chapter 5.ppt

CHAPTER 5CHAPTER 5

CELL DIVISIONCELL DIVISION

Chapter 5 Cell DivisionChapter 5 Cell DivisionChapter 5 Cell DivisionChapter 5 Cell Division

5.1 Mitosis

Chapter 5 Cell DivisionMitosis

The Necessity for Cell Division in Living Organism

Mitosis is a process of nuclear division which produce two diploid daughter cells, which have the same chromosomal number and are genetically same to parent cell.

Importances of mitosis:produces new cells for growth, repair and replace cells that are dead or damaged in

multicellular organisms.In unicellular organisms, mitosis is a form of asexual

reproduction to increase the number of organisms.

Cell division is divided into two stages:

• Nuclear division

• Cytoplasmic division (Cytokinesis)

Mitosis occur in all somatic cells but not in reproductive cells.

Chromosomal NumberChromosomal NumberHumans have 46 chromosomes (total number of chromosome) which is diploid (2n), 23 from each parent. Every cell (except the reproductive cells) has the same 46 chromosomes

Each species has a characteristic number of chromosomes:

~ corn has 20~ house flies have 10~ chimpanzees have 48.

ChromosomesChromosomes The essential part of a

chromosome is a single very long strand of DNA.

This DNA contains all the

genetic information for creating and running the organism.

The DNA is packaged by proteins bound to it.

At different times, these

proteins cause the DNA to be spread out like spaghetti in a bowl, or tightly condensed into the X-shaped chromosomes we can see under the microscope.

ChromosomesChromosomes

Chromosomes have: Chromatids Centromere

Sister chromatids

ChromosomesChromosomes Before replication,

chromosomes have one chromatid.

After replication, chromosomes

have 2 sister chromatids, held together at the centromere

In mitosis, the two chromatids of each chromosome separate, with each chromatid going into a daughter cell.

Remember that diploid cells have two copies of each chromosome, one from each parent. These pairs of chromosomes are NOT attached together.


The Cell Cycle

Can be divided into two major phases:

M phase (mitosis and cytokinesis)

Interphase

Cell CycleCell Cycle Is the period where the cells Is the period where the cells

are in interphase and in M are in interphase and in M phasephase

Some cells divide Some cells divide constantlyconstantly: : ((cells in the embryo, skin cells in the embryo, skin cells, gut lining cellscells, gut lining cells, etc.) , etc.)

Other cells divide Other cells divide rarely or rarely or nevernever: only to replace : only to replace themselves. themselves.

Actively dividing cells go Actively dividing cells go

through a cycle of events that through a cycle of events that results in mitosis. results in mitosis.

Most of the cycle was called Most of the cycle was called ““interphaseinterphase” (the cell ” (the cell increases in size, but the increases in size, but the chromosomes are invisiblechromosomes are invisible.).)

Cell CycleCell CycleInterphase Interphase

G1 G1 (“Gap or growth phase 1”) (“Gap or growth phase 1”) is the period between mitosis and S, is the period between mitosis and S, when when each chromosome has 1 chromatideach chromosome has 1 chromatid. It is the time when the . It is the time when the cell cell grows grows and performs its normal function. The chromosomes are and performs its normal function. The chromosomes are not not condensed condensed and forms like a and forms like a longlong thread like structure thread like structure called called chromatinchromatin..

The S phaseS phase (“Synthesis”) (“Synthesis”) is the time when the DNA is replicated, when the chromosome goes from having one chromatid to having 2 2 chromatids held together at the centromere.chromatids held together at the centromere.

G2 (Gap or growth phase 2)G2 (Gap or growth phase 2) is the period between S and mitosis. The chromosome have 2 chromatids, and the cell continue to grow cell continue to grow and is getting ready to divideand is getting ready to divide.


