cell,its constituent and cell cycle

1. A TOUR OF THE CELL
1
Dr.Bhavna Tyagi(PG 1ST year)1

2. content
 History
 Defination of cell
 Types and difference between prokaryotic and
eukaryotic
 Cell theory
 Basic aspect
 Cell membrane
 Cytoplasm and its organelles
 Function of organelles
 Cytoskeleton
 Functional system of cell
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3.  Cell cycle
 Mitosis and Meiosis
 Checkpoints in cell cycle
 Apoptosis
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4. history
 Robert Hooke used simple lenses
to observe cork in which he saw
tiny compartments he called cells
(cellulae)
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5. What is a cell?
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6. An aggregate of cells in an organism that have
similar structure and function :Tissue
an organ (or viscus) is a collection of tissues
joined in a structural unit to serve a common function
An organism may be either unicellular (a single cell) or
comprise many trillions of cells
grouped into specialized tissues and organs.
cell 6
6

7. Types of cell
1.Prokaryotic cells :nucleus
without membrane eg .
Bacteria and Blue green algae
2.Eukaryotic cell : organised
nucleus and cell organelles eg .
Plants and animals
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8. Difference between prokaryotic and
eukaryotic
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9. CELL THEORY
 The Cell Theory
1. Schleiden (a botanist) and Schwann (a zoologist):
believed that all plants and animals consist of cells.
2. Virchow: cells come from preexisting cells.
The Cell Theory: three generalizations:
1. All organisms are composed of one or more cells.
2. The cell is the smallest unit having the properties of
life.
3. The continuity of life arises directly from the growth
and division of single cells.
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9

10. Basic aspects
 Structural Organization of Cell
 All cells have three basic parts:
• 1. Plasma membrane:- separates each
cell from the environment, permits the
flow of molecules across the
membrane
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10

11. • 2. A DNA-containing region occupies a
portion of the interior
• 3. The cytoplasm contains membrane-
bound compartments (except bacteria),
particles, and filament all bathed in a
semifluid substance
Continues…
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11

12. Cell membrane
 Biological membrane that separates
the interior of all cells from the outside
environment
 Selectively permeable to ions and organic
molecules and controls the movement of
substances in and out of cells.
 Protect the cell from its surroundings.
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12

13. Thin, pliable, elastic structure only
7.5 to 10 nm thick
Composed entirely of proteins
and lipids
Appears to be trilaminar in
electron microscope.
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14. Components of membrane
Lipid bilayer
Cholesterol
Carbohydrates
Proteins
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15. Fluid mosaic model of membrane
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16. CELL MEMBRANE consist of bilayer of
phospholipid molecules that are
amphipathic,i.e consist of polar head and
nonpolar tail
Polar head
(water loving)
Non polar tail
(water hating)
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17. PHOSPHO LIPID MOLECULE
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18. CHOLESTROL
MOLECULES
 CHOLESTROL MOLECULES are present in
the bilayer(1:1 ratio with the phosphate)
 Stabilize and regulate the fluidity of the
bilayer
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18

19. PROTEIN MOLECULES
2 types:
(a) Integral proteins:
Protrude all way through the membrane.
Provide structural channels(or pores)
through which water molecules and
water soluble substances(ions) can diffuse
between extracellular and intracellular fluid.
(b) Peripheral protiens: attached to only one
surface .
No penetration.
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19

20. FUNCTIONS OF TRANSMEMBRANE
PROTEIN
 CELL TO CELL adhesion
 CELL MATRIX adhesion
 Formation of pores or channels for
the transport of materials into and
out of the cell
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20

21. GLYCOCALYX
Membrane Carbohydrates
 Occur in combination with proteins
and lipids in form of glycoproteins or
glycolipids.
Entire outside surface of the cell often
has a loose carbohydrate coat called “
glycocalyx”
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22. 22
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23. Cytoplasm and its
organelles
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24. CYTOPLASM
 Material enclosed by plasma
membrane.
 Clear fluid portion of the cytoplasm
in which particles are dispersed is
called “cytosol”
 Occupies space between plasma
membrane and nuclear membrane
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24

25. Chemical composition of
protoplasm
 Water:75 -85%
 Protein :10-12%
 Lipid:2-3%
 Carbohydrates:1%
 Inorganic substances:1%
 DNA:0.4%
 RNA:0.7%
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25

26. Types of Organelles
 Nonmembranous organelles:
no membrane
direct contact with cytosol
 Membranous organelles:
covered with plasma membrane
isolated from cytosol
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26

