CELL DIVISION NOTES

CELL DIVISION

The necessity for cell division

• Cell in the body are continuously
dividing, growing and dying

• Dead cell need to be replaced with new
cells

• Example : injury, hair grow, fingernail grow,
growth

6.1 CELL DIVISION

Mitotic cell division : the process that produce
new cells from one cell

Two stages in cell division involves

Karyokinesis Cytokinesis
(nuclear division) (cytoplasmic division)

HUMAN CELLS

GAMETES(REPRODUCTIVE CELLS)

SOMATIC CELLS

ORGANISM BODY CELLS

SOMATIC CELLS GAMETE
• All body cells • Reproductive cells

except gametes (sperms and ovum)
• Produced through • Produced through

mitosis meiosis
• Contain diploid • Contain haploid

number ( two sets of number ( one set of

chromosomes, 2n) chromosomes, n
• In human somatic • In human gametes,

cells, 2n = 46 n= 23

DIPLOID(2n) vs HAPLOID(n)

Homologous chromosomes:carry similar genetic information
1 pair homologous chromosomes:( 1 from mother, 1 from father)

Chromatin is a lower order of
DNA organization

Chromosomes are the higher order of
DNA organization.

All of those three structures are composed of
DNA and proteins within the nucleus, each is
uniquely defined.

CHROMOSOMES

Character of chromosomes in
different phase
All of those three structures are composed
of DNA and proteins within the nucleus,
each is uniquely defined.

Character of a man in different ages

CELL CYCLE

By cikgu nurhanis

6.2 CELL CYCLE & MITOSIS

What is cell

cycle?

• Sequences of events
involves DNA
multiplication & cell
division to produce
two daughter cells.

• Consist of :
Interphase (the longest
phase in cell cycle)
M phase

• Cell grow INTERPHASE • Continue grow
• Cell components as • Metabolically
S DNA SYNTHESISED
mitochondrion, DNA REPLICATE G2active
endoplasmic
reticulum produced • Dna synthesis occurs • Cell gather
at this stage • Dna in nucleus is energy
• Proteins used in cell
replicated • Make final
G1 cycle synthesised • Form two identical arrangement
• Nucleus looks big enter m phase
chromosomes named
RAPID GROWTH & sister chromatids PREPARATION
REPLICATION(COPYING) • Both chromatids NEXT STAGE
contain same copy of
ORGANELLES the dna molecules &
joined at centromere

M PHASE

MITOSIS CYTOKINESIS

Nuclear division Cytoplasmic
Consist of prophase, division
metaphase,
anaphase, telophase

MITOSIS

By cikgu nurhanis

WHAT IS MITOSIS?

• Nucleus division of parent into two nuclei
• Sam• e nSuammbeergecnhertoimc ocsoonmteenst as parents

Key notes:

Chromosomes:
•Chromatin shorten and thicken
•Sister chromatids form joined at centromere

Nucleus membrane:
•Start disintergrates

Centrioles: Moves opposite poles

Spindle fibre :Formed

Key notes:
Chromosomes:
•Become aligned in single row on equatorial
plane
Nucleus membrane:
•Start disintergrates
Centrioles:At the opposite poles
Spindle fibre: maintain the chromosomes at
the equatorial plane
Metaphase ends when centromere divided

Key notes:

Chromosomes:
•Centromere divides into two.
•Sister chromatids separated then attracted

to opposite poles.
•Spindle fibres: shorten, contract.
•Anaphase ends when chromatid arrives at

the pole.

Key notes:

Chromosomes:
•At poles, chromatids now known as

daughter chromosomes.
•Complete and identical chromosomes at

poles.
•Shaped as fine chromatin threads
•Nucleoli: formed again
•Spindle Fibres: disappear
•Nucleus membrane: formed
•Followed by cytokinesis

THE DIFFERENCES BETWEEN MITOSIS & CYTOKINESIS IN
ANIMAL CELLS AND PLANT CELLS

Cytokinesis is cytoplasm division immediately happens after nucleus formed
at the end of telophase

ANIMAL CELLS PLANT CELLS

Plasma membrane Vesicles formed combine to form cell plates
constrict in middle at centre cell
cell between two
Cell plates surrounded by new plasma
nuclei. membrane

Microfilament at New cell wall substance formed among spaces
point constriction cell plates.

will contract Cell plates expand outwards until combine
with plasma membranes
Cell will constrict until
split to form two Cellulose fibre produced by cell to strengthen new
daughter cells. cell walls

Two daughter cells formed has diploid
condition.



THE NECESSITY OF MITOSIS

6.3 MEIOSIS

By cikgu nurhanis

WHAT IS MIeosis?

• Cell division occurs in reproductive organs (testis,
ovary) to produce gametes (sperm and ovum)

• The gamete contain half number chromosomes
(haploid) of the parent cells (diploid)

Why meiosis is needed?

