Week 2 Notes
Week 2 Notes EXSC 223
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This 11 page Class Notes was uploaded by Madison Waterman on Sunday September 4, 2016. The Class Notes belongs to EXSC 223 at University of South Carolina taught by Dr. Raymond Thompson in Fall 2016. Since its upload, it has received 105 views. For similar materials see Anatomy and Physiology I in Science at University of South Carolina.
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Date Created: 09/04/16
EXSC 223: Week of 8/29/16 Notes from the textbook Ch. 3.3-3.5 3.3 Passive membrane transport is diffusion of molecules down a concentration gradient • Passive transport o Diffusion § Tendency of molecules or ions to move from an area where they are in high concentration to an area where they are in low concentration § Move down/along the concentration gradient § Random motions • Powered by intrinsic kinetic energy • Collisions cause particles to go in random directions o Particles scatter and disperse § Speed of diffusion is affected by: • Molecule size (smaller molecules=faster diffusion rate) • Temperature (warmer system=faster diffusion rate) § In a closed container, a uniform mixture will be the result § At equilibrium • Molecules move equally in all directions • No net movement o Filtration • Plasma membrane o Selectively permeable § Lets nutrients in § Keeps bad substances out § Keeps valuable proteins in § Lets waste out o Unhealthy cells have a damaged plasma membrane o Molecules or ions can diffuse in if: § Lipid soluble § Small enough to pass through membrane channels § Assisted by a carrier molecule • Simple diffusion: unassisted diffusion of lipid soluble or very small molecules • Facilitated diffusion: assisted diffusion o Molecule binds to proton carriers in the plasma membrane and ferried across § Transmembrane integral proteins transport polar molecules or molecules too large (ex: sugars and amino acids) o OR molecules move through water filled protein channels § Transmembrane proteins (integral proteins) usually transport ions or water • Leakage channels: always open (ions or water move according to concentration gradient) • Gated channels: opened or closed by chemical or electrical signals • Osmosis: diffusion of a solvent (usually water) through a membrane o water can diffuse through water-specific channels called aquaporins (AQPs) o occurs when water concentration differs on the two sides of the membrane o osmolarity: total concentration of all solute in a solution • Tonicity: ability of a solution to change shape of cells by altering the cells’ internal water volume o Isotonic: same solute/water concentration inside and outside of the cell § Cells retain normal size and shape § Water moves in and out of the cell at an equal rate o Hypertonic: solution has a higher concentration of solute than in the cell § Cell shrinks § water leaves the cell o Hypotonic: solution is dilute, has a lower concentration of solute than in the cell § Cell becomes bloated and lyse (bursts) § Cell takes in water 3.4 Active membrane transport directly or indirectly uses ATP • Active transport o Energy required o Moves molecules against their gradient o Ex: sodium-potassium pump § 2 K+ in § 3 Na+ out • Vesicular transport by endocytosis o Phagocytosis: ingesting of solid material o Pinocytosis: ingesting of fluid material o Steps: § Protein-coated (usually clathrin) pit forms in the plasma membrane and ingests a substance § Pit pinches off and the substance is now in this protein-coated vesicle inside the cell § The protein coat falls off and goes to the plasma membrane to be recycled (leaving the vesicle uncoated) § Uncoated vesicle fuses with a sorting vesicle (endosome) § The fused vesicle may: • Fuse with a lysosome • OR deliver contents to the plasma membrane on the opposite side of the cell (transcytosis: move substances into the cell, across, and eventually out) 3.5 Selective diffusion establishes the membrane potential • Membrane potential= voltage across the membrane o Voltage=electrical potential energy resulting from separation of oppositely charged particles • Resting membrane potential: -50 to -100 millivolts (mV) o Polarized o Inside cell=negative o Determined by K+ concentration o Active transport of K+ and Na+ maintains gradient (sodium-potassium pump) Lecture Notes on 8/29 Lipid Rafts • Specialized area of plasma membrane • Important to localize proteins to certain areas or move receptors • Contain higher concentrations of cholesterol