Quiz next week on what we ve covered thru today!!!!!! Hour exam in 2 weeks!! Lab Practical in 3 weeks.

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1 Quiz next week on what we ve covered thru today!!!!!! Hour exam in 2 weeks!! Lab Practical in 3 weeks. Prepare your bones! Last week studied the bones of the skull, wrist, and ankle This week study, in addition to the skull, the axial skeleton. (Next week, study the appendicular skeleton) (after that, the fetal skeleton) Cell Theory The cell is the basic structural and functional unit of life Organismal activity depends on individual and collective activity of cells Biochemical activities of cells are dictated by their subcellular structures Continuity of life has a cellular basis Smooth endoplasmic reticulum Cytosol Lysosome Mitochondrion Centrioles Centrosome matrix Microvilli Chromatin Nucleolus Nuclear envelope Nucleus Plasma membrane Rough endoplasmic reticulum Ribosomes Golgi apparatus Cell Theory The Cell is the smallest living unit Disease is the loss of cellular homeostasis Over 200 cell types exist in the human body with sizes ranging from 2 um to 1 meter (nerve cell)! Shape (structure) reflects function. E.g. flat epithelial cells act as barriers for protection. Microfilament Secretion being released from cell by exocytosis Microtubule Intermediate filaments Peroxisome Figure 3.2 1

2 Cell Theory Cells are composed of three principle areas (regions) Plasma Membrane Cytoplasm Nucleus Plasma Membrane (Cell Membrane) Defines the extent of the cell Separates intracellular fluids from extracellular fluids Encloses all of the cell organelles Plays a dynamic role in cellular activity Plasma membrane is a double layer (bilayer) of lipids with imbedded, dispersed proteins A bilayer consists of phospholipids, cholesterol, and glycolipids Proteins are trapped in the bilayer: Extra/intracellular regions are hydrophilic Transdomain regions are hydrophobic The Lipids of the Bilayer Phospholipids have hydrophobic and hydrophilic bipoles Glycolipids are lipids with bound carbohydrate Cholesterol Membrane Structure The bilayer is self-orienting (forms by itself) -self assembly into spheres -seals quickly if torn The majority of the membrane lipids are unsaturated (phosphatidyl choline) which kinks the tails This Increases Membrane Fluidity!! Figure 3.3 2

3 Functions of Membrane Proteins Transport Intercellular adhesion Cell-cell recognition Attachment to cytoskeleton and extracellular matrix Transport Protein Enzymatic activity Functions of Membrane Proteins Enzymes Receptors for signal transduction Receptor Proteins Figure Plasma Membrane Surfaces Differ in the kind and amount of lipids they contain Glycolipids are found only in the outer membrane surface -5% of total membrane lipid 20% of all membrane lipid is cholesterol Figure Lipid Rafts Make up 20% of the outer membrane surface Composed of sphingolipids and cholesterol Create stable, less fluid, areas Are concentrating platforms for cell-signaling molecules -Polarization via the sugar group Structural Proteins -Wedges it rings between the phospholipid (nonpolar) tails -Increases fluidity of the membrane Membrane Proteins Two types: Integral & Peripheral Integral: Span the lipid bilayer Often are transmembrane proteins and protrude on both sides of the membrane Mainly involved in transport says your text book. WRONG!!!! Too general a statement 3

4 Peripheral Proteins Not embedded in the lipid bilayer Attach to integral proteins or membrane lipids Glycoproteins Proteins supporting sugar groups Includes many of the integral proteins that extend into the extracellular space Glycocalyx Carbohydrate rich area at the cell surface Formed from glycolipids and glycoproteins Useful in identifying cell types on the basis of the sugar types surrounding the cell Specializations of the Plasma Membrane: Microvilli Minute extensions & recessions of the plasma membrane that increase surface area Found on the surface of absorptive cells, e.g. intestine, kidneys, etc Have a core made of actin to support villi structure Membrane Junctions Bind cells together Factors include: Glycoproteins (e.g. adhesion proteins), Tight junction impermeable junction that encircles the cell Desmosome anchoring junction scattered along the sides of cells Gap junction a nexus that allows chemical substances to pass between cells Membrane Junctions: Tight Junction -Integral membrane proteins in the plasma membrane of adjacent cells that fuse together -Help prevent molecules from passing through the extracellular space between adjacent cells Figure 3.5a 4

