Lecture Delivered at KMC – IC 3 October 2011. Format of Lecture Introduction on Cell Cycle Concept...
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Transcript of Lecture Delivered at KMC – IC 3 October 2011. Format of Lecture Introduction on Cell Cycle Concept...
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Lecture Delivered at KMC – IC3 October 2011
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Format of LectureIntroduction on Cell CycleConcept of Cell DivisionTypes of Cell DivisionRole of Chromosomes in Cell DivisionMitosis: Technical CharacteristicsMeiosis: Technical CharacteristicsOverall Learning Outcome
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Introduction on Cell CycleDistinction between Living and Non-Living
mattersLiving things reproduce and they have a capacity
to procreateProcreation in the living organism has a cellular
basisA 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
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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
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Postulates of Cell CycleAll living organisms are composed of cells
and cell productsThere 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
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Structural Types of CellProkaryotic 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.
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Difference Between Prokaryotic and Eukaryotic CellsProkaryotic Cella)Nuclear membrane
absentb)Nucleolus absent c)Lack of clearly
defined membranesd)Mitotic apparatus
absente)Nucleus diffused or
incipient
Eukaryotic Cella)Nuclear membrane
is presentb)Nucleolus is also
presentc)Chromosomes are
made up of DNAd)Mitotic apparatus
presente)Nucleus is well
organised
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Biological Organisation of ProtoplasmProtoplasm is bounded by a cell membrane. It is
further divisible into cytoplasm and nucleoplasmNucleoplasm is enclosed by the nuclear
membraneThe 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
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Concept and Key Roles of Cell DivisionCell Division plays several important roles in
the life of an organismTo 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.
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Continued:Without Cell division, multicellular organisms
cannot growWhen 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.
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Continued:Cell division continues to function in renewal
and repairIt replaces cells that die from normal wear
and tear or accidents.Cell division process is an integral part of the
cell cycleHow cell division distributes identical genetic
material to daughter cellsUnderstanding of the cellular mechanics of
cell division is very essential for a scholar
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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.
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Role of Chromosomes in Cell DivisionA chromosome is a body having special
organisation, individuality and functional qualitiesIt is capable of reproducing itself through
successive cell divisionsThere 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
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ChromosomesThe 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
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Name (Animals) Chromosome Numbers
Man (Homo Sapiens) 46Dog (Canis Familiaris) 78Cat (Felis Catus) 38Rabbit ( Oryctolagus Cuniculus)
44
Rat (Rattus norvegicus) 42Mouse (Mus Muculus) 40Frog (Rana Pipiens) 26Cockroach (Blatta Germanica)
23
Mosquito (Culex Pipiens)
6
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Types of Cell DivisionCell 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.
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Cell DivisionCell division may occur by four methods:a)Amitosis or direct cell divisionb)Endomitosisc)Mitosisd)Meiosis
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Amitosis or Direct Cell DivisionAmitosis is the means of asexual
reproductionIt happens in unicellular organisms like
bacteria, yeast etc.In this type the splitting of nucleus is
followed by cytoplasmic constriction
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EndomitosisIn this type, chromosomes duplicate but
cytoplasmic division is prevented.This results in the duplication of chromosome
number.
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