and sphingolipids (saturated fatty acids) to maintain a more rigid structure Transport and digestion • Plasma membrane is selectively permeable • Passive transport o Simple diffusion o Facilitated diffusion o Osmosis • Active transport o Primary active transport o Secondary active transport • Vesicular transport o Endocytosis o Exocytosis o Osmosis Diffusion • Movement from high to low concentration • Passive process (does not require energy) • Ex: dropping a tablet in a beaker of water and the contents spread throughout the beaker until there is a uniform substance • Rate of diffusion affected by: o Gradient: big contrast in gradient=faster diffusion rate o Temperature: high temperature=faster diffusion rate o Particle size: smaller particles=faster diffusion rate • Hydrophobic membrane prevents diffusion except if o Lipid soluble o Small size o Assisted by carrier molecule • Simple diffusion: lipid soluble (fatty acids, steroids), small, uncharged molecules • Facilitated diffusion: still a passive process because the substances move with their concentration gradients but they need help crossing the membrane because they are large, charged, or lipid insoluble o Channel proteins: ex/ depolarization (transport Na+ and K+) o Carrier proteins: lipid insoluble solutes (glucose, amino acids) o Substances move through according to concentration gradient o Carriers can become saturated • Osmosis o Diffusion of water across a semi-permeable membrane o Water moves through aquaporins o Occurs when concentration of water is different on opposite sides of the membrane o Increased concentration of a solute will decrease the concentration of water (due to displacement) o Osmolarity: total concentration of solute particles in solution o When 2 solutions differ in osmolarity, water will move along a concentration gradient to reach equilibrium o When hydrostatic pressure of water=osmotic pressure, there is no more net movement by osmosis • Osmosis vs diffusion o Diffusion is movement of solute from high to low concentration o Osmosis is the movement of water from low to high solute concentration when separated by a semipermeable membrane Effects of varying solute concentration • Tonicity: ability of a solution to change the shape of a cell by altering its internal solvent (water) volume • Isotonic: solutions with same solute concentration as the cytosol o Cell stays the same o Water diffuses in and out of the cell at equal rates • Hypertonic: solution with greater solute concentration than cytosol o Water diffuses out of the cell (to dilute the higher solute concentration that is outside the cell) o Cell shrivels • Hypotonic: solution with a lower solute concentration than the cytosol o Water diffuses into the cell (to dilute the higher solute concentration that exists inside the cell) o Cell swells and lyses (breaks) Active Transport • Active processes: metabolic energy required from the cell • Energy is necessary for pumping substances up (against) a concentration gradient o Primary: directly uses energy o Secondary: indirectly uses energy • PRIMARY active transport example: Sodium-Potassium Pump (SPP) (fig. 3.10) o 3 Na+ attach to the SPP § causes phosphorylation by ATP o phosphorylation causes protein to change shape o shape change causes Na+ to be released outside of the cell o 2 K+ ions attach o K+ binding triggers the release of the phosphate group that was added in step 1 o Loss of the phosphate restores original shape of the pump protein • SECONDARY active transport example o Na+-glucose symport transporter loading glucose from the extracellular fluid o As Na+ diffuses back across membrane through a membrane cotransport protein, it drives glucose against its concentration gradient into the cell • Secondary active transport takes advantage of the gradient created by the primary active transport • Vesicular transport o transportation of large particles and macromolecules across the cellular membrane inside membranous fluid sacs o types: § endocytosis: moves substances from outside the cell into the cell in a vesicle § transcytosis: moves substances through the cell and out the other side through a vesicle § exocytosis: moves a substance out of a cell through a vesicle Notes from the textbook Ch. 3.6 &3.7 3.6 Cell adhesion molecules and membrane receptors allow the cell to interact with its environment • Cell interaction o Directly with other cells o Indirectly: responds to extracellular chemicals § Hormones § Neurotransmitters § Etc. o Glycocalyx