normal cell cycle, mitosis and meiosis

1. CELL
DIVISION
PRESENTED BY,
Dr ASMIN P K
1ST YEAR POST GRADUATE

2. CONTENTS
■ INTRODUCTION
■ BASIC CELL STRUCTURE
■ CELL CYCLE AND CELL DIVISION
■ MITOSIS
■ MEIOSIS
■ CONCLUSION
■ REFERENCES

3. INTRODUCTION
HISTORY:
■ In 1665,robert hook used microscope to examine
a dead plant cell.
■ He named it cell because it looked like small
Rooms that monks lived – CELLS.
■ IN 1673, LEEUWENHOOK (a Dutch microscope maker)
was 1st to observe living organism.

4. PROKARYOTES:THE 1ST CELLS
 Cells that lack nucleus or membrane
bound organelles.
 Simplest type of cells.
 Single, circular chromosomes.
 Nucleoid region contains DNA.
 Surrounded by cell membrane and
PEPTIDOGLYCAN cell wall.
 Contain RIBOSOMES (no membrane) in
their cytoplasm to make proteins.

5. EUKARYOTES:
 Have a nucleus and membrane bound
organelles.
 More complex type of cells.
 Includes protists, fungi , plants
and animals.
 Contain 3 basic cell structures:
1:CELL MEMBRANE
2:CYTOPLASM WITH ORGANELLES
3:NUCLEUS

6.  BASIC CELL
STRUCTURE:
CELL MEMBRANE:
Bilipid layer of phospholipids and proteins.
Surrounds outside of all cells.
It controls what enters or leave the cell.
PHOSPHOLIPIDS:
HEADS: hydrophilic(contain glycerol and
phosphates).
TAILS: hydrophobic (made up of fatty
acids)

7. CYTOPLASM:
Jelly like
substances
enclosed by cell
membrane.
Provides a
medium for
chemical reactions
to take place.
Contains organells
to carry out
specific jobs.
ORGANELLES: Are microscopic.
Perform various
functions of cells.
Found in
cytoplasm.
May or may not be
membrane bound.

8. NUCLEUS:
■ Largest organelle.
■ Bounded by nuclear envelope with pore.
■ Contains DNA in chromosomes.
■ Controls the normal cell activities.
■ Each cell has fixed number of CHROMOSOMES that carry genes.
■ Genes control cell characteristics.

9. NUCLEAR ENVELOPE:
Nuclear contents are set apart from cytoplasm by a double membrane- NUCLEAR ENVELOPE
Narrow inter membrane space (40-70 micrometre) – PERINUCLEAR CISTERNA.
Contain nuclear pore for materials to
Enter and leave nucleus.
Inside nucleus genetic material is found.
In non-dividing cells –DNA spread out as CHROMATIN.
In dividing cells – DNA is condensed and wrapped around proteins forming CHROMOSOMES.

11. CELL CYCLE AND CELL DIVISION

12. WHY DO CELL DIVIDE?
1. Reproduction
2. Growth and Development
3. Tissue Renewal

14. ■ All cells are derived from pre-existing cells.
■ New cells are produced for growth and to replace damaged or old cells.
■ Differs in prokaryotes (bacteria) and eukaryotes ( protists , fungi , plants and
animals).
■ Cell division consist of 4 steps:
1. A SIGNAL TO DIVIDE
2. DNA REPLICATION
3. DNA SEGREGATION
4. CYTOKINESIS – DIVIDING THE CYTOPLASM

15. CELL DIVISION IN PROKARYOTES:
■ Prokaryotes such as bacteria divide into two identical cells by the process of
BINARY FISSION.
■ Binary fission
– 3 main steps:
1: DNA Replication—DNA is copied, resulting in 2
identical chromosomes
2: Chromosome Segregation—2 chromosomes
separate, move towards ends (poles) of cell.
3: Cytokinesis—cytoplasm divides, forming 2 cells
– Each new daughter cell is
genetically identical to parent cell

16. EUKARYOTIC
CELL CYCLE

17.  5 PHASES OF CELL CYCLE.
1. G1 – PRIMARY GROWTH PHASE.
2. S – SYNTHESIS , DNA REPLICATED.
3. G2 -SECONDARY GROWTH PHASE.
4. M – MITOSIS
5. C - CYTOKINESIS
INTERPHASE (LONGEST
PHASE)
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE

18. INTERPHASE:

19. INTERPHASE:
■ period of growth and DNA replication between cell divisions
■ THREE PHASES:
1. G1 Phase
■ cell increases in size.
■ Cells just finished dividing so in GAP1 the cell is recovering from mitosis.
2. S Phase
■ Replication of chromosomes
■ Now two strands called sister chromatids joined by a centromere.
3. G2 Phase
■ This is the preparation for mitosis.
■ organelles double
■ new cytoplasm forms
■ All other structures needed for mitosis form
MITOSIS BEGINS
AFTER G2 AND ENDS
BEFORE G1

20. CELL DIVISION IN
EUKARYOTES –
MITOSIS:
■ mitosis- mechanism by which
somatic eukaryotic cells produce
identical daughter cells.
■ involves partition of both
cytoplasmic and nuclear structure.
■ strictly applied , mitosis is used to
describe the duplication and
distribution of chromosomes , the
structure that carry genetic
information.

