BIO 3324 1nd Edition Lecture 1 Outline of Last Lecture I. IntroductionOutline of Current Lecture II. Fluid compartments III. Plasma MembraneIV. Channel proteinsV. Mass balanceVI. Law of diffusion Current LectureThe three fluid compartments of the body:• Body can be divided into two primary compartments: Cells & Fluid – ICF (intracellular fluid) - fluid that is found inside the cells– ECF (extracellular fluid) – fluid that is found outside the cells• Compartments are separated by a barrier - Cell Membrane• ECF is further divided by a “Wall” that separates fluid that circulates and that which directly surrounds the cells– Plasma – fluid portion of the blood– Interstitial fluid – fluid that surrounds the cellsThe Plasma Membrane:• AKA , the cell membrane or Plasmalemma • Functionally responsible for:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.– Physical isolation – acts as a physical barrier between the contents of the cell and the surrounding environment– Regulation of exchange of materials – controls the removal of waste, the entry of nutrients and ions, & the release of cellular products– Communication between the cell & its environment – proteins found within the membrane enable the membrane to monitor changes in the environment and respond tomolecular signals– Structural support – proteins serve as a cytoskeleton maintaining cell shape, creating specialized junctions between cells and the extracellular matrix thus stabilizing cells within tissues.The Fluid Mosaic Model:• Membranes consist mostly of Lipids and Proteins– Ratio is dependent on the source but correlates to metabolic activity (↑ metabolic activity = ↑ proteins)• The lipid portion consists mostly of phospholipids arranged in a bilayer– Hydrophilic heads face the aqueous side– Hydrophobic tails are hidden in the center of the membrane• Proteins can be found embedded in or attached to either surface of the membraneThree types of lipids in the Plasma Membrane:• Phospholipids – Polar phosphate/glycerol head (hydrophilic)– Non-polar fatty acid tail (hydrophobic)• Sphingolipids – possess fatty acid tails but head can be either a Phospholipid or a Glycolipid (Sugar Chain)• Cholesterol – Very hydrophobic– Insert themselves in the plasma membrane– Helps makes the plasma membrane impermeable to water-soluble molecules– Allows for flexibility over wide temperature rangesMembrane Lipids serve as a barrier:• In an aqueous environment phospholipids arrange themselves so that the polar heads face theaqueous environment and the non-polar tails hide from the aqueous environmentThree types of Membrane Proteins:• Integral, AKA, Transmembrane proteins– Extend across the membrane– Possess hydrophobic segments that anchor it in the membrane– Classified by the number of Transmembrane segments they possess– Extracellular & Intracellular loops are available for interaction with other proteinsand/or molecules– Some are anchored to Cytoskeletal proteins making them immobile• Peripheral proteins– Attached loosely to the integral proteins or polar heads of the lipids– Include enzymes & structural binding proteins• Lipid-anchored proteins– Covalently bound to fatty acid tails and found inserted in the bi-layer– Usually associated with Sphingolipids forming lipid raftsMembrane Carbohydrates:• Sugar chains attached to either a membrane protein (Glycoprotein) or a Lipid (Glycolipid)• Found only on the external surface of a cell• Serve as highly specific biological markers that help cells identify other cells• The Glycocalyx is a protective layer of membrane bound sugarsThe Law of Mass Balance:• The body is an open system that exchanges heat and materials with the outside environment• A primary function of the body is the maintenance of Homeostasis – a constant InternalEnvironment• Functions on the principle of Mass Balance– For any amount of substance in the body to remain constant, any gain must be offset byan equal loss– Gain = intake (via food and drink) as well as materials produced– Loss = usually accomplished through excretion (think urine, feces, exhaling, sweating)but also through metabolism (catabolic activity to break down & anabolic to makesomething new)Homeostasis ≠ Equilibrium:• Homeostasis refers to the stability of the body’s internal environment (e.g. the ECF & ICF)– While these compartments are relatively stable in terms of composition they differ from one another in terms of concentrations of solutes– As a result there are concentration gradients between the two compartments• Our bodies are in a state of osmotic equilibrium (total amount of solute per volume of fluid on either side of the cell membrane) but are in a state of chemical disequilibrium (certain solutes are more concentrated in one of the two compartments)• Our bodies are electrically neutral, but as result of ionic imbalances are in a state of electrical disequilibrium• This osmotic equilibrium and chemical & electrical disequilibrium are dynamic steady states– Dynamic meaning that the substances are constantly moving back and forth between the two compartments– Steady state meaning that there is no net change or net movement between the two compartments• This is accomplished by transport mechanisms and selective permeability of the membraneBulk flow:• Pressure gradients causes fluids to flow from a region of higher pressure to a region of lower pressure• All the components of the fluid moves En Masse• Examples:– Circulatory system– Respiratory systemMembrane Permeability:• A membrane that allows passage of a given substance is said to be “Permeable”• A membrane that DISallows passage of a given substance is said to be “Impermeable”• The plasma membrane is selectively permeable: permeable to some particles but impermeableto others– Determined by the lipid and protein composition of the plasma membraneWhat properties influence permeability?• Relative solubility of a molecule in lipid– Highly soluble: uncharged (O2 & CO2) and non-polar molecules (fatty acids)– Water-soluble: charged (Na+ & K+) and polar molecules (glucose)• Size of the molecule– Large molecules either enter with difficulty or not at all– Small