used in both § Cell adhesion molecules (CAMs) § Plasma membrane receptors • CAMs o Thousands on every cell o Play key roles in embryonic development, wound repair, immunity o Jobs: § It is the “Velcro” cells use to anchor themselves to molecules in the extracellular space and each other § “arms” that migrating cells use to pull themselves past one another § SOS signals to white blood cells to go to an infected/injured area § Mechanical sensors to respond to changes in tension and fluidity at the cell surface § Transmit intracellular signals that direct cell migration, proliferation, and specialization • Roles of plasma membrane receptors o Integral proteins and glycoproteins serve as binding sites o Contact signaling § Cells touch and recognize one another § Important for notmal development and immunity o Chemical signaling § Ligands: chemicals that bind to plasma membrane receptors • Most neurotransmitters • Hormones • Paracrines § Different cells respond differently to the same ligand • Ex: Acetylcholine stimulates skeletal muscle cells but it inhibits heart muscle § Steps • Ligand binds to receptor • Receptor’s structure changes • Cell proteins are altered § G-protein linked receptors: exert effect indirectly through a G-protein • Signals one or more intracellular chemical signals (second messengers) • Carries out message inside the cell 3.7 Cytoplasmic organelles each perform a specialized task • Cytoplasm has 3 parts o Cytosol: semitransparent fluid that holds cytoplasmic elements o Inclusions: chemical substances that may or may not be present depending on the cell § Ex/ melanin in skin cells and lipid droplets in fat cells o Organelles: metabolic machinery of the cell • Organelles o “little organs” o most are membrane bound to help organize the cell § ribosomes and centrioles do not have membranes • mitochondria o power plants of cell o provide most of the cell’s ATP o the higher the cell’s energy requirement, the more mitochondria are present § ex: the kidney and liver have a lot of mitochondria o double membrane § outer: smooth and featureless § inner: folds (cristae) o matrix= gel-like substance o generates ATP by aerobic cellular respiration o has own DNA, RNA, and ribosomes o may have descended from bacteria • Ribosomes o Small o Made of proteins and rRNA o Site of protein synthesis o Made of 2 globular subunits o Free ribosomes: float freely in cytosol § Make soluble proteins o Membrane bound ribosomes: attached to ER (rough ER) § Synthesize proteins for incorporation in cell membrane or lysosomes or export from the cell o Can switch between free and membrane bound • Endoplasmic reticulum (ER) o Extensive system of interconnected tubes and parallel membranes enclosing fluid filled cavities (cisterns) o Continuous with outer nuclear membrane o Rough ER § Studded with ribosomes § Ribosomes here manufacture all proteins secreted from cell § Integral proteins and phospholipids for cell membrane manufactured here o Smooth ER § Continuous with rough ER § No ribosomes attached to it § Enzymes integrated in its membrane catalyze reactions involved with these tasks: • Metabolize lipids • Synthesize cholesterol and phospholipids • Synthesize steroid based hormones • Absorb, synthesize, and transport fats • Detoxify drugs • Break down stored glycogen § Skeletal and cardiac muscle cells have elaborate smooth ER (sarcoplasmic reticulum) • Golgi Apparatus o Stacked and flattened membranous sacs o “traffic director” for cell proteins o modify, concentrate, and package proteins and lipids made at the rough ER § transport vesicle from rough ER fuses with the cis face (receiving side) if tge Golgi § proteins are modified • sugar groups added • sugar groups removed • sometimes phosphates are added § proteins tagged for delivery for specific location in 3 types of vesicles and leave from the trans face (shipping side) • 1: secretory vesicles: export from plasma membrane (exocytosis) • 2: vesicles with lipids and transmembrane proteins go to plasma membrane or a membranous organelle • 3: vesicle with digestive enzymes are packaged into lysosomes and stay in the cell • Peroxisomes o Sacs with enzymes in it: oxidases and catalases o Oxidases § Use oxygen to detoxify harmful substances (ex: alcohol, formaldehyde) § Neutralize free radicals (convert to hydrogen peroxide) § But hydrogen peroxide is also dangerous § So catalase converts it to water § Free radicals and hydrogen peroxide are normal byproducts of cellular metabolism o Numerous in liