Mitosis

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Lecture on “Mitosis”

By

• Dasari Sreekanth. M.Sc., NET, TS/AP-SET, GATE, (Ph.D.)

Research scholar,Department of Botany,Osmania university,Email: [email protected]

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Cell Division• An integral part of the cell cycle• Production of genetically identical daughter cells• Cells duplicate their genetic material

– Before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA

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DNA

• Genetic information - genome• Packaged into chromosomes

50 µmFigure 12.3

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• Because of duplication, each condensed chromosome consists of 2 identical chromatids joined by a centromere.

• Each duplicated chromosome contains 2 identical DNA molecules (unless a mutation occurred), one in each chromatid:

Chromosome Duplication

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Two unduplicatedchromosomes

Centromere

Sisterchromatids

Sisterchromatids

Duplication

Non-sisterchromatids

Two duplicated chromosomes

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Chromosome Duplication

0.5 µm

Chromosomeduplication(including DNA synthesis)

Centromere

Separation of sister

chromatids

Sisterchromatids

Centrometers Sister chromatids

A eukaryotic cell has multiplechromosomes, one of which is

represented here. Before duplication, each chromosome

has a single DNA molecule.

Once duplicated, a chromosomeconsists of two sister chromatids

connected at the centromere. Eachchromatid contains a copy of the

DNA molecule.

Mechanical processes separate the sister chromatids into two chromosomes and distribute

them to two daughter cells.

• In preparation for cell division, DNA is replicated and the chromosomes condense

• Each duplicated chromosome has two sister chromatids, which separate during cell division

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chromatin

duplicatedchromosome

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Have your body Have your body changed in the changed in the

pass six pass six months? months?

Tall/WeightTall/Weight

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Are you taller?Are you taller?

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Broken a bone Broken a bone recently?recently?

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Wound – how does Wound – how does your body repair your body repair

itself?itself?

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Mitosis

Mitosis term derived from greek word ‘Mitos’ means thread or fibril.

Parent cell produces two daughter cells. two identical daughter cells that

are genetically identical to the parent cells.

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Mitosis

First observed by ‘Straasburger’ in plant cell (1870).

Boveri and Flemming observed in Animal cell. Term ‘mitosis’ given by- Flemming in 1882. Called also Equational division- due to equal

distribution of chromosomes in daughter nuclei.

Also called as Somatic cell division.

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Q: What kind of cells would perform mitosis?

A: Somatic cells (all body cells except gamete cells)

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Mitosis The sites of mitosis in plants is – meristematic

regions. Root apex Shoot apex Intercalary meristem Lateral meristem Leaves Embryo Seeds.

Intestinal Cell

embryoEpithelial Cell

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Mitosis

In animals; Embryo Skin, bone marrow.

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Mitosis Some haploid & diploid cells divide by mitosis. Each new cell receives one copy of every

chromosome that was present in the original cell. Produces 2 new cells that are both genetically

identical to the original cell.

DNA duplication

during interphase Mitosis

Diploid Cell

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Phases of Mitosis

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Mitosis

The Basic Phases of a Cell’s Life:

I. Karyokinesis.

II. Cytokinesis

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Karyokinesis Nuclear division of parent cell known as karyokinesis. In greek; Karyon= nucleus, kinesis-= movement. Karyokinesis divided into 4 phases;

• Prophase• Metaphase• Anaphase• Telophase

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Prophase

PROPHASE

Early mitoticspindle

AsterCentromere

Chromosome, consistingof two sister chromatids

Prophase can be devided into

Early prophase

Mid prophase

Late prophase.

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Prophase Early Prophase: DNA molecules condensed

and forms short chromosomes.

In this stage chromosomes appear like a ball of wool, so called spireme stage.

In animal cells Centriosome (centriole) divided into two and moves towards opposite pole.

PROPHASE


AsterCentromere


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The Mitotic Spindle apparatus. Also called achromatic figure. Centrioles + aster + spindle fibers = Mototic

spindle apparatus.• The apparatus of microtubules controls

chromosome movement during mitosis• The centrosome replicates, forming two

centrosomes that migrate to opposite ends of the cell

• Assembly of spindle microtubules begins in the centrosome, the microtubule organizing center

• An aster (a radial array of short microtubules) extends from each centrosome.

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Early Prophase:

PROPHASE


AsterCentromere


Centrioles produces out fine microtubular fibrils called Aster rays.

Plants cells do not contain centrioles so called Acentric mitosis.

Animals – centric mitosis.

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Mid Prophase:

PROPHASE


AsterCentromere


Chromosomes shift towards the periphery and leave a clear area.

It becomes shorter and thicker.

Each chromosome consists of two longitudinal threads called chromatids.

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Late Prophase:

PROPHASE


AsterCentromere


Spindle fibers start appearing around the nucleus.

Size of chromosomes is much reduced.

Spindle poles are formed without asters in plants (anastral mitosis).

With asters in animals( astral mitosis).

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Metaphase Metaphase is the longest stage of mitosis, lasting about 20 minutes.

The centrosomes are now at opposite ends of the cell.

The chromosomes arranged on the metaphase plate= congression.

• The chromosomes’ centromeres lie on the metaphase plate.

METAPHASE

Spindle

Metaphaseplate

Centrosome at one spindle pole

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MetaphaseFor each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles.

The entire apparatus of microtubules is called the spindle because of its shape.

This phase is useful for study of chromosomes morphology.

