Lesson 2 Cell Theory Developed from Robert Hooke s Research viewing cork under light microscope 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 study of cells Two classes of cells in human body o Somatic body cells not sex cells o Sex cells germ cells or reproductive cells Male sperm Female oocyte cell that develops into an egg Extracellular fluid Interstitial Fluid watery medium that surrounds a cell plasma membrane separates inside from ECF o cytoplasm region of cell between plasma membrane and nuclear membrane o cytosol liquid component of the cytoplasm o organelles intracellular structures Four General Functions of the Plasma Membrane 1 physical isolation a separates inside from outside 2 regulation of exchange with the environment regulates entry of ions and nutrients release wastes through exocytosis a b 3 sensitivity to the environment a ECF can alter plasma membrane b Can detect chemical signals through plasma receptors proteins 4 Structural support a anchors cells and tissues to each other or to the Extracellular matrix b stability The plasma Membrane is composed of Membrane Lipids Proteins and Carbohydrates Membrane lipids are the largest component They consist of o Phospholipid bilayer 2 layers of phospholipids that forms a barrier to ions and water soluble compounds membrance Hydrophilic heads moves toward watery environment on both sides Hydrophobic tails fatty acids move away from watery environment inside Ions and water soluble compounds cannot move past the hydrophobic lipid tails This allows for cell interior to have a different composition that the extracellular environment Membrane Proteins 2nd largest component but 55 of the weight of the plasma membrane because they are heavier than lipids o 2 classes of membrane proteins Integral embedded within the membrane if it traverses the width of the membrane it is considered a transmembrane protein more numerous than peripheral Peripheral bound to inner or outer surface of membrane less numerous than o 6 functions of membrane proteins located either at specific locations inside leaf or integral outside leaf Receptor proteins Carrier proteins Channels bind and respond to ligands ions hormones which can cause change within a cell transport specific solutes through the membrane may or may not require ATP energy glucose transport does not require energy Calcium and Sodium ions do integral proteins with a central pore regulate water flow and solutes through the membrane highly specific for a specific ion extremely important in nerve impulse conduction and muscle contraction anchoring proteins attach to inside or outside structures stabilize the cell recognition proteins identifiers many are glycoproteins enzymes integral or peripheral catalyze reactions inside or outside label cells as normal or abnormal to prevent the immune system from reacting to the cell Plasma Membrane is selectively Permeable Allows some materials to move freely o Restricts other materials o Selective permeability restricts materials based on Size of the material Electrical charge Molecular shape Lipid solubility correlation between drug potency and lipid solubility Ex Anesthetics such as chloroform ether Membrane Transport is either active requires ATP energy or passive no energy Required Types of transport o Diffusion passive o Carrier mediated passive or active o Vesicular active Diffusion All molecules constantly in motion Molecules in solution move randomly Random motion causes mixing Concentration amount of solute in a solvent o Difference between solute in two areas creates concentration gradient potential energy gradient Note during diffusion of multiple substances treat the diffusion of each substance as if it was the only substance present Factors influencing diffusion o Distance particle has to move o Molecule size smaller faster o Temperature more heat faster o Concentration Gradient the greater the difference between high and low concentration the faster o Electrical forces opposites attract like charges repel Diffusion across Plasma Membranes o Simple or channel mediated Simple materials that diffuse through plasma membrane Lipid soluble compounds alcohols fatty acids steroids Dissolved gases Channel Mediated through channel in transmembrane proteins for water soluble compounds and ions Factors o Size o Charge o Interaction with the channel leak passive channels o Passive channels always open and allow passage in either direction from higher to lower concentration Osmosis A Special Case of Diffusion o Osmosis is the diffusion of water across the cell membrane For osmosis to occur Membrane must be freely permeable to water selectively permeable to solutes solutes Water molecules diffuse across membrane toward solution with more More solute molecules lower concentration of H2O molecules As H2O moves to that side the volume increases on the side with more solutes to dilute it to the same concentration as the concentration on the other side Osmolarity and Tonicity o The osmotic effect of a solute on a cell Two fluids may have equal osmolarity total solute concentration but different tonicity effect of the osmotic solution on cells o Isotonic iso same tonos tension A solution that does not cause osmotic flow of water in or out of a cell Has less solutes and loses water through osmosis Has more solutes and gains water by osmosis o Hypotonic hypo below o Hypertonic hyper above o A cell in a hypotonic solution Gains water o A cell in a hypertonic solution Loses water A cell will shrink Ex crenation of red blood cells If left unchecked it will ruptures Ex hemolysis of red blood cells Carrier Mediated Transport moves ions and organic substances Characteristics o Specificity o Saturation limits o Regulation Types o Cotransport o Countertransport One transport protein one set of substrates Rate depends on transport proteins not substrate Cofactors such as hormones A k a symport Two substances move in same direction at same time One substance moves in while another moves out Facilitated diffusion if the carrier mediated transport does not use energy o Transports molecules too large to fit through channel proteins glucose amino acids o Molecule binds to receptor site on carrier protein Receptor site is specific to certain molecules o Protein changes
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