InterphaseInterphase

Cell division(Mitosis)

Protein, chloroplast, mitochondria are synthesised

Cell continues to grow and remain metabolically active

Duplication of chromosomes take place.Two identical sister chromatids is formed


4 phases in mitosis

The M Phase

Prophase Metaphase Anaphase Telophase

4 phases in mitosis

The M Phase

Prophase

ProphaseProphase In prophase, the cell In prophase, the cell

begins the process of begins the process of division. division.

1.1. The chromosomes The chromosomes condensecondense (long & thin to (long & thin to shorter & thicker).shorter & thicker).

2.2. The nuclear membrane The nuclear membrane disintegratesdisintegrates and and nucleolus nucleolus disappear.disappear.

3.3. The centrioles move to The centrioles move to opposite poles. During opposite poles. During interphase, the pair of interphase, the pair of centrioles were together centrioles were together just outside the nucleus. just outside the nucleus.

4. The spindle starts to form, growing out of the centrioles towards the chromosomes.

Interphase

Centromere

Chromosomes

Centriole

Sister chromatids

Prophase


Each chromosome consist a pair of sister chromatids attached together at centromere.

Spindle fibres are formed.

Nucleolus and nuclear membrane disappears at the end of prophase.

Centromere

ChromosomesCentriole

Sister chromatids

The M Phase Prophase

MetaphaseMetaphase

Chromosomes line up Chromosomes line up on the equator on the equator (metaphase plate)(metaphase plate) of the of the cell, cell,

with the centrioles at with the centrioles at opposite ends and opposite ends and

the spindle fibers the spindle fibers attached to the attached to the centromeres. centromeres.


The M Phase Metaphase

Metaphase ends when centromeres divide.

Chromosome are lined-up on the cell’s equator.

Mitotic spindle is fully formed.

Spindlefibre

AnaphaseAnaphase In anaphase, the In anaphase, the

centromeres divide. centromeres divide.

At this point, each At this point, each chromosome goes from chromosome goes from having 2 chromatids to having 2 chromatids to being 2 chromosomes, being 2 chromosomes, each with a single each with a single chromatid.chromatid.

Then the spindle fibers contract, and the chromosomes are pulled to opposite poles.


The M Phase Anaphase

Two sister chromatids of each chromosome separate and move to the opposite poles.

Separated chromatids are called daughter chromosomes.

Two poles of cell have equivalent sets of chromosomes at the end of anaphase.

Daughter chromosomes

Pole

TelophaseTelophase The spindle fibers The spindle fibers

disintegratesdisintegrates

The nuclear envelope The nuclear envelope reforms around the two reforms around the two sets of chromosomes.sets of chromosomes.

Daughter nuclei begin to Daughter nuclei begin to reform reform

The cytoplasm divides The cytoplasm divides into 2 separate cells.into 2 separate cells.


The M Phase Telophase

Nucleolus also reproduced in each nucleus.

Two sets of chromosomes reach the opposite poles of the cell.

Spindle fibre disappears.

Nuclear membrane

Cleavage furrow

Cytoplasmic DivisionCytoplasmic Division The organelles (other than the The organelles (other than the

chromosomes) get divided up into chromosomes) get divided up into the 2 daughter cells passively: they the 2 daughter cells passively: they go with whichever cell they find go with whichever cell they find themselves in.themselves in.

Plant and animal cells divide the Plant and animal cells divide the cytoplasm in different ways. cytoplasm in different ways.

In plant cells, a new cell wall made In plant cells, a new cell wall made of cellulose forms between the 2 of cellulose forms between the 2 new nuclei, about where the new nuclei, about where the chromosomes lined up in chromosomes lined up in metaphase. metaphase.

Cytoplasmic DivisionCytoplasmic Division The organelles (other The organelles (other

than the than the chromosomes) get chromosomes) get divided up into the 2 divided up into the 2 daughter cells daughter cells passively: they go with passively: they go with whichever cell they whichever cell they find themselves in.find themselves in.

Plant and animal cells Plant and animal cells divide the cytoplasm in divide the cytoplasm in different ways. different ways.

