cell and its constituents
TRANSCRIPT
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A TOUR OF THE CELL
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Dr.Bhavna Tyagi(PG 1ST year)
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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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Cell cycleMitosis and MeiosisCheckpoints in cell cycle Apoptosis
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history
Robert Hooke used simple lenses to observe cork in which he saw tiny compartments he called cells (cellulae)
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What is a cell?5
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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
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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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Difference between prokaryotic and eukaryotic
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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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Basic aspectsStructural 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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• 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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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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Thin, pliable, elastic structure
only 7.5 to 10 nm thickComposed entirely of proteins
and lipidsAppears to be trilaminar in
electron microscope.
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Components of membrane
Lipid bilayerCholesterolCarbohydratesProteins
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Fluid mosaic model of membrane 15
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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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PHOSPHO LIPID MOLECULE
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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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PROTEIN MOLECULES2 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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FUNCTIONS OF TRANSMEMBRANE PROTEIN
CELL TO CELL adhesionCELL MATRIX adhesionFormation of pores or channels for the
transport of materials into and out of the cell
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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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Cytoplasm and its organelles
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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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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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Types of Organelles
Nonmembranous organelles: no membranedirect contact with cytosol
Membranous organelles: covered with plasma membraneisolated from cytosol
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Membranous Organelles
Endoplasmic reticulum (ER)Golgi apparatusLysosomesPeroxisomesMitochondria
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Non membranous organelles
Ribosomes (free ribosomes and polysomes)Microtubules Centrioles Cilia and flagellaFilaments
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THE NUCLEUS
Discovered by Robert Hooke in 1831
Is the cell’s control center
Contains DNA: genetic material
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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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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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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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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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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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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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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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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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Endoplasmic Reticulum CONT.
Cisternae are storage chambers within membranes
2 types:
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
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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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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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Smooth Endoplasmic Reticulum
No ribosomes attached
Tubular Membrane
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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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Function of sER
GLYCOGEN SYNTHESIS
LIPID AND STEROID SYNTHESIS
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FUNCTION OF rER
Site for protein synthesis
Help in transport of protein
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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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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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FUNCTIONS
Formation of cell wallSynthesis of glycolipidLysosomes formationWater balanceLipid secretionProtein secretion
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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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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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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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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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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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Peroxisomes53
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MITOCHONDRIA
Power house of the cell.
Present in all areas of the cell’s cytoplasm.
Variable in size n shape
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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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The cytoskeleton
Cytoskeleton: Supporting framework
Three main types : microfilament, microtubules and intermediate filament
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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 cytoplasmAttach integral proteins to cytoskeletonPairs with thick filaments of myosin for muscle
movement
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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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Thick Filaments
15 nm diameter Composed of myosin Muscle cells only
FunctionInteract with actin to produce movement
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Microtubules
Large (25nm diameter), hollow tubes
Composed of tubulin protein
Originate from centrosome
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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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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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Cilia and Flagella
Hair like projections
Contain a microtubule core with cytoplasm covered in plasma membrane
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Cilia: Short, numerousFunction: sweep substances over cell surface
Flagella: Long, singularFunction: propel cell through environment
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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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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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phagocytosis 67
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Pinocytosis (cell drinking) Endosomes “drink” extracellular fluid
and enclose it in membranous vesicles at the cell surface
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Mitosis and MeiosisCell cycleCheckpoints in cell cycle ApoptosisThese topic will be cover in next seminar
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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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THANK YOU
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Cell cycle and replication
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cell cycleProliferating cell progress
through a series of checkpoints and defined phases called THE CELL CYCLE
CELL CYCLE consists of G1,S,G2,M,G0 phases
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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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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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Mitosis
What is the purpose of mitosis?
Cell division
Products genetically identical
Growth of organism
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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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Divided into
Prophase
Metaphase
Anaphase
Telophase
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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.
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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.
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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.
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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
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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.
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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
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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
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Meiosis
FunctionReduction division (23 chromosomes per gamete)
MechanismEach 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
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Meiosis IntroductionMeiosis consist s of two successive
divisions called the first and the second meiotic divisions
1st meiotic division
Prophase is prolonged
Divided into 4 stages
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Meiosis I Fig A represents leptotene stage-chromosomes become visible consist 2 chromatids ,cnt distinguish
Fig B represents zygotene stage-pairing of chromosome called synapsisThe two chromosomes together c/a bivalent
Fig C represents pachytene stage -4 chromatid visible c/a tetrads,2 central and 2 peripheral chromatids.Cont..
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Fig D cont. pachytene stage-2 central chromatid cross over c/a crossing overThe 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
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Nuclear membrane disappear Spindle has formedChromosomes attach to the spindle at equatorChromosome attach by centromere
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One entire chromosome of the pair moves to either poleNOTE that the centromere does not divide
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Similar to mitosisNOTE that the chromosome in each cell have been reduced to half the diploid number
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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
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Regulation of cell cycle
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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
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Cyclins and Cyclins –Dependent Kinases
Phosphorylation 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
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Cell cycle inhibitor
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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
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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
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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
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Regulation of cell cycle
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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.
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(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 .
causes
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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
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MECHANISM
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Regulation
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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