IntroductionThe CellsThe OrganellesSummaryRevision exercises

Table of ContentsCell: The most basic unit of life.

1. introductionBasic building blocks of life

Smallest living unit of an organism

Grow, reproduce, use energy, adapt, respond to their environment

Many cannot be seen with the naked eye

A cell may be an entire organism or it may be one of billions of cells that make up the organism

The CellsThe E. coli Cell and animal CellProkaryotic cells Theyre small and simple, it grows and divides fast. It can adapt to rapid environmental changes. A single compartment with DNA and other biomolecules exist together in a well organized way.Extra-chromosomal DNA exists in the form of plasmid.Eukaryotic cells A hundred times larger, much more complexContain organelles to support different cellular functions from digestion to generation of energy and storage of nutrients.Extra-chromosomal DNAs exist in mitochondria and chloroplast.Differentiate to different cell-types.

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Every Eukaryotic cell has three main parts:

Plasma (cell) membrane - separates inside of cell from external environment.

Nucleus organelle that contains the cells DNA and is surrounded by a double membrane.

Cytoplasm everything from the nuclear membrane to the plasma membrane*

Cytoplasm refers to cytosol plus organelles and inclusions. cytosol - contains proteins, enzymes, nutrients, ions, and other small moleculesorganelles - highly organized structures with characteristic shapes that are specialized for specific cellular activities. inclusions - are temporary structures in thecytoplasm that contain secretions and storage products of the cell.

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Plasma membranePhysical isolationRegulation of exchange with the environmentSensitivity to the environmentSignal transductionStructural support*

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Membrane is fluid - fatty acid tails are unsaturatedThe membrane is selectively permeable it allows fat soluble substances to pass through (such as steroid hormones) and some other small, uncharged molecules.Cholesterol is a large molecule, and helps to stabilize the membrane.*

Membrane carbohydrates3-5 % of membraneProteoglycans, glycoproteins and glycolipidsGylcocalyxLubrication and protectionAnchoring and locomotionSpecificity in bindingRecognition

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Integral Proteins can be channels or transporters.Peripheral proteins can be receptors, enzymes or can be cell identity markers*

Intercelluar junctionsTight junctions membranes of adjacent cells bound together by occludins and claudins formingAn impermeable junction.

Desmosomes are protein spot welds in skin and cardiac muscle:plaques, linker protein filaments, and thicker filaments across inside of cell

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Intercellular junctionsGap junctions are tubular channels (connexons) that connect the cytoplasm of one cell with that of another.Ions, simple sugars and other small moleculesCellular Adhesion Molecules help cells form temporary attachments to other cells. CAMs

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Membrane proteinsAnchoring proteinsRecognition proteinsEnzymesReceptor proteins Ligands bindCarrier proteins allows establishment of electrochemical gradientChannelsRafts lipid rafts tails saturated; more cholesterol

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Membrane PhysiologyCell membrane function:Cellular communicationEstablish an electrochemical gradientAre selectively permeableLipidsSizeElectrical chargePresence of channels and transporters*

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Movement of materialsPassive processes:Depend on concentration and kinetic energyDo not require energyMove substances from an area of high concentration to an area of low concentrationDown a concentration gradient*

DiffusionRate depends on:TemperatureGradient sizeDistance Molecule sizeElectrical forcesReaches equilibrium orPhysiological steady state*

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Simple diffusionChannel mediated diffusion0.8 nm Size and charge Interaction between ion and channel wallsRate limited by number of suitable channels- Na, K, Cl pass through membranes at a rate comparable to simple diffusion*

OsmosisMovement of WATER through a selectively permeable membraneMoves according to the conc. of waterOsmotic pressure*

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TonicityConcentration of one solution relative to another ( conc. in cytoplasm)Isotonic equal concentrations0.9 % NaCl or 5% glucose soln.Hypertonic more concentratedHypotonic less concentrated*

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osmosisEliminates conc. differences faster than solute diffusionAquaporins - water channels

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Facilitated diffusionUses carrier moleculesDown a conc. gradientSpecificitySaturation limitsregulation*

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Filtration-a type of bulk flow where the movement of water and dissolved substances across a membrane is due to gravity or hydrostatic pressure (water pressure).*

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Active TransportDepends on the use of energy (ATP)Moves substances up a concentration gradient (up hill)These systems are often called pumpsNa+ / K+ pump - Na/K ATPaseOthers carry Ca++, Mg++, I-, Cl- and Fe++*

Active transportCountertransportExchange pumpCotransport or symportMove two different substances in same directionOne down a conc. GradientUse of energy to pump one substance back out*

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Vesicular TransportExocytosis moving substances outside the cellEndocytosis taking substances into the cell clathrin proteinsPinocytosis cell drinkingPhagocytosis cell eatingReceptor mediated endocytosis*

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Receptor mediated endocytosis*

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Exocytosis*

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