Lesson 2 The Cell and the Plasma Membrane Cell Theory Developed from Robert Hooke s research Cells are the building blocks of all plants and animals All cells come from the division of preexisting cells Cells are the smallest units that perform all vital physiological functions Each cell maintains homeostasis at the cellular level Cytology the study of cells Two general classes of cells in the human body o Somatic Cells All body cells except sex cells o Sex Cells germ cells or reproductive cells Reproductive cells Male sperm Female oocyte a cell that develops into an egg Cilia are long extensions containing microtubule doublets Function Movement of material over cell surface Microvilli Membrane extensions contain microfilaments Function Increase surface area to facilitate absorption of extra cellular materials Proteasomes Hollow cylinders of proteolytic enzymes with regulatory proteins at their ends Function Breakdown and recycling of damaged or abnormal intracellular proteins Ribosomes RNA proteins fixed ribosomes bound to rough endoplasmic reticulum free ribosomes scattered in cytoplasm Function Protein synthesis Cytoskeleton Proteins organized in fine filaments or slender tubes Function Strength and support movement of cellular structures and materials Plasma Membrane Lipid bilayer containing phospholipids steroids proteins and carbohydrates Function Isolation protection sensitivity support controls entry and exit of materials Extracellular Fluid Interstitial Fluid A watery medium that surrounds a cell Plasma membrane cell membrane separates the inside of the cell cytoplasm from the extracellular fluid Cytoplasm inside of the cell Cytosol liquid component of the cytoplasm Intracellular structures collectively known as organelles Four General Functions of the Plasma Membrane 1 Physical Isolation Physical barrier separating the inside of the cell from the outside environment 2 Regulation of Exchange with the Environment Can regulate Entry of ions and nutrients Release of wastes cellular products released 3 Sensitivity to the Environment Extracellular fluid composition can alter plasma membrane Can detect chemical signals through plasma receptors proteins 4 Structural Support Anchors cells and tissues to each other or the extracellular matrix provides stability to cells The plasma membrane is composed of 1 Membrane Lipids largest component consists of Phospholipid bilayer two layers of phospholipids Hydrophilic heads toward watery environment both sides Hydrophobic fatty acid tails inside membrane away from water The bilayer forms a barrier to ions and water soluble compounds Note ions and H2O soluble compounds cannot move past the hydrophobic lipid tails 2 Membrane Proteins second largest component of the plasma membrane but 55 of the weight of the plasma membrane Two general classes 1 Integral Membrane Proteins Found embedded within the membrane If it traverses the width of the plasma membrane it is a transmembrane protein 2 Peripheral Membrane Proteins Bound to inner or outer surface of the plasma membrane Less numerous than integral proteins 3 Membrane Proteins may have different functions 1 Receptor Proteins Bind and respond to ligands ions hormones Binding of the ligand can cause a change within the cell 2 Carrier Proteins Transport specific solutes through membrane May or may not require energy ATP Ex Glucose transport does not require energy but Na and Ca2 transport does 3 Channels integral protein that has a central pore Regulate water flow and solutes through membrane Many channels are highly Attach to inside cytoskeletal or outside extracellular protein fibers or another specific for a specific ion 4 Anchoring Proteins stabilizers cells structures Stabilizes the cell 5 Recognition Proteins Identifiers Label cells as normal or abnormal prevents immune system from reacting to the cell Many recognition proteins are glycoproteins 6 Enzymes may be integral or peripheral proteins Catalyze reactions inside or outside the cell Note about membrane proteins may be located at specific locations on the cell inside leaf or outside leaf 4 Membrane Carbohydrates 1 Proteoglycans glycoproteins and glycolipids Extend outside cell membrane Form sticky sugar coat glycocalyx Functions of the glycocalyx include 1 Lubrication and Protection of plasma membrane 2 Anchoring and Locomotion 3 Specificity in Binding receptors function as receptors 4 Recognition immune response indentifiers that are genetically determined 2 Permeability determines what moves in and out of a cell and a membrane that 5 Membrane Transport 1 The plasma cell membrane is a barrier but Nutrients must get in Products and wastes must get out Lets nothing in or out is impermeable Lets anything pass is freely permeable Restricts movement is selectively permeable selectively permeable Plasma membrane is Allows some materials to move freely Restricts other materials Selective permeability restricts materials based on Size of the material Electrical charge Molecular shape Lipid solubility Membrane Transport Transport through a plasma membrane can be Active requiring energy ATP Passive no energy required Types of transport include Diffusion passive Carrier mediated transport passive or active Vesicular transport active Diffusion All molecules are constantly in motion Molecules in solution move randomly Random motion causes mixing Concentration of a solution is the amount of solute dissolved substance in a solvent liquid component The difference between the solute at one area compared to another creates a concentration gradient a potential energy gradient Factors Influencing Diffusion Distance the particle has to move Molecule Size Smaller is faster Temperature More heat faster motion Concentration Gradient Electrical Forces Opposites attract like charges repel Diffusion across Plasma Membranes Can be simple or channel mediated The difference between high and low concentrations the greater the difference the faster the diffusion Materials that diffuse through plasma membrane by simple diffusion Substances that can cross the lipid by simple diffusion layer include Lipid soluble compounds alcohols fatty acids and steroids Dissolved gases oxygen and carbon dioxide Channel mediated diffusion through a channel in a transmembrane proteins Water soluble compounds and ions Factors in channel mediated diffusion Size Charge Interaction with the channel leak passive channels Osmosis A Special Case of Diffusion Osmosis is the diffusion of
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