METAPHASE

Spindle

Metaphaseplate

Centrosome at one spindle pole

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The Mitotic Spindle apparatus. Also called achromatic figure. Centrioles + aster + spindle fibers = Mototic

spindle apparatus.• The apparatus of microtubules controls

chromosome movement during mitosis• The centrosome replicates, forming two

centrosomes that migrate to opposite ends of the cell

• Assembly of spindle microtubules begins in the centrosome, the microtubule organizing center

• An aster (a radial array of short microtubules) extends from each centrosome.

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• Some spindle microtubules attach to the kinetochores of chromosomes called= discontinuous micro tubules./ kinetochore micro tubules.

• Some spindle microtubules are not attached to kinetochore called= non kinetochore microtubules or continuous microtubules.

In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell

Microtubules ChromosomesSisterchromatids

AsterCentrosome

Metaphaseplate

Kineto-chores

Kinetochoremicrotubules

0.5 µm

Overlappingnonkinetochoremicrotubules

1 µmCentrosome

The Mitotic Spindle

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Anaphase Anaphase is the shortest stage of mitosis. the centromeres of chromosomes start divide into two. two daughter chromatids are separated. daughter chromatids are migrate towards opposite poles.Spindle fibers are attached to the centromere and pull the chromosomes to the poles.

ANAPHASE

Daughter chromosomes

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ANAPHASE


Anaphaseas their kinetchore microtubules (Discontinuous microtubules ) shorten. Because these microtubules are attached at the centromere region, the chromosomes move centromere first (at about 1 µm/min). The cell elongates as the nonkinetochore microtubules lengthen.By the end of anaphase, two groups of chromosomes are formed, one at each pole.

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ANAPHASE


AnaphaseAnaphasic chromosomes appear as V,L,J,I shaped.

Type of chromosome

Shape Centromere position.

Metacentric V Median

Submetacentric L Submedian

Acrocentric J Sub-terminal

Telocentric I Terminal.

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Telophase

Viscocity of cytoplasm decreases.

Nuclear envelope is formed around each set of chromosomes.

Chromosomes form chromatin. nucleolus is reformed.

Spindle apparatus disappear.• Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.•This phase is just reverse of prophase.

TELOPHASE AND CYTOKINESIS

Nucleolusforming

Cleavagefurrow

Nuclear envelopeforming

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Mitosis in a plant cell

1 Prophase. The chromatinis condensing. The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is staring to from.

Prometaphase.We now see discretechromosomes; each consists of two identical sister chromatids. Laterin prometaphase, the nuclear envelop will fragment.

Metaphase. The spindle is complete,and the chromosomes,attached to microtubulesat their kinetochores, are all at the metaphase plate.

Anaphase. Thechromatids of each chromosome have separated, and the daughter chromosomesare moving to the ends of cell as their kinetochoremicrotubles shorten.

Telophase. Daughternuclei are forming. Meanwhile, cytokinesishas started: The cellplate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell.

2 3 4 5

NucleusNucleolus

ChromosomeChromatinecondensing

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Cytokinesis in animal cell Cleavage of cell into two

halves. In middle region of cell,

microfilaments induces the cell membrane to invaginate.

The furrow forms and deepens centripetally and finally cleaves the parent cell into two daughter cells.

This method is called cleavage method.

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Cytokinesis In Animal And Plant Cells

Daughter cells

Cleavage furrow

Contractile ring of microfilaments

Daughter cells

100 µm1 µmVesicles

forming cell plate

Wall of patent cell Cell plate

New cell wall

(a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (SEM)

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ANIMAL VS. PLANT MITOSIS ANIMAL CELL

Centriole and aster present

Daughter cells separated by cleavage furrow

PLANT CELL No visible

centriole or aster

Daughter cells separated by cell plate

3838

Cell Cycle

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Phase Chromosome Appearance & Location Important Events

Interphase

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

DNA replication, cell grows and replicates organellesNuclear envelope disappears, spindle fibers form

DNA copies itself; chromatin

Chromosomes coil up

Chromosomes line up in the middle

Spindle fibers connect to chromosomes

Chromosome copies divide and move apart

Spindle fibers pull chromosome copies apart to opposite poles

Chromosomes uncoil back into chromatin

Nuclear envelopes reform, 2 new nuclei are formed, spindle fibers disappearDivision of the rest of the cell: cytoplasm and organelles

Chromatin

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Mitosis Application

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Functions of Cell Division

20 µm100 µm 200 µm

(a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM).

(b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM).

(c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).

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Why Is Cell Division Important?

1. All Living Things are made of Cells

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How do little elephants grow up to be BIG elephants?

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The process of asexual reproduction begins

after a sperm fertilizes an egg.

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1. Growth 2. Repair

3. Replacement

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CLONING

• The process to produce genetically identical cells / tissues / organisms / population from the mitosis of a single parent cell (clone)

• Naturally: asexual reproduction, vegetative propagation (plant)

• Artificially: cloning (animal), tissue culture (plant)Why?–Increase quantity –Improve quality –Ensure uniformity of traits

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Controlled Mitosis

• The ability of cell to divide at its own timing and rate• Enables __normal_________ growth and development

and maintenance for perpetuity of living things

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Uncontrolled Mitosis

• If the genes that regulate the cell cycle are damaged or mutated, cell divide __abnormal___cell growth_____

• Cause: – Harmful ray: nuclear radiation, UV ray – Viruses – Carcinogenic chemicals: food additives, benzo (α)

pyrene in cigarette smoke

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The Effects of Uncontrolled Mitosis

• Unregulated and very fast division increase the number of abnormal cells

• Form an abnormal mass – tumour

• Types of tumour: – Malignant

• Invasive by metastasis• Cancer

– Benign• Localize• Does not cause serious

problems • Remove by

___________

What is the treatment of What is the treatment of cancer?cancer?

Brain Brain cancercancer

Breast Breast cancercancer

Mitosis

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