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Lecture Delivered at KMC – IC
3 October 2011
Format of Lecture
 Introduction on Cell Cycle
 Concept of Cell Division
 Types of Cell Division
 Role of Chromosomes in Cell Division
 Mitosis: Technical Characteristics
 Meiosis: Technical Characteristics
 Overall Learning Outcome
Introduction on Cell Cycle
 Distinction between Living and Non-Living matters
 Living things reproduce and they have a capacity to
procreate
 Procreation in the living organism has a cellular basis
 A great German Physician – Rudolf Virchow put this
distinction very brilliantly – Where a cell exists, there
must have been a preexisting Cell, just as the animal
arises only from an animal and the plant only from a
plant
Continued:
 Rudolf Virchow (1821 – 1902) explained this concept of
cell cycle by using a Latin axiom “Omnis cellula e
cellula” – meaning every cell from a cell.
 The continuity of life is based on the reproduction of
cells – cell division
 Virchow extended his argument on the basis of the
existing cell theory proposed by Schleiden and
Schwann
Rudolf Virchow (1821-1902)
Postulates of Cell Cycle
 All living organisms are composed of cells and cell
products
 There are considerable similarities in the chemical
constitution and metabolic activities of all cells
 The total activities of an organism is the sum of the
activities and interactions of its independent cell units
The Cell Cycle
Structural Types of Cell
 Prokaryotic Cell
 Eukaryotic Cell
----- Prokaryotic Cell – Greek word combination of the
word Pro means first and Karyon means nucleus. The
Prokaryotic cells are in the form of bacteria and blue
green algae. These are very small and show primitively
organised nucleus and cytoplasm
----- Eukaryotic Cell – Greek word combination of the
word Eu means true and Karyon means nucleus. The
Eukaryotic cells are found in the most of the algae,
fungi, plants and animals.
Difference Between Prokaryotic
and Eukaryotic Cells
 Prokaryotic Cell
a) Nuclear membrane
b)
c)
d)
e)
absent
Nucleolus absent
Lack of clearly defined
membranes
Mitotic apparatus
absent
Nucleus diffused or
incipient
 Eukaryotic Cell
a) Nuclear membrane is
b)
c)
d)
e)
present
Nucleolus is also
present
Chromosomes are
made up of DNA
Mitotic apparatus
present
Nucleus is well
organised
Biological Organisation of
Protoplasm
 Protoplasm is bounded by a cell membrane. It is
further divisible into cytoplasm and nucleoplasm
 Nucleoplasm is enclosed by the nuclear membrane
 The protoplasm is highly organised and it consists of a
number of organelles which are highly ordered
structures performing various functions
 The Protoplasm also contains a number of depositions
called deutoplasmic substances and vacuoles
Concept and Key Roles of Cell
Division
 Cell Division plays several important roles in the life of
an organism
To explain this – one can take an example of amoeba –
because it is a unicellular organism and when it divides
and forms duplicate offsprings - the division of one
cell reproduces an entire organism
Cell division is a dynamic process by which cells multiply
in number leading to the production of new cells.
Continued:
 Without Cell division, multicellular organisms cannot
grow
 When cell divides, each cell is a complete cell in itself.
 Immediately following division, the daughter cells may
be smaller than the parent cell but they grow rapidly
and soon reach the size of the original cell.
 In real sense, cell division is a process of duplication or
multiplication rather than the division in the usual
sense.
Continued:
 Cell division continues to function in renewal and
repair
 It replaces cells that die from normal wear and tear or
accidents.
 Cell division process is an integral part of the cell cycle
 How cell division distributes identical genetic material
to daughter cells
 Understanding of the cellular mechanics of cell
division is very essential for a scholar
Continued:
 Knowledge on the molecular control systems that
regulates progress through the cell cycle will also be
necessary
 What happens when the control system malfunctions
will also be useful to understand.
 Relevance of Cell Cycle regulation – an active area of
research across the globe.
Role of Chromosomes in Cell
Division
 A chromosome is a body having special organisation,
individuality and functional qualities
 It is capable of reproducing itself through successive
cell divisions
 There are two basic types of chromosomes found in
living organisms - a) those found in Prokaryotes –
single circular DNA not associated with basic protein
(histone); b) true chromosomes characteristics of
eukaryotes, this contains DNA, RNA associated with
histones and other proteins
Chromosomes
 The chromosomes exhibit great variations in their
shape, number and length.
 The shape of the chromosomes depends on the
location of the centromere – the centromere is the
driver of the chromosome because it is responsible for
the movement of chromosomes in mitotic spindle.
 The longitudinal half of chromosome is known as
Chromatid.
 The backbone of the chromosomal fibre is made up of
DNA molecule
Number of Chromosomes in Some
Organisms
Name (Animals)
Chromosome Numbers
Man (Homo Sapiens)
46
Dog (Canis Familiaris)
78
Cat (Felis Catus)
38
Rabbit ( Oryctolagus
Cuniculus)
44
Rat (Rattus norvegicus)
42
Mouse (Mus Muculus)
40
Frog (Rana Pipiens)
26
Cockroach (Blatta
Germanica)
23
Mosquito (Culex Pipiens)
6
Types of Cell Division
 Cell division involves the distribution of identical
genetic material – DNA – to two daughter cells
 It is well known that the DNA is passed along from one
generation of cells to the next
 A dividing cell duplicates its DNA - allocates the two
copies to opposite ends of the cell and afterwards split
into daughter cells.
Cell Division
 Cell division may occur by four methods:
a) Amitosis or direct cell division
b) Endomitosis
c) Mitosis
d) Meiosis
Amitosis or Direct Cell Division
 Amitosis is the means of asexual reproduction
 It happens in unicellular organisms like bacteria, yeast
etc.
 In this type the splitting of nucleus is followed by
cytoplasmic constriction
Endomitosis
 In this type, chromosomes duplicate but cytoplasmic
division is prevented.
 This results in the duplication of chromosome
number.
The Cell Cycle