lecture04 celldiv mitosis sv2.ppt

8/17/2019 Lecture04 Celldiv Mitosis Sv2.Ppt

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Cell Division and Mitosis

Lecture 4

TOPICS

Prokaryotic cell division

Eukaryotic cell division

Mitosis

PROKARYOTES

BACTERIA and ARCHAEA



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Cell Division

Is what enables the

continuity of life

In prokaryotic cells:

cell division results inreproduction (production

of another cell or another

organism)

In unicellular eukaryotes,

cell division results inreproduction

Prokaryotes Have a Simple Cell Cycle

In bacteria, DNA is a single circular chromosome, located inthe nucleoid region

DNA replication:

– cell elongates, splits into two daughter cells

– division by binary fission

• reproduction may stop under adverse nutritional conditions

Binary Fission:Cell division in

bacteria



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Eukaryotes: Cell Division

a) Amoeba

b) sand dollar

c) dividing bone marrow

cells

• results in genetically

identical daughter cells

Eukaryotic Chromosomes

- each eukaryotic chromosome

consists of a long, linear

DNA molecule, which

carries 100s-1000s of genes

-

proteins maintain structure of

chromosome

- chromatin = DNA + proteins

Chromosome Number Varies Among Species

• humans: 2n = 46

• chimps: 2n = 48

•

elephants: 2n = 56•

dogs: 2n = 72

Walter Flemming’s drawing of

mitosis in a salamander embryo



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Chromosome ReplicationUnreplicated chromosome

Gene 1 Gene 2

The DNA replicates,resulting in two copies ofthe same chromosome..

Gene 1 Gene 2 Replicatedchromosome

Copies of samechromosome Gene 1 Gene 2

Condensedreplicatedchromosome

The DNA condensesaround its associatedproteins, resulting in acompact chromosomethat is 10,000 times shorterthan its original length.

Copies of samechromosome,condensed Centromere

The unreplicated chromosome consists ofa single, long strand of DNA wrappedaround proteins (proteins not shown).

Human Chromosome

sister chromatids

- both contain the identical genetic information

- attached along their length by cohesins (protein complexes)

-

centromere is the region of chromosomal DNA where onechromatid is attached most closely to its sister chromatid

Chromosome Duplication and Cell

Division



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Homologous Chromosomes

A pair of chromosomes that carry genes for…..

Karyotype

•

What type of information does

a karyotype provide?

Chromosomes of a cell

arranged in pairs and

organized by length,

shape, position of

centromere, banding

pattern

Trisomy 21



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Two Types of Nuclear Division Occur in

Many Species

MEIOSIS

Amount of

hereditary materialis reduced by half

Egg SpermGametes

F E R T

I L I Z A T I O N

Normal amount ofhereditary materialis restored

Fertilizedegg

Cell divisionsresponsible for growth(addition of somatic cells)

M I T O S I S

In animals, meiosis occurs priorto production of eggs andsperm

Mitosis: occurs in somatic (non-reproductive) cells

Meiosis: occurs in germ (reproductive) cells

• The complex cell cycle of a eukaryotic cell is composed of

several stages

– G1 phase

– S phase

–

G2 phase

– M phase

– C phase

Interphase

Mitosis

Cytokinesis



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Cytokinesis in Animal and

Plant Cells

- Contractile ring of actin

microfilaments interact with myosin

molecules, causing the ring to contract

- Vescicles from golgi apparatus movealong microtubules to the center of

the cell, producing a cell plate

- Result: 2 daughter cells



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What phase of mitosis is this?

this?

this?this?

this?

Mitosis and Cytokinesis in Action



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MITOSIS (summary)

Function:

Cell Cycle Control System

- consists of

molecules in the

cell that trigger

and coordinate

events in the cell

cycle

Purpose: to

prevent the

division of cells

that are damaged

- if checkpoint

fails, affected cells

can grow out of

control

- uncontrolled cell

division = cancer

The Three Cell-Cycle CheckpointsG2 checkpoint

M

S

G2

G1

Pass this checkpoint if:• chromosome replication

is successfully completed• no DNA damage• activated MPF present

Metaphase checkpoint

Pass this checkpoint if:• all chromosomes areattached to mitotic spindle

Mature cells do notpass this checkpoint(they enter G0 state)

G0

G1 checkpoint

Pass this checkpoint if:• nutrients are sufficient• growth factors (signals from other cells) are present• cell size is adequate• DNA is undamaged



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Cell Cycle Control System

G0, a non-dividing state

Cell Cycle Regulatory Molecules:

1. Protein kinases:

- enzymes that activate other proteins by

phosphorylating them

- provide the go-ahead signals at the G1

and G2 checkpoints

2. cyclin:

- regulatory protein whose concentration

fluctuates in a cell

• to be active, the kinase must attach to a

cyclin, called Cdk

• a) activity of Cdk increases or decreaseswith concentration of cyclin

MPF:

- “maturation promoting factor” is a

Cdk complex (cyclin + Cdk) in the

cytoplasm of M-phase cells

-

thought of as a M-phase promotingfactor because it triggers the cell

past the G2 checkpoint into the M

phase



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Growth factors are proteins released by

certain cells that stimulate other cells to

divide

Platelet-derived growth factor (PDGF)

is needed for the division of fibroblasts- fibroblasts have PDGF receptors on their

plasma membranes

- binding of PDGF molecules to receptors

allows cells to pass G1 checkpoint and

divide

- when any injury occurs, platelets release

PDGF, fibroblasts divide & help heal wounds

Effect of Growth Factors on Cell Division

Stopping Cell Division

density dependent inhibition: phenomenon where crowded cells stop

dividing

anchorage dependence: to divide, cells

must be attached to a substratum

cancer cells: show neither

density-dependent inhibition nor

anchorage dependence



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Cancer: Out-of-Control Cell Division

• Cancer: complex family of diseases caused by cells that

grow in an uncontrolled fashion, that invade nearbytissues, and spread to other sites in the body

• cancers arise from cells in which cell-cycle checkpoints

have failed

Cancer cells:

• that stop dividing do so at random points in the cycle, not

at normal checkpoints

• can divide indefinitely: “immortal”

• by-pass controls that trigger cells to undergo apoptosis

when irreparable mistakes occur

Malignant Breast Tumour

Benign tumour : abnormal cells remain at original site Malignant tumour : cells that spread to new tissues and impair their

functions

Metastasis: spread of cancer cells from original site to distant

locations

Radiation: used to treat …

Chemotherapy: used to treat …

these drugs interfere with specific steps in cell cycle

side effects are due to drug’s effects on normal cells

nausea, hair loss, susceptibility to infection

Karyotype• The chromosomal fingerprint, or karyotype, of a normal human cell (left), includes 46

paired chromosomes. The distinctive karyotype of an aneuploid breast cancer cell (right)includes duplicates of entire chromosomes, missing chromosomes, and chromosome

stubs (Peter Duesberg/UC Berkeley)



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Mitosis

• It is responsible for three key events in multicellular

eukaryotes:

(1) growth

(2) wound repair

(3) cellular division (production of somatic/body cells)

is the basis of ________ reproduction

ASEXUAL REPRODUCTION

• observed in some multi-cellular organisms

• creation of offspring by a

single parent

• offspring are genetically

identical to the parent

ASEXUAL REPRODUCTION

individual reproducing asexually gives rise to a clone

clones:



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Advantages of Asexual Reproduction

Figure 9.17 –Part 1

Figure 9.17 – Part 1

MITOSIS: SUMMARY

lecture04 celldiv mitosis sv2.ppt

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