27. Membranous Organelles
Endoplasmic reticulum (ER)
Golgi apparatus
Lysosomes
Peroxisomes
Mitochondria
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28. Non membranous organelles
 Ribosomes (free ribosomes and polysomes)
 Microtubules
 Centrioles
 Cilia and flagella
 Filaments
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28

29. THE NUCLEUS
 Discovered by
Robert Hooke in
1831
 Is the cell’s control
center
 Contains DNA:
genetic material
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29

30. The Nucleus contains DNA,protein called as
NUCLEOPROTEIN and some RIBONUCLEIC ACID.
2 TYPES OF NUCLEOPROTEIN
HISTONE NON HISTONE
Control the coiling and expression of the genes
encoded by DNA strands n NON PROTEIN
HISTONES
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30

31.  NUCLEI are hetrogenous
structures with
electron-dense(dark)
and electron-
lucent(light)
 HETROCHROMATIN H,
consist tightly coiled
inactive chromatin found
irregular clumps
 EUCHROMATIN E,
represents that part of
the DNA that is active in
RNA synthesis
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31

32.  CHROMATIN –collectively ,
HETROCHROMATIN and EUCHROMATIN
are known as CHROMATIN
 CHROMATIN is a highly organised but
dynamic structure with the individual
chromosome tending to clump in
particular areas of the nucleus ,known
as chromosome territories
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32

33. THE NUCLEOLUS
 It is an accumulation of large amount of
RNA and proteins.
 Nucleolus becomes considerably enlarged
when the cell is actively synthesizing
proteins.
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34. MICROGRAPH OF NUCLEOLUS
 F- filamentous component
 G-granular component
 The filamentous component
are the site for the ribosomal
RNA synthesis
 RIBOSOME assembly take
place in the granular
component
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34

35. NUCLEAR
ENVELOPE The Nuclear envelop
NE,which encloses the
nucleus N,Consist of 2
layers 0f membrane with
the
INTERMEMBRANOUS
or PERINUCLEAR
SPACE between
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35

36. NUCLEAR PORES
 The nuclear envelop contain
numerous NUCLEAR PORES (NP) at
the margins of which the inner and
outer membranes become
continuous
 NUCLEAR PORES permit and
regulate the exchange of
metabolities ,macromolecules and
ribosomal subunits between the
nucleus and cytoplasm
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36

37. Endoplasmic Reticulum
 This is a complex network or reticulum of
membranes running throughout the cytoplasm
 Walls are constructed of lipid bilayer membranes
that contain large amounts of proteins
 Contain of flattened membrane bound sacs called
CISTERNAE
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37

38. Endoplasmic Reticulum
CONT.
 Cisternae are storage chambers within
membranes
2 types:
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
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38

39. ROUGH ENDOPLASMIC
RETICULUM
It has ribosomes
attached throughout the
surface
This type of ER is
present in the cell which
shows active protein
synthesis
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39

40.  Micrograph shows
rER tends to b
profuse and to
form closely
packed laminae of
flattened
cisternae
 NOTE the close
association
between the rER
and the outer lipid
bilayer of the
nuclear envelop
NE with which its
in continuity
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40

41. Smooth Endoplasmic
Reticulum
No
ribosomes
attached
Tubular
Membrane
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41

42. Function of sER and eER
Active
transport
Forms
skeletal
frame work
Metabolic
activities due
to enzymes
Provide
increase
surface area
Formation of
new nuclear
membrane
during cell
division
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42

43. Function of sER
GLYCOGEN SYNTHESIS
LIPID AND STEROID
SYNTHESIS
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43

44. FUNCTION OF rER
Site for protein synthesis
Help in transport of protein
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45. GOLGI APPARATUS
 Golgi apparatus is made up of one or
more golgi bodies which are stacks
of 3 – 10 flattened sacs and vesicles
 Closely related to endoplasmic
reticulum
 Prominent in secretory cells.
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45

46. GOLGI
APPARATUS
Vesicles from the endoplasmic reticulum
(via the vesicular-tubular clusters) fuse with the network and
subsequently progress through the stack
to the trans Golgi network, where they are packaged and
sent to their destination. Each region contains different
enzymes which selectively modify the contents
depending on where they reside.
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46

47. FUNCTIONS
 Formation of cell wall
 Synthesis of glycolipid
 Lysosomes formation
 Water balance
 Lipid secretion
 Protein secretion
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48. Lysosome
membrane-bound cell organelle
They are structurally and chemically spherical
vesicles containing hydrolitic enzymes
250 to 750 nm in diameter.
Surrounded by a typical lipid bilayer
membrane.
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48