21. PROPHASE
■ CELLS BEGINS THE PROCESS OF DIVISION.
■ CHROMOSOMES CONDENSES.
■ NUCLEOLUS, A ROUNDED STRUCTURE SHRINKS
AND DISSAPPEARS.
■ CENTRIOLES MIGRATE TO OPPOSITE POLES OF
THE CELL.
■ ASTERS AND SPINDLE FIBRES ARE FORMED.

22. METAPHASE
■ Chromosomes line up at the equator of cell
(metaphase plate) with centrioles at opposite
ends and spindle fibres attached to centomere

23. ANAPHASE
■ Centromeres divides.
■ Each chromosomes separates into two identical
chromosomes.
■ Pulled to opposite ends of cells by spindle fibres.

24. TELOPHASE
 The nucleus divides.
 Chromosomes are at the poles of
cells.
 Nuclear envelope reforms
around the two sets of
chromosomes.
CYTOKINESIS:
 Division of cytoplasm.
 In animal cell a cleavage furrow
forms and seperates daughter
cells.

25. CYTOKINESIS

26. CONTROL
OF THE
CELL
CYCLE
Regulatory
proteins called
cyclins control
the cell cycle
at checkpoints:
G1
Checkpoint—
decides
whether or not
cell will divide.
S
Checkpoint—
determines if
DNA has been
properly
replicated.
Mitotic Spindle
Checkpoint—
ensures
chromosomes
are aligned at
mitotic plate.

28. UNCONTROLLED
MITOSIS??
■ If mitosis is not controlled, unlimited cell division occurs
causing cancerous tumours.
■ ONCOGENES Are special proteins that increase the
chance that a normal cells develop into a tumour cell.
■ BENIGN TUMOURS: Abnormal cells that remain at the
original site and be removed by surgery.
■ MALIGNANT TUMOURS: Becomes invasive and
spreads to neighbouring tissue and cells (cancer).

30. MEIOSIS

31. MEIOSIS:
■ Preceeded by interphase which includes chromosome replication.
■ Called as reduction division.
■ Original cell is diploid (2n).
■ 4 daughter cells produced that are monoploid (1n).
■ Daughter cells contain half the number of chromosomes as the original cells.
■ Produces gametes ( eggs and sperms).
■ Occurs in testes in males (spermatogenesis).
■ Occur in ovaries in females (oogenesis)

32. IMPORTANCE OF MEIOSIS..
■ It is fundamental basis of sexual reproduction.
■ Why cant mitosis be cell division process that runs sexual reproduction??
■ What would happen to the chromosome number from one generation to next??
46
92
184
368
736
1472

33. REPRODUCTION IN HUMANS
■ Fusion of 2 gametes to produce a single zygote.
■ Introduces a greater genetic recombination's.
■ With exception of self-fertilizing organisms, zygote has gametes from two
different parents.
■ At fertilization, 23 chromosomes are donated by each parent (total 46 or 23
pairs).
■ Gametes (sperm/ova) – contain 22 autosomes +1 sex chromosomes
■ Are haploid (n=23 in humans)

34. ■ Fertilization results in
diploid zygote.
■ Diploid cell – 2n=46 (n=23
in humans).

35. VARIATION
■ Also known as GENETIC
RECOMBINATION
■ Important to population as
the raw material for
NATURAL SELECTION.
■ All organisms are NOT
alike
■ Strongest “most fit” survive
to reproduce & pass on
traits

36. TERMINOLOGI
ES
Chromatin - thin
fibrous form of
DNA and proteins
Sister
chromatids-
identical structures
that result from
chromosome
replication, formed
during S phase
Diploid - two sets
of chromosomes
(2n), in humans 23
pairs or 46 total
Haploid - one set
of chromosomes
(n) - gametes or
sex cells, in
humans 23
chromosomes

37. ANATOMY OF A CHROMOSOME:
■ Centromere - point where sister chromatid
are joined together.
■ P=short arm; upward
■ Q=long arm; downward
■ Telomere-tips of chromosome

38. KARYOTYPI
NG
■ An organized picture of the
chromosomes of a human arranged
in pairs by size from largest to
smallest.
■ Pairs 1-22 called AUTOSOMES.
■ Last pair are SEX
CHROMOSOMES.
■ Shows the chromosomes as
they appear in metaphase.