5 Membrane Junctions: Desmosome Membrane Junctions: Gap Junction -Plaque on the cytoplasmic face of the plasma membrane -Adjacent cells are held together by cadherins (thin filaments) that extend from the plaques and interdigitate in the intercellular space like a zipper -Intermediate filaments form part of the cytoskeleton and extend from the plaques on the opposite sides of a cell (e.g. guy wires) -E.g. connexons: transmembrane proteins that form a hollow cylinder that connects adjacent cells -Varying connexons result in varying selectivity -Abundant in tissues subjected to great mechanical stress -Things like ions, sugars, and small molecules can pass Figure 3.5b Figure 3.5c Function of the Plasma Membrane Is bathed in Interstitial Fluid: Derived from blood Form of nutrition Baths the cells Contains: amino acids, sugars, fatty acids, vitamins, hormones, neurotransmitters, salts, waste Function of the Plasma Membrane Plasma membrane is a selective (or differentially) permeable barrier. E.g. allows some substances to pass and blocks others Plasma membrane moves things across by: Active processes: require ATP to cross P.M. Passive processes: require no energy from cell Passive Membrane Transport: Diffusion Diffusion is the tendency of molecules and ions to scatter evenly throughout the environment Molecules move from areas of high concentration to areas of low concentration Kinetic energy is the driving force. Thus, size and temperature influence rate of diffusion Passive Membrane Transport: Diffusion The plasma membrane is a physical barrier to free diffusion due to its hydrophobic core. Molecules will diffuse through the plasma membrane if the molecule is: lipid soluble can pass through membrane channels assisted by a carrier molecule 5

6 Passive Membrane Transport: Diffusion Simple diffusion nonpolar and lipid-soluble substances Diffuse directly through the lipid bilayer E.g. O 2 & CO 2 (opposite gradients), fat-soluble vitamins Passive Membrane Transport: Diffusion Facilitated diffusion Transported substance binds to protein carriers in the plasma membrane and is ferried across or moves through water filled protein channels E.g. sugars, amino acids, ions Diffuse through channel proteins Diffusion Carrier Proteins Are integral transmembrane proteins Show specificity for certain polar molecules, including sugars and amino acids, too large for simple diffusion and facilitated diffusion Molecules move down a concentration gradient Molecules are shielded from the hydrophobic plasma membrane by integral membrane proteins Channels Transmembrane proteins that transport ions & water through aqueous channels across the plasma membrane Pore size and net charge of the amino acids lining the channel determines selectivity Leaky channels: always open Gated channels: open & close by chemical or electrical signals Diffusion Through the Plasma Membrane Passive Membrane Transport: Osmosis Extracellular fluid Lipidsoluble solutes Lipid-insoluble solutes Small lipidinsoluble solutes Water molecules Occurs when the concentration of a solvent is different on opposite sides of a membrane Lipid Diffusion of water across a semipermeable membrane bilayer Osmolarity total concentration of solute particles in a solution Cytoplasm (a) Simple diffusion (b) Carrier-mediated facilitated (c) Channel-mediated (d) Osmosis, diffusion Tonicity how a solution affects cell volume directly through the diffusion via protein carrier facilitated diffusion through a specific phospholipid bilayer specific for one chemical; binding of substrate causes shape change in transport protein through a channel protein; mostly ions selected on basis of channel protein (aquaporin) or through the lipid [H 2 O] must be equal on both sides of membrane size and charge bilayer Osmosis Figure 3.7 6

7 Effect of Membrane Permeability on Diffusion and Osmosis Effect of Membrane Permeability on Diffusion and Osmosis [H2O] must be equal on both sides of membrane Figure 3.8a Figure 3.8b Effect of Membrane Permeability on Diffusion and Osmosis In a cell, however, as water diffuses into the cell, an equilibrium is reached where the hydrostatic pressure (back pressure exerted by the water against the membrane) within the cell is equal to its osmotic pressure Effect of Membrane Permeability on Diffusion and Osmosis Tonicity: the ability of a solution to change the shape or tone of a cell by altering its internal water volume Effects of Solutions of Varying Tonicity Isotonic solutions with the same solute concentration as that of the cytosol Hypertonic solutions having greater solute concentration than that of the cytosol Hypotonic solutions having lesser solute concentration than that of the cytosol RBC in Hypotonic Solution RBC in Isotonic Solution RBC in Hypertonic Solution Effects of Solutions of Varying Tonicity Thus, water moves towards greater solute concentration Water moves towards lesser water concentration Osmosis continues until osmotic and hydrostatic pressures acting at the plasma membrane are equal 7