49. Enzymes of the lysosomes are synthesised in
the rough endoplasmic reticulum.
The enzymes are released from Golgi
apparatus in small vesicles which ultimately
fuse with acidic vesicles called endosomes,
thus becoming full lysosomes
They are popularly referred to as "suicide
bags" or "suicide sacs"
of the cell
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49

50. Types of lysosomes
 Primary –these are small vesical like structure
produced from the golgi apparatus
 Secondary-they are formed when phagosomes
fuse with already existing primary lysosomes
 Residual bodies
 Autophagic vacuoles –these lysosomes
envelope and attack intracellular organelles
like mitrochondria etc and digest them
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51. FUNCTIONS
Provide an intracellular digestive system that
allows the cell to digest within itself
(a) damaged cellular structures
(b) food particles that have been
ingested .
(c) unwanted matter such as bacteria.
Autolysis of a cell by release of the enzymes
with in the cell
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51

52. Peroxisomes
 Are enzyme-containing vesicles
 Break down fatty acids
 Membrane sacs containing oxidases and
catalases to neutralize free radicals that are
formed during catabolism of organic molecules
 Produce hydrogen peroxide (H2O2)
 Peroxisomes not made by Golgi apparatus rather
formed by self-replication.
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52

53. Peroxisomes
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54. MITOCHONDRIA
Power house of the cell.
Present in all areas of the cell’s
cytoplasm.
Variable in size n shape
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54

55.  Two lipid bilayer protein
membrane: outer and
inner membrane.
 Many infoldings of inner
layer forms shelves onto
which oxidative enzymes
are attached.
 Inner cavity of
mitochondria is filled with
matrix that contains large
quantity of dissolved
enzymes that are
necessary for extracting
energy from nutrients.
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55

56. The cytoskeleton
Cytoskeleton: Supporting
framework
Three main types : microfilament,
microtubules and intermediate
filament
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56

57. FILAMENTS AND TUBULAR
STRUCTURES
 Microfilaments
Thin filaments (<6nm diameter)
 Composed of the protein actin
 Usually at periphery of the cell
Functions:
provide additional strength by attaching the membrane
to the cytoplasm
Attach integral proteins to cytoskeleton
Pairs with thick filaments of myosin for muscle
movement
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57

58. Intermediate Filaments & Thick Filaments
Intermediate Filaments:
7-11 nm diameter
Mid-sized between microfilaments and thick
filaments
Durable, type varies with cell
Functions:
• strengthen cell and maintain shape
• stabilize position of organelles
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58

59. Thick Filaments
15 nm diameter
Composed of myosin
Muscle cells only
Function
Interact with actin to produce
movement
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60. Microtubules
 Large (25nm diameter), hollow tubes
 Composed of tubulin protein
 Originate from centrosome
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61. Functions
 Foundation of the cytoskeleton
 Allows the cell to change shape and assists in
mobility
 Involved in transport
 Makes up the spindle apparatus for nuclear division
(mitosis)
 The structural part of some organelles
Centrioles, cilia, flagella
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61

62. Centrioles in the Centrosome
Centrioles : form spindle apparatus during cell
division
Centrosome: cytoplasm surrounding centriole near
the nucleus
 Consists of matrix and paired centrioles
 Responsible for assembling spindle apparatus
during mitosis
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62

63. Cilia and Flagella
 Hair like projections
 Contain a microtubule core with cytoplasm
covered in plasma membrane
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63
63

64. Cilia: Short, numerous
Function: sweep substances
over cell surface
Flagella: Long, singular
Function: propel cell through
environment
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64

65. FUNCTIONAL SYSTEMS OF THE
CELL Ingestion by the cell –
ENDOCYTOSIS The plasma membrane envelops small
particles or fluid, then seals on itself to form
a vesicle or vacuole which enters the cell:
 Phagocytosis
 Pinocytosis
 Receptor-Mediated Endocytosis
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66. Phagocytosis (cell eating)
 In phagocytosis, a cell engulfs a particle by
Wrapping pseudopodia around it and packaging it
within a membrane enclosed sac large enough to
be classified as a vacuole called as phagosomes
 The particle is digested after the vacuole fuses
with a lysosome containing hydrolytic enzymes.
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67. phagocytosis 67
67

68. Pinocytosis (cell drinking)
Endosomes “drink” extracellular fluid
and enclose it in membranous vesicles
at the cell surface
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69.  Mitosis and Meiosis
 Cell cycle
 Checkpoints in cell cycle
 Apoptosis
 These topic will be cover in next seminar
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69

