Mitosis and Cell Division

Bio 11 August 31, 2007

Cells are extremely small

• Size limit of cells determined by 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

• Gene- 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

• Chromosomal proteins assist in DNA compaction

• Each chromosome contains different genes

• Chromosomes not always condensed like this

• Chromatin – uncondensed chromosomal DNA

Eukaryotic chromsomes are generally found in pairs

• Chromosomes are organized and numbered by size

• Humans: 2 x 23 homologous pairs of chromosomes = 46 total chromosomes

Chromosome structure

• Decondensed chromosome- chromatin

• After copying, chromosome consists of two sister chromatids, joined at the centromere

• Kinetochore – proteins found on surface of centromere

Each chromosome must be copied before cells can divide

• Called “chromosome” at all stage

• 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

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) – form spindle fibers, and consist (in animal cells) of 2 centrioles

• 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

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

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

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).

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.

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

Figure 8.11A

Figure 8.11B

Figure 8.11C

LE 8-12

Chromosomes

Centromere

Sister chromatids

LE 8-13

Haploid gametes (n 23)

Egg cell

Sperm cell

FertilizationMeiosis

Diploidzygote

(2n 46)

n

Multicellulardiploid adults

(2n 46)

Mitosis anddevelopment

2n

n

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 8-14b

Cleavagefurrow

TELOPHASE PROPHASE METAPHASE ANAPHASE

TELOPHASE

Sister chromatidsseparate

Haploid daughtercells forming

MEIOSIS : Sister chromatids separate

AND CYTOKINESIS AND CYTOKINESIS