Cytoplasmic DivisionCytoplasmic Division In plant cells, a In plant cells, a new cell new cell

wall made of cellulose wall made of cellulose forms between the 2 new forms between the 2 new nuclei, about where the nuclei, about where the chromosomes lined up in chromosomes lined up in metaphase. metaphase.

Cell membranes form along the surfaces of this wall.

When the new wall joins with the existing side wall, the 2 cells have become separate.

In animal cells, a ring of actin fibers (microfilaments are composed of actin) forms around the cell equator and contacts, pinching the cell in half. Cleavage furrow is formed.


Cytokinesis

Cytokinesis in a plant cell

Vesicles

Cell wallNuclear envelopePlasma membrane

Growing cell plate

Cytokinesis in animal cell

Cytokinesis

Summary of MitosisSummary of Mitosis Prophase: Prophase:

• Chromosomes condenseChromosomes condense• Nuclear envelope disappearsNuclear envelope disappears• Centrioles move to opposite sides of the cellCentrioles move to opposite sides of the cell• Spindle forms and attaches to centromeres on Spindle forms and attaches to centromeres on

the chromosomesthe chromosomes

MetaphaseMetaphase• Chromosomes lined up on equator of spindleChromosomes lined up on equator of spindle• Centrioles at opposite ends of cellCentrioles at opposite ends of cell

AnaphaseAnaphase• Centromeres divide: each 2-chromatid Centromeres divide: each 2-chromatid

chromosome becomes two 1-chromatid chromosome becomes two 1-chromatid chromosomeschromosomes

• Chromosomes pulled to opposite poles by the Chromosomes pulled to opposite poles by the spindlespindle

TelophaseTelophase• Chromosomes decondenseChromosomes decondense• Nuclear envelope reappearsNuclear envelope reappears• Cytoplasm divided into 2 cellsCytoplasm divided into 2 cells

PLANT vs ANIMALPLANT vs ANIMAL

PLANT CELLPLANT CELL ANIMAL CELLANIMAL CELL

* Cell plate* Cell plate * Cleavage furrow* Cleavage furrow

MITOSIS LABMITOSIS LAB

Animal cell mitosis

MITOSIS LABMITOSIS LAB

Uncontrolled mitosisUncontrolled mitosis

Cancerous cells

A cell

mitosisWithout control

& regulation

What is What is CANCERCANCER ? ?

Cancer is genetic Cancer is genetic disease caused by disease caused by uncontrolled mitosis uncontrolled mitosis due to severe due to severe disruption to the disruption to the mechanism that mechanism that controls the cell controls the cell cyclecycle..

Tumor

Benign Tumor

A cancerous cell divides uncontrollably to form a tumor, an abnormal mass of cells.

Malignant Tumor

TumourTumour


Uncontrolled Mitosis in Living Things

Factor that cause cancer

Radiation Carcinogens Genetic Age

Liver Cancer Tumour

CancerCancer Cancer is a disease of uncontrolled cell division. It

starts with a single cell that loses its control mechanisms due to a genetic mutation. That cell starts dividing without limit, and eventually kills the host.

There are many different forms of cancer, affecting different cell types and working in different ways.

The mutations are caused by radiation, certain chemicals (carcinogens), and various random events during DNA replication.

Cancer ProgressionCancer Progression Once a single cell starts growing

uncontrollably, it forms a tumor, a small mass of cells.

A tumor with a blood supply will grow into a large mass.

Eventually some of the cancer cells will break loose and move through the blood supply to other parts of the body, where they start to multiply.

Cancer TreatmentCancer Treatment Two basic treatments: surgery to remove the tumor, and

radiation or chemicals to kill actively dividing cells.

It is hard to remove all the tumor cells. Tumors often lack sharp boundaries for easy removal, and metastatic tumors can be very small and anywhere in the body.

Radiation and chemotherapy are aimed at killing actively dividing cells, but killing all dividing cells is lethal: you must make new blood cells, skin cells, etc. So treatment must be carefully balanced to avoid killing the patient.

