Introduction1665 Robert Hooke inspected thin slices of cork and found they consisted of millions of small, irregular unitsThis research produced the cell theoryCells are building blocks of all plants and animalsAll cells come from division of preexisting cellsCells are smallest units that perform all vital physiological functionsEach cell maintains homeostasis at cellular levelCytology- the study of cellular structure and function; part of cell biology- integrates aspects of biology, chemistry and physicsTwo general classes of cells:1. Sex cells (germ/reproductive cells)-are either the sperm of males or oocytes of females2. Somatic cells- include all other cells in human body3.1: Plasma MembraneThe plasma membrane separates the cell from its surrounding environment and performs various functionsExtracellular Fluid (Interstitial Fluid):A watery medium that surrounds a cellPlasma membrane (cell membrane) separates cytoplasm (inside of cell) from extracellular fluidCytoplasm – region of cell found between the plasma membrane and the nuclear membraneCytosol – liquid component of the cytoplasmOrganelles – Intracellular structuresPlasma Membrane - outer boundary of a cell, also called cell membraneFunctions of the Plasma Membrane:1. Physical isolation - physical barrier that separates inside of cell from surrounding extracellular fluid2. Regulation of Exchange with Environment - plasma membrane controls entry of ions and nutrients, eliminations of wastes and release of secretions3. Sensitivity to Environment - first part of the cell affected by changes in the composition, concentration or pH of extracellular fluidContain receptors that allow cell to recognize & respond to specific molecules in environment4. Structural Support - specialized connections between plasma membrane, or between membranes and extracellular materials give tissues stabilityCharacteristics of the Plasma Membrane:Plasma membrane is extremely thinComposed Of:1. Lipids2. Proteins3. CarbohydratesMembrane Lipids – form most of the surface area of the plasma membrane but only make up 42% of its weightPlasma membrane is called the Phospholipid bilayer (phospholipid molecules in it form two layers)Has hydrophilic end (phosphate portion) and hydrophobic end (lipid portion)In each half of bilayer, lie with hydrophilic heads at membrane surface and hydrophobic tails in insideAlso contains cholesterol and small quantities of other lipidsWater and solutes cannot cross the lipid portion of the plasma membraneMembrane proteins - account for about 55% of weight of plasma membraneIntegral Proteins - part of membrane structure and cannot be removed with damaging/destroying the membraneMost span the width of the membrane one or more times, therefore known as transmembrane proteinsGreatlyPeripheral proteins – bound to inner or outer surface of the membrane and easily separated from itDifferent types of Functional Proteins:1. Anchoring Proteins - attach plasma membrane to other structures and stabilize its positionInside cell, membrane proteins are bound to the cytoskeletonOutside the cell, other membrane proteins may attach cell to extracellular protein fibers or to another cell2. Recognition Proteins (identifiers) - cells of immune system recognize other cells as normal or abnormal based on presence or absence of characteristic recognition proteins3. Enzymes - may be integral or peripheral; catalyze reactions in extracellular fluid or in cytosol, depending on location of the protein and its active site4. Receptor Proteins - sensitive to the presence of specific extracellular molecules called ligandsExtracellular ligand will bind to appropriate receptor, causing changes in the activity of the cell5. Carrier Proteins - bind solutes and transport them across the plasma membraneMay require ATP as energy source6. Channels - some integral proteins contain a central pore or channel that forms a passageway across the plasma membranePermits movement of water and small solutes across plasma membraneMany are highly specific and permit passage of only one ionMembrane Carbohydrates – account for about 3% of weight of plasma membrane; components of complex molecules such as proteoglycans, glycoproteins and glycolipidsCarbohydrates of these molecules extend beyond outer surface of membrane forming layer known as the glycocalyx which has the functions of:Functions of Glycocalyx:1. Lubrication and Protection - glycoproteins and glycolipids form a viscous layer that lubricates and protects plasma membrane2. Anchoring and Locomotion - help anchor cell in place due to stickiness/takes part in locomotion of specialized cells3. Specificity in Binding - glycoproteins and lipids can function as receptors, binding specific extracellular compounds4. Recognition - body’s immune system recognizes its own membrane glycoproteins and lipids as self rather than foreign, keeping immune system from attacking own cells while still recognizing invading pathogens3.2: Cell OrganellesOrganelles within the cytoplasm perform particular functionsCytoplasm - general term for the material located between the plasma membrane and membrane surrounding nucleusContains more proteins than the extracellular fluidContains cytosol - intracellular fluid, contains dissolved nutrients, ions, soluble and insoluble proteins and waste productsContains organelles - structures suspended within cytosol that perform specific functions for the cellThe Cytosol:Cytosol is different from extracellular fluid:Concentration of potassium ions is much higher in cytosol; concentration of sodium ions is lower in cytosolCytosol contains higher concentration of suspended proteins, many being enzymes that regulate metabolic operations, others associated with various organellesConsistency of cytosol determined largely by enzymes and cytoskeletal proteinsCytosol contains small amounts of carbohydrates, small reserves for amino acids and for lipids; extracellular fluid is a transport medium only, and no reserves are stored thereThe Organelles:Organelles - internal structures that perform most of the tasks that keep a cell alive and functioning normallyNon-membranous-not completely enclosed by membranes and all their components are in direct contact with cytosolCytoskeleton, microvilli, centrioles, cilia, ribosomes, proteasomesMembranous-isolated from cytosol by phospholipid membranes, just as plasma membrane isolates cytosol from extracellular fluidEndoplasmic reticulum, Golgi apparatus,
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