I• >90% of the time required for
meiosis• Chromosomes condense• Synapsis: homologous
chromosomes pair up• Crossing over: nonsister
chromatids exchange DNA segments
• Tetrad: four chromatids• Chiasmata: X-shaped regions
where crossing over occurred
Crossing-Over in Prophase I
Crossing-over in Prophase I
LE 13-8ab
Sisterchromatids
Chiasmata
Spindle
Centromere(with kinetochore)
Metaphaseplate
Homologouschromosomesseparate
Sister chromatidsremain attached
Microtubuleattached tokinetochore
Tetrad
MEIOSIS I: Separates homologous chromosomes
PROPHASE I METAPHASE I ANAPHASE I
Homologous chromosomes (red and blue) pair andexchange segments; 2n = 6in this example
Pairs of homologouschromosomes split up
Tetrads line up
Metaphase I
• Tetrads line up at the metaphase plate
• Microtubules from one pole are attached
• Microtubules from the other pole are attached to the kinetochore of the other chromosome
Animation: Metaphase IAnimation: Metaphase I
Independent Assortment in Metaphase I
• Random alignment of maternal/paternal chromosomes at the metaphase plate
• Produces genetic variability within populations
Independent Assortment in Metaphase I
Independent Assortment in Metaphase I
Independent Assortment of Chromosomes
• Homologous pairs of chromosomes orient randomly at metaphase I of meiosis
• Each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs
• The number of combinations possible when chromosomes assort independently into gametes is 2n-1, where n is the haploid number
• For humans (n = 23), there are more than 8 million (222) possible combinations of chromosomes
LE 13-8ab
Sisterchromatids
Chiasmata
Spindle
Centromere(with kinetochore)
Metaphaseplate
Homologouschromosomesseparate
Sister chromatidsremain attached
Microtubuleattached tokinetochore
Tetrad
MEIOSIS I: Separates homologous chromosomes
PROPHASE I METAPHASE I ANAPHASE I
Homologous chromosomes (red and blue) pair andexchange segments; 2n = 6in this example
Pairs of homologouschromosomes split up
Tetrads line up
Anaphase I
• homologous chromosomes separate
• One chromosome moves toward each pole
• Sister chromatids remain attached at the centromere
LE 8-14b
Cleavagefurrow
TELOPHASE PROPHASE METAPHASE ANAPHASE
TELOPHASE
Sister chromatidsseparate
Haploid daughtercells forming
MEIOSIS : Sister chromatids separate
AND CYTOKINESIS AND CYTOKINESIS