70. Bibliography :
 wheater’s functional histology . A text
and colour Atalas . fifth edition
 Arthur C. Guyton; John E. Hall. Text
book of Medical Physiology. Tenth
edition.
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70

71. THANK YOU
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71

72. Cell cycle and
replication
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73. cell cycle
Proliferating cell progress
through a series of checkpoints
and defined phases called THE
CELL CYCLE
CELL CYCLE consists of
G1,S,G2,M,G0 phases
73

74. CELL CYCLE
cell growth, organelle
duplication, protein
synthesis, synthesizes
enough cytoplasm for
2 cells
DNA replication and
histone synthesis.8-12
hours after mitosis
and 7-8 hrs for
completion.
finishes protein
synthesis and centriole
replication
Mitosis involves division of
the chromosomes.
Cytokinesis involves
division of the cytoplasm.
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75. Cell division
 Multiplication of cells takes place by division of pre-existing cells.
Body (somatic) cells divide in 3 stages:
DNA replication duplicates genetic material
exactly
Mitosis divides genetic material equally
Cytokinesis divides cytoplasm and organelles
into 2 daughter cells
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76. Mitosis
What is the purpose of mitosis?
Cell division
 Products genetically identical
 Growth of organism
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77. Stages
 The period during which the cell is actively
dividing is the phase of mitosis
 The period between two successive
divisions is called the interphase
 Interphase is often included in
discussions of mitosis, but interphase is
technically not part of mitosis, but rather
encompasses stages G1, S, and G2 of the
cell cycle.
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78. Divided into
Prophase
Metaphase
Anaphase
Telophase
78

79. Interphase The cell is engaged in metabolic
activity and performing its prepare
for mitosis (the next four phases that
lead up to and include nuclear
division).
Chromosomes are not clearly
discerned in the nucleus, although a
dark spot called the nucleolus may
be visible.
The cell may contain a pair of
centrioles (or microtubule
organizing centers in plants) both of
which are organizational sites for
microtubules.
79

80. prophase  Chromatin in the nucleus begins to
condense and becomes visible in
the light microscope as
chromosomes.
 The nucleolus disappears.
 Centrioles begin moving to
opposite ends of the cell and fibers
extend from the centromeres.
 Some fibers cross the cell to form
the mitotic spindle.
80

81. Prometaphase The nuclear membrane
dissolves, marking the
beginning of
prometaphase.
Proteins attach to the
centromeres creating the
kinetochores.
Microtubules attach at the
kinetochores and the
chromosomes begin
moving. 81

82. Metaphase
 Spindle fibers line the chromosomes
along the middle of the cell
nucleus. This line is referred to as
the metaphase plate.
 Polar microtubules extend from the
pole to the equator, and typically
overlap
 Kinetochore microtubules extend
from the pole to the kinetochores
 This organization helps to ensure
that in the next phase, when the
chromosomes are separated, each
new nucleus will receive one copy of
each chromosome 82

83. Anaphase  The paired chromosomes
separate at the
kinetochores and move to
opposite sides of the cell.
 The chromosomes are
pulled by the kinetochore
microtubules to the poles
and form a "V" shape
 Motion results from a
combination of
kinetochore movement
along the spindle
microtubules and through
the physical interaction of
polar microtubules.
83

84. Telophase  Chromatids arrive at
opposite poles of cell,
and new membranes
form around the
daughter nuclei.
 The chromosomes
disperse and are no
longer visible under the
light microscope.
 The spindle fibers
disperse, and
cytokinesis will start
84

85. Cytokinesis  In animal cells,
cytokinesis results
when a fiber ring
composed of a
protein called actin
around the center of
the cell contracts
pinching the cell into
two daughter cells,
each with one
nucleus.
 In plant cells,
synthesis of new cell
wall between two
daughter cells rather
than cleavage furrow
in cytoplasm
85

86. Meiosis
 Function
Reduction division (23 chromosomes per gamete)
 Mechanism
Each homologue (e.g. “chromosome 7”) replicates to give
two sister chromatids
Homologues pair (e.g. maternal chromosome 7 and paternal
chromosome 7)
Exchange of material between non-sister chromatids:
crossing-over, recombination
Chiasmata (visible cytologically) are the physical
manifestations of crossing-over
86

87. Meiosis
Introduction
 Meiosis consist s of two successive
divisions called the first and the second
meiotic divisions
 1st meiotic division
Prophase is prolonged
Divided into 4 stages
87

