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The Cell By Dr.Hikmat Fatima HashmiobjectivesWhat is the cell.Types of cells.Deep detail about cell.Cell and its organelle.Structure and function of cell organelles.Diagrams showing detail structures of organelleSelf assessment at the end of classCellCell is the basic structural and functional unit of life.

Unicellular organisms are capable of:Independent existence Performing essential functions of life

Discovered by Anton Von Leeuwenhoek

CELL THEORYMatthias Schleiden and Theodore Schwann proposed that all living things are made up of cells but didnt say where cells came from.Rudolf Virchow modified this theory:

All living organisms are composed of cells and products of cells.All cells arise from pre-existing cells.Visualising cellsCells are small because a high surface area-to-volume ratio is essential.To see them, we use microscopes having good magnification & resolution.

PROKARYOTIC CELLSingle-celled organisms that lack a membrane-bound nucleus, and any membrane-bound organelles.Bacteria and Archaea are prokaryotes. They dont have a well organized nucleus. DNA is in nucleoid.They have a plasma membrane and cytosol.They can live on a diversity of energy sources and some can tolerate extreme conditions.Mesosome is an infolding of cell membrane to increase surface area.

EUKARYOTIC CELLIs characterized byPresence of membrane bound organelles.Organised nucleus with nuclear envelopesPlant cells have cell walls.Animal cells have centrioles.Compartmentalization is the key to eukaryotic cell function. Each organelle or compartment has a specific role defined by chemical processes.CELL

Now lets go deep inside a cell.We will study nextPlasma membraneRibosomesEndoplasmic ReticulumGolgi ApparatusLysosomesvacuolesMitochondriaPlastides

CenteriolesCentrosomes NucleusTypes of choromosomes

PLASMA MEMBRANE- the outer surface of every cellSTRUCTURE:Composed of lipids arranged in a phospholipid bilayer. There are also proteins and carbohydrates.Lipids have polar head towards outerside and hydrophobic tails towards inside, so that tails are protected from aqueous envt. 2 types of proteins: Peripheral and Integral.Fluid mosaic model: Quasi-fluid nature of lipid enables lateral movement of proteins.(there is constant motion)

PLASMA MEMBRANEFUNCTIONS:Cell growthCell divisionTransport of materialsCell Membrane: Selectively permeableTypes of Transport:Passive Transport: Without energy requirementOsmosis: Movt. Of water moleculesActive transport: With energy requirementAgainst concentration gradient Eg: K+, Na+ pump

PLASMA MEMBRANEFUNCTIONS:Is a selectively permeable barrier. Allows cells to maintain a constant internal environment.Is important in communication and receiving signals.Often has proteins for binding and adhering to adjacent cells.ENDOMEMBRANE SYSTEMConsists of the following organelles:

ENDOMEMBRANE SYSTEMThe endomembrane system includes the plasma membrane, nuclear envelope (outer membrane), endoplasmic reticulum, Golgi apparatus, and lysosomes.

The endomembrane system and cell nucleus may have originated from the inward folds of plasma membrane of prokaryotes.

RIBOSOMESRibosomessites of protein synthesis.Occur in both prokaryotic and eukaryotic cells.Consist of ribosomal RNA (rRNA) and more than 50 different protein molecules. Ribosomes are not organelles.In eukaryotes, ribosomes are free in the cytoplasm, attached to the ER, or inside mitochondria and chloroplasts.ENDOPLASMIC RETICULUM (ER)Network of interconnected membranes in the cytoplasm.2 types of ER:Rough Endoplasmic Reticulum (RER):Ribosomes attached to surfaceActively involved in protein synthesis

Smooth Endoplasmic Reticulum (SER):No Ribosomes attached to surfaceActively involved in lipid synthesis and steroidal hormones.

GOLGI APPARATUSComposed of Flat, disc shaped sacs called cisternae and membrane enclosed vesicles.Cisternae are stacked parallel to each other2 faces: CIS and TRANS face.Functions:Packaging and delivery of materialMaterials are packaged from ER into vesicles fuse with the CIS face and move towards TRANS face.Forms glycoproteins and glycolipids.Primary lysosomes originate from the Golgi.

LYSOSOMESFormed in Golgi apparatusVescicular StructuresSuicide bags of the cellThey contain enzymes that digest the cell and cause the cell to die.

VACUOLES Space inside cytoplasm covered by membrane called tonoplastStorage house of cellContains water, cell sap, excretory products, etc{rpvides structure for plant cells.Amoeba: Contractile vacuole (excretion)Protists: Food vacuole (engulfing food)

MITOCHONDRIAPower house of the cellStructure:Sausage-shaped and cylindricalDouble membrane: Inner and outerIn the space of inner membrane (inner compartment) is called matrix. Inner membrane has infoldings called cristae (increases surface area)Outer compartment is the limiting boundary.

MITOCHONDRIAPower house of the cellFunction:Site for aerobic/cellular respiration.Produce cells energy in the form of ATPThey have their own DNA and ribosomesplastidsOccur only in plants and some protists.Chloroplasts: Site of photosynthesis light energy is converted to the energy of chemical bonds.

CENTROSOME & CENTRIOLESCentrosome contains 2 cylindrical structures called centrioles.Organized like a cartwheel9 peripheral triplet protein fibrilsCentral protein hubHub connected to peripheral proteins by radial spokes.Centrioles form spindle fibres during cell division.

NUCLEUSContains the DNA Site of DNA replicationSite where gene transcription is turned on or offAssembly of ribosomes begins in a region called the nucleolus

NUCLEUS (NOT DIVIDING)Inside it is: very coiled fibres called chromatin (DNA)Space inside nucleus is nuclear matrix (nucleoplasm)Spherical bodies called nucleoli (for RNA synthesis)

NUCLEUS (NOT DIVIDING)Covered by nuclear envelope which has two membranes:Inner membraneOuter membrane (with ribosomes)Space between them is perinuclear space Nuclear pores are pores on the membrane controlling movement of substances.

Nuclear lamina proteins attaches to both the chromatin and the nuclear envelope and maintains nuclear shape.

NUCLEUS (DIVIDING)Chromatin ChromosomesEvery chromosome has a constriction called centromere At the sides of centromere are kinetocores

METACENTRIC CHROMOSOMECentromere in middle2 equal arms

SUB-METACENTRICCentromere slightly away from middleOne shorter and one longer arm

ACROCENTRICCentromere close to the end of chromosomeOne very long and one very short arm

TELOCENTRICTerminal centromere

cytoskeletonSupports and maintains cell shapeHolds organelles in positionMoves organellesThe cytoskeleton has three components:MicrofilamentsIntermediate filamentsMicrotubules

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