Chemotherapy also has the problem of natural selection within the tumor. If any of the tumor cells are resistant to the chemical, they will survive and multiply. The cancer seems to have disappeared, but it comes back a few years later in a form that is resistant to chemotherapy. Using multiple drugs can decrease the risk of relapse.

Chapter 5 Cell Division

Mitosis

The Application Of Knowledge On Mitosis

Tissue culture (cloning in plant)

Transgenic plants

Cloning in animal

Cell and tissue culture

Plant breeding

Bacteria

DNA extraction and isolation

Cloning and designing genes Transformation

Excised piece of leaf

Isolated cells

Male Body cell taken from

sheep A

DNA extracted

DNA from sheep A fused with egg cell from sheep B

Fused cell develops into embryo which is placed in

uterus of faster mother

Lamb is clone of sheep A

Nucleus removed

Egg cell taken from

sheep BFemale

Advantage : Rate of production and quality of products increased.

Disadvantage : When external environment changes, clones will be destroyed.

What is cloning?

•The process of producing clones or genetically identical copies of cells, tissues or an organism through asexual reproduction.

•There are two types of cloning:

1)Animal cloning

2)Plant cloning


Mitosis

Cloning in animal

Cloning in animal A donor cell is taken from

a sheep’s udder (A)

Donor Nucleus (contain extracted DNA)

These two cells are fused using an electric shock.

Fused Cell

Egg CellThe nucleus of the egg cell is removed

The fused cell begins dividing normally

Embryo

The embryo is placed in the uterus of a surrogate / faster mother

An egg cell is taken from an adult female sheep (B)

Surrogate / Faster Mother(Sheep C)

Cloned Lamb The embryo

develops normally into a lamb-Dolly

Cloning in plants

•Is also known as tissue culture.•Small pieces of root, shoot or stem tissues (explants) are taken from the parent plant.•The explants are sterilized and then placed in a culture medium containing nutrients and growth hormones.•The explants divide by mitosis to form a callus, an undifferentiated mass of tissue.•The callus develops into a somatic embryo.•The embryo develops into a plantlet which can be then transferred to the soil for growth into an adult plant.

Transgenic plants

•Plants that their genes had been altered and engineered to give a high crop yield.

•These plants carry foreign genes that have been introduced into the chromosome.

•So that they have new and beneficial traits. Eg: enhanced growth.

•Transgenic crops such as wheat, soya bean and cotton which are resistance to herbicides, pest and disease have been successfully created by biotechnologist.

Advantages of cloning

~ allows biotechnologist to multiply copies of useful genes or clones.

~ clones can be produced in a shorter time and in large number.

~ creates many transgenic crops which are resistant to herbicides, pests and diseases.

~ cloned plants can produce flowers and fruits within a shorter period, produce better quality yields and delay ripening of fruits for longer shelf life.

~ cloning involves vegetative reproduction which does not need pollinating agents.

Disdvantages of cloning

~ clones does not show any genetic variation.

~ all clones have the same level of resistance towards certain diseases. They are not resistant to new disease or pests.

~ new clones may undergo natural mutations and disrupts the natural equilibrium of an ecosystem.

~ cloned animals have shorter lifespan.

~the long term side effects of using genetically modified organism are not yet known.


5.2 Meiosis

• Meiosis is a cell division (nuclear division) that produces four haploid daughter cells (sperm and ovum / gametes), which have the half chromosomal number than the parent cells and are not genetically identical to each other and to the parent cells.

What is meiosis?

Why Meoisis is Important?

Meiosis is the cell division in the reproductive organs that produces four daughter cells. Eg: gametes

Each gamete contains half the number of chromosomes (haploid) compared to the parent cell (diploid).

Fusion of gametes during fertilization maintains the diploid number in generation.

Daughter cells are genetically different from the parent cells and from each other. This leads to genetic variation in organisms.