88. Meiosis I
Fig A represents leptotene stage-
chromosomes become visible
consist 2 chromatids ,cnt distinguish
Fig B represents zygotene stage-
pairing of chromosome called synapsis
The two chromosomes together c/a
bivalent
Fig C represents pachytene stage -4
chromatid visible c/a tetrads,2 central
and 2 peripheral chromatids.
Cont.. 88

89. Fig D cont. pachytene stage-2
central chromatid cross over c/a
crossing over
The point of crossing c/a chiasmata
Fig E represents Diplotene stage-2
chromosomes of a bivalent try to
move apart
Exchange of genetic material occur
89

90. Nuclear membrane disappear
Spindle has formed
Chromosomes attach to the spindle at equator
Chromosome attach by centromere 90

91. One entire chromosome of the pair moves to
either pole
NOTE that the centromere does not divide
91

92. Similar to mitosis
NOTE that the chromosome in each cell have been reduced
to half the diploid number 92

93. 2nd mitotic division
The 1st mitotic division is
follow by the short
interphase
There is no duplication of
DNA
2nd meiotic division
similar to the mitosis
93

94. Regulation of cell cycle
94

95. Nuclear transcription factor
Quiescent cell receive a signal to divide
MYC protein binds to DNA
Transcriptional activation of several growth
related genes including cyclin dependent
kinases
Drive cell into cell cycle MYC decline
95

96. Cyclins and Cyclins –
Dependent Kinases
Phosphoryl
ation of
RB,
molecular
on off
switch
G2/M transition initiated by
E2F mediated transcription
of cycline A,which form
complex cycA cdk2 tht
regulates mitotic prophase
Main mediator tht propel the
cell beyond prophase is cyc B-
cdk1 complex .activation of
complex leds to breakdown of
nuclear envelop n initiates
mitosis 96

97. Cell cycle inhibitor
97

98. cell cycle check points
 Cell cycle has its own internal control called as
checkpoints
 2 main check points ,1 at G1/M transition and another at
G2/M
 S phase is point of no return ,before cell makes the final
commitment to replicate ,G1/S checkpoint checks for DNA
damage
 DNA damage after its replication can still be repaired as
long as the chromatids have not separated .the G2/M
checkpoint monitor the completion of DNA replication and
checks whether the cell can safely initiates mitosis and
separates sister chromatids
98

99.  G1/S checkpoint , cell cycle arrest is
mostly mediated through p53,which
induce cell cycle inhibitor p21
 Arrest of cell cycle by G2/M checkpoints
involve the both p53 dependent via
cyclin A/cdk-2 and independent via cdc
25 mechanism
99

100. p53
 Also called as “guardian of the genome”
 Present on chromosome 17
 Most mutated gene in human cancer p53 links cell
damage with DNA repair ,cell cycle arrest and
apoptosis.
 P53 links cell damage with DNA repair ,cell cycle arrest
and apoptosis
 In reponse to DNA damage,it is phosphorylated by
gene that sense the damage and are involved in DNA
repair
 P53 assist in DNA repair by causing G1 arrest and
inducing DNA repair
 A cell with DNA damaged tht cant be repaired is
directed by p53 to undergo apoptosis
100

101. 101
Regulation of
cell cycle

102. APOPTOSIS
PROGRAMMED CELL DEATH
 It is a pathway of cell death that is
introduced by a tightly regulated suicide
program in which cells destined to die
activate enzymes that degrade the cell’s
own nuclear DNA and nuclear and
cytoplasmic proteins.
102

103. (a) In phisiologic conditions:
Normal phenomenon that serves to eliminate cells that
are no longer needed and to maintain a steady number of
various cell populations in tissues.
examples:
 During embryogenesis.
 Involution of hormone-dependent tissues upon hormone
withdrawal.
 Cell loss in proliferating cell populations , such as
immature lymphocytes in the bone marrow and thymus .
103
causes

104.  In pathological conditions:
 Eliminates cells that are injured beyond repair
without eliciting a host reaction, thus limiting
collateral tissue damage.
 DNA damage: radiation anticancer drugs and
hypoxia.
 Accumulation of mis folded proteins- because
of mutations in the genes encoding these
proteins or damage caused by free radicals.
 Viral infections like HIV
104

105. MECHANISM
105

106. Regulation
106

107. Bibliography :
 (1)Robbins and Cotran : Pathologic basis of disease:
seventh edition
 (2)Gobind Rai Garg Sparsh Gupta :Review of pathology
and genetics :fifth edition
 (3) Inderbir singh :Human Embryology : seventh edition
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