39. NORMAL
KARYOTYPE
■ WHY?
■ IS IT A MALE OR A
FEMALE?

40. MEIOSIS:
■ Meiosis involves 2 divisions:
1: MEIOSIS 1
2: MEIOSIS 2
 MEIOSIS 1:
a. PROPHASE 1:
 Synapsis occurs.
 Homologous chromosomes pair up.
 Each group is made up of 4 chromatids.
 Each group of 4 chromatids = TETRAD.
 CROSSING OVER – When parts of non sister chromatids
change places. (increase genetic variations).

43. b. Metaphase 1:
 Tetrads are aligned at equator.

44. C. Anaphase 1:
 Tetrads split and chromosomes
( in replicated form ) move to opposite pole.

45. D: Telophase 1:
 Two cells forms – each cell is haploid but
each chromosome is in replicated form.

46. ■ INTERPHASE / INTERKINESIS:
 DNA is in chromatin form.
 No DNA replication occurs - WHY?
 Because each cell contains chromosomes
already in replicated form –no need to copy.

48.  MEIOSIS 2
■ Same as mitosis.
a. Prophase 2:
 Each cell is haploid with chromosomes
in replicated form.

49. b: Metaphase 2:
 Chromosomes align at the equator
in both cells.

50. C: Anaphase 2:
 Chromosomes separates .
 Chromatids move towards opposite poles.
 Centromere splits.

51. D: Telophase 2 and Cytokinesis:

52. NON-DISJUNCTION
■ Meiosis is prone to error. In some cases,
chromosomes fail to split properly in either
Anaphase I or Anaphase II.
■ Non-disjunction results with the production of
zygotes with abnormal chromosome numbers
(abnormal amount of DNA) is damaging to the
offspring.
■ Incidences of Non-Disjunction are strongly
correlated with maternal age…

53. ■ Non-disjunctions usually occur in one of two fashions.
■ The first is called Monosomy
■ the second is called Trisomy.
■ If an organism has Trisomy 18 it has three chromosomes in the 18th set.
■ Trisomy 21…. Three chromosomes in the 21st set.
■ If an organism has Monosomy 23 it has only one chromosome in the 23rd set

54. COMMON
NON-
DISJUNCTI
ON
DISORDERS
Down’s
Syndrome
– Trisomy
21
Turner’s
Syndrome
–
Monosomy
23 (X)
Klinefelter's
Syndrome
– Trisomy
23 (XXY)
Edward’s
Syndrome
– Trisomy
18

55. DOWN
SYNDROME
■ Trisomy 21
■ Due to nondisjunction
(chromosome did not
separate evenly)
■ Folds over eyes
■ Sluggish muscles
■ Mental Problems
■ (IQ often below 50)- but
■ Some much higher

56. ■ The most common
chromosome number
abnormality
■ Small head, ears, mouth
■ round face, short neck and arms
■ flattened nose bridge
■ small, irregular teeth
■ Short Stature
■ heart defects
■ susceptibility to
respiratory infection ,
leukemia, Alzheimer’s.

57. Does the
mother’s age
matter?
■ As the age of the mother
increases above 30, the
frequency of Trisomy 21
also increases

58. TURNER SYNDROME
■ XO (only one X)
■ Short
■ often web of skin between neck and shoulders
■ sterile
■ poor breast development

59. KLIENFELTERS
SYNDROME
■ 47 XXY syndrome
■ male
■ feminine body contours (wider hips)
■ 1 in 500 to 1,000 newborn males

60. WHAT ABOUT
MUTATIONS?
■ most often brought on by problems that occur
during meiosis or by mutagens (chemicals,
radiation, etc.) = cancer-causing agent
■ Often harmful

61. CAN YOU
FIND THE
CHANGE
S?

62. DELETION
■ Fragment of the chromosome is lost.
■ Could even be fatal

63. DUPLICATION
■ Fragment of one chromosome attaches to a
homologous chromosome
■ Maybe no harm.

64. TRANSLOCATION
■ Fragment reattaches in reverse direction (less
likely to produce harm
■ If all parts are transferred evenly, then no harm.
■ If also duplication or deletion, then changes in
genetic make-up.

65. INVERSION
■ The chromosome breaks in
two places, a piece of the
chromosome is removed
and the chromosome
pieces remaining rejoin.
■ Inversions, by definition, do
not involve loss or gain of
chromosomal material.

66. CONCLUSION:

67. REFERENC
ES:
■ Cooper M G , Hausman E.R ,(2007) . The
cell –a molecular approach .Ch.: 16.5-16.9
4th ed . Washington D C : ASM Press and
Sunderland , p: 670-682
.
■ Paulse F D ,(1996) .The nucleus and cell
cycle . Basic histology . 3rd ed . Stamford,
CT: Appleton and Lange , p:35-44.
.
■ Robert sneden (2007).cells and life. Cell
division and genetics . 2nd ed. Heinemann
– raintree
■ Sadler T W ,(2000) . Langmans Medical
Embryology- 8th ed . Philadelphia PA :
Lippincott Williams & Wilkins