Meiosis

MeiosisMeiosis

Occur in reproductive organs and produce four daughter cell.

Human life cycle

Haploid gametes (n=23)

testis

Diploid zygote(2n=46)

Ovum (n)

Sperm (n)

Adults (2n=46)

ovary


Meiosis

Meiosis involves two cycles of nuclear division

Meiosis I Meiosis II

• The number of chromosomes is reduced to half the number of chromosomes of the parent cell.

• Two haploid daughter cells are produced

The haploid cells divide to form four daughter cells called gametes. (division process is like mitosis)


Meiosis

The Stages of Meiosis I

Prophase I

Crossing over occurs at the chiasmata between the non sister chromatids –exchange of genetic material/ segment of DNA

At the end of prophase I, nucleolus disappear and nuclear membrane disintegrates. The centriole replicates and spindle fibres are formed.

Chromosomes

Centromere

Centriole

Chromatids2 Homologouschromosomes

Homologous chromosomes pair together in process called synapsis and form a bivalents OR tetrads.

chiasma

= bivalents/ tetrads

Bivalent / TetradBivalent / Tetrad

2 Homologouschromosomes

chiasmata

= bivalents/ tetrads

Singular: Chiasma Plural: chiasmata


Meiosis

Meiosis

Chiasma

Chiasma where crossing over takes

place


Meiosis


Metaphase I

Chromosomes are lined up side by side as tetrads on the metaphase plate. The chromosomes are still in homologous pairs.

Centromere does not divide.

Spindle fibre

One chromosome of each pair is attached to the spindle fibre from one pole while its homologue is attached to the fibre from opposite pole.


Meiosis


Anaphase I

Homologous chromosomes are pulled by the spindle fibres to opposite poles.

Only two chromosomes (each with two sister chromatids) move towards each pole.

Homologouschromosome


Meiosis


Telophase I

The chromosome arrive at the poles. Spindle fibres disappear.

Each poles has a haploid daughter nucleus.

Cytokinesis is occurs resulting in two haploid daughter cells.

Nuclear membrane

The nuclear membrane and nucleolus reappears.


Meiosis

The Stages of Meiosis II

Prophase II

Spindle fibres reform in each daughter cell.

The nuclear membranes of the daughter cells disintegrate again.

No crossing over takes place// crossing over already happened


Meiosis


Metaphase II

Sister chromatids are positioned randomly on metaphase plate facing opposite poles.

Each sister chromatid is attached to spindle fibres.

Metaphase plate/Equatorial plane


Metaphase II


Meiosis


Anaphase II

Centromers of sister chromatid separate.

Chromosomes are pulled by the shortening of spindle fibre towards the opposite poles.


Meiosis


Telophase II

Nucleoli and nucleus membranes reform.

Spindle fibres break down.

Cytokinesis follows and four haploid daughter cells are formed.


Meiosis

Comparison between Mitosis and Meiosis

Mitosis

In somatic cells (body cells)

Parent cell divides once

Produce two diploid daughter cells

Place occur

Number of division

Number of daughter cells

Meiosis

In reproductive organ

Parent cell divide twice

Produce four haploid daughter

cells

Both processes start from diploid cells. Both processes start from diploid cells.

Both processes are division of cell and nucleus

Both processes are division of cell and nucleus

SimilaritiesSimilarities

Mitosis Meiosis


5.3 Appreciating The Movement Of Chromosomes During Mitosis And Meiosis


Appreciating The Movement Of Chromosomes During Mitosis And Meiosis

Appreciating The Movement Of Chromosomes During Mitosis And Meiosis

Any disruption during mitosis will cause the cells to divide out of control and abnormal cells will be produced.

Number of chromosomes in new organism is maintained as same as parents.

A healthy lifestyle is important to prevent disturbance of cell cycle during mitosis and meiosis.

A healthy lifestyle can be obtained through:

• Have a balanced diet.

• Avoid exposure to carcinogenic substances.

• Practice healthy social activities.

THE END

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