Cell division 1

Edited by: Hasimah Azit

CELL DIVISION FUNCTIONS IS to:

Produce new cells for: reproduction – gamete growth – new cells and repair – replace dead

cells

Basic definitions

gene - basic unit of heredity; codes for a specific trait

somatic cell - all body cells except reproductive cells

gamete - reproductive cells (i.e. sperm & eggs) chromosome - elongate cellular structure

composed of DNA and protein

diploid (2n) - cellular condition where each chromosome type is represented by two homologous chromosomes

haploid (n) - cellular condition where each chromosome type is represented by only one chromosome

chromatid - one of two duplicated chromosomes connected at the centromere

centromere - region of chromosome where microtubules attach during mitosis and meiosis

Basic definitions

Cell division involves

the distribution of identical genetic material, DNA

to two daughter’s cells.

2n

2n

2n

twoidenticaldaughtercells

The Cell Cycle

Cell CycleCell Cycle

The dividingdividing and non-dividingnon-dividing stages in the life of a cell.

Phases:

1.1. InterphaseInterphase: growth and DNA replication

2.2. ProphaseProphase

3.3. MetaphaseMetaphase

4.4. AnaphaseAnaphase

5.5. TelophaseTelophase

6. Cytokinesis – 6. Cytokinesis – cytoplasm dividedcytoplasm divided

Mitotic divisionMitotic division

InterphaseInterphase

1. 1. GG11 (gap) phase: (gap) phase:

a. grow into matured size and protein is synthesizedb. most cell are arrested in this phasemost cell are arrested in this phase.

2. 2. S phase:S phase:a. DNA replication DNA replication takes place.

3. 3. GG22 (gap) phase: (gap) phase:

a. Cellular growth and energy and organelles preparation for M phaseM phase.

MitosisMitosis

The form of cell divisioncell division by which a somatic somatic cell cell duplicates.

MitosisMitosis is asexual reproduction.asexual reproduction.

Cell division Cell division is the continuation of life based on the reproduction of cells.

mitosis - nuclear/chemical events resulting in two daughter nuclei which have identical genetic material to each other and to the mother cell

cytokinesis - division of the cytoplasm.

Mitosis division Mitosis division

Look at the section through the tip of an onion root tip and try to recognize:

* dividing cells – mitotic cells

* elongated cells

Onion root tip

Mitotic cellsElongated cells

InterphaseInterphase

NucleusNucleus and nucleolusnucleolus visible.

Nuclear membrane

nucleolus

cell membrane

chromatin

A chromosomechromosome is made up of a DNADNA

ChromatinChromatin is a long, thin fiber that is folded and coiled (invisible).

chromosome

Duplication of chromosome – from single strand to double strand

Chromosome replicationChromosome replication

A replicated chromosomechromosome consist of two strands of identical chromosomal material called chromatidschromatids (sister chromatidssister chromatids).

chromatid

chromatid

S phase: chromosomes replicate

chromosome

chromosome

centromere

A chromatidchromatid is a chromatidchromatid as long as it is held in association with a sistersister chromatidchromatid at the centromerecentromere.

chromatid

chromatid

centromere

chromosome

ChromatidChromatid

ProphaseProphase

Longest phaseLongest phase

Nucleolus disappears

Chromatin material condenses into chromosomeschromosomes, consisting of two sister chromatidssister chromatids.

ProphaseProphase

CentriolesCentrioles move apart (not found in plants).

Spindle fibers Spindle fibers form and attach from centriolescentrioles to centromeres centromeres

Nuclear envelope fragments and disappears.

ProphaseProphase

late prophaselate prophaseearly prophaseearly prophase

centrioles

spindle fibers

centromere

nuclear envelopedisappearing

asterfibers

Find the stages in the picture below

MetaphaseMetaphase

Shortest phase

CentriolesCentrioles are at opposite ends of the cell and attached with aster fibersaster fibers.

ChromosomesChromosomes move to the metaphase platemetaphase plate (equatorial plateequatorial plate - center of cell).

MetaphaseMetaphase

metaphase plate

centrioles

spindle fibers

asterfibers

AnaphaseAnaphase

CentromeresCentromeres uncouple and spindle fibers spindle fibers shorten.

Sister chromatids Sister chromatids separate and move apart.

After separation, chromatidschromatids are now considered chromosomeschromosomes.

AnaphaseAnaphase

During this phase, the cell contains twice the normal number of chromosomeschromosomes.

Cell begins to elongateelongate.

At the end, there are equal numbers of chromosomeschromosomes at the poles.

AnaphaseAnaphase

No longer sister chromatidssister chromatids, now chromosomeschromosomes

centriolesspindle fibers

asterfibers

TelophaseTelophase

Cleavage furrowfurrow develops in animal cells (CytokinesisCytokinesis begins).

Cell plate Cell plate develops in plantsplants (no cleavage furrows in plants).

Nucleolus reappears.

cell plate

TelophaseTelophase

Nuclear membrane reappears.

ChromosomesChromosomes uncoil.

In the end, two genetically identical nuclei (karyokinesiskaryokinesis completed) are present.

TelophaseTelophase

cleavage furrow (cytokinesis)

nuclear membrane reforming nucleolus reappears

CytokinesisCytokinesis

Cytoplasmic divisionCytoplasmic division

Cell plate Cell plate complete in plantsplants

In the end, two separate daughter cells produced with single nucleus.

cell plate

Question:Question:

A cell containing 2020 chromosomeschromosomes at the beginning of mitosis would, at its completion, produce cells containing how many chromosomes eachchromosomes each?

Answer:Answer:

20 chromosomes20 chromosomes

Question:Question:

A cell containing 4040 chromatidschromatids at the beginning of mitosis would, at its completion, produce cells containing how many chromosomes eachchromosomes each?

Answer:Answer:

20 chromosomes20 chromosomes

What is cancer?

A cancer cell is a cell that grows out of control.

Unlike normal cells, cancer cells ignore signals to stop dividing, to specialize, or to die and be shed.

Growing in an uncontrollable manner and unable to recognize its own natural boundary, the cancer cells may spread to areas of the body where they do not belong.

White blood cells attack the cancerous cell!

Find your self:

How the cancerous cells look like?

How these cells affect the health?

How these cells spread? What causes the cancer in

human?

Website for you to visit:

http://www.cellsalive.com/mitosis.htm http://www.biology.arizona.edu/Cell_bio/tuto

rials/cell_cycle/cells 3.html http://www.accessexcellence.org/RC/VL/GG/

mitosis.php

http://training.seer.cancer.gov/module_cancer_disease/unit2_whatscancer3_cell_biology.html