• Form gametes through gametogenesis
• Ensure diploid chromosomes number organism maintained.
• Produce genetic variation in the same species.
• Stages in meiosis
• Meiosis I consist of prophase I, metaphase I, anaphase I telophase I
• Meiosis II consist of prophase II, metaphase II, anaphase II telophase II

Meiosis I
Meiosis II

Meiosis I

Key Notes: Homologous chromosome pairing to form bivalent
Chromosomes:
Chromatin shorten , thicken and visble.
Homologous chromosomes pairing
(synapsis) to form bivalent (tetrad- four
chromatid for each homologous
chromosomes)
Crossing over- exchange genetic
material, produce new chromosomes
contain combination genes
Chiasma –point chromatids cross over
Nucleus membrane- disappear
Nucleoli- disappear
Centrioles-moves opposite poles
Spindle fibre- formed among centrioles

Key Notes:
Homologous chromosomes arranged
at equatorial plane.
Sister chromatids tied together,
centromere not separated.

Key Notes:
• Spindle fibres: contract

• Homologous chromosomes start to separate

pulled to opposite poles

• Each chromosomes ( pair of sister chromatids) tied
at centromere move as one unit.

Chromosomes arrive at opposite pole

Key notes:
Chromosomes : arrive at opposite pole
Polar cell contain haploid chromosomes
Spindle fibres : Disappear
Nucleoli: Reappear
Nuclear membrane : Formed
Cytokinesis occurs
End of Telophase I, two daughter cells
produced (haploid condition)

Interphase (meiosis I)- short and DNA not
replicate.

Key Notes:
Nucleoli disappear
Nuclear membrane disappear
Chromosomes: Sister chromatid
joined at centromere
Spindle fibres start to form

Nucleoli, nuclear membrane disappear

Key Notes: Chromosomes arranged along equatorial plane foe each daughter cell.

Chromosomes:

Arrange randomly on equatorial plane
In daughter cells

Chromatid tied to spindle fibres
at centromere

Centromere separates  Metaphase II ends

Key Notes:
Chromosomes:
Centromere on sister chromatids
starts to separate and led to opposite
poles.
Each chromatid at this stage known as
chromosomes.

Key Notes: 4 daughter cells contain haploid number of chromosomes
Chromosomes:

Arrived at poles

Number of chromosomes half from

parents

Spindle fibres : Disappear
Nuclear membrane: Reconstructed
Nucleoli : Reconstructed

Telophase II ends with:
Cytokinesis produced 4 daughter cells,
haploid (half from parent cell) and
Develop into gametes.

COMPARISON AND CONTRAST

BETWEEN MEIOSIS AND MITOSIS

SIMILARITIES
Both mitosis and meiosis undergoes stages Interphase and Prophase,

Metaphase , Anaphase and Telophase.
Both mitosis and meiosis pass the genetic information.

Mitosis Differences Meiosis

Growth, repair, replace Purpose process Gametes produced
worn out or dead cells

2 No. daughter cells 4

produced

46 (23 pairs) Number of 23 ( 23 unpaired
chromosome in chromosomes)
daughter cells
(human)

Diploid Ploidy Haploid

Yes Genetically identical NO
to parent

1 Division 2

6.4 ISSUES OF CELL DIVISION
ON HUMAN HEALTH

By cikgu nurhanis

Effect of Abnormal Mitosis
on Human Health

• Cell cycle controlled by each G1, S, G2
and M phase.

• Formation tumours caused by
uncontrolled cell division.

Types of Tumours

Benign tumour Malignant
tumour

Types of Tumours

Benign tumour Malignant
tumour

• Not dangerous • Called cancer
• Can be • Cells divide

removes continuously
• Develop to
surgically
tumour
• Cells will spread

and destroy

normal cell around

them
• Tissue’s function

around the cells

will affected
• Not identified early

stage
• Caused organ

damaged
• Causes death

CAUSES OF CANCER

• Caused by :
• Radiation ( x-ray, gamma rays,

UV rays)
• Chemical substance: tobacco

tar
• Carcinogens(formaldehyde-

colourless, strong smelling
gas,benzene)
• Genetic factors
• Bacteria
• Viruses

The Development of Breast Cancer

ABNORMALITY DURING DIVISION MEIOSIS

• Can cause genetic disease , Down syndrome (47chromosomes)
• Spindle failed to function during anaphase I or anaphase II
• Chromosome fails to separate (nondisjunction)
• Gamete will have abnormal number ( 22 or 24 chromosome)

FORMATION OF TRISOMY 21

• If fertilization between normal gamete(23 chromosomes) with abnormal
chromosomes

(24 chromosomes), zygote will carry 47 chromosomes (Down syndrome)
• Condition known as trisomy 21

This syndrome can

cause:
• Mental retardation
• Slanted eyes
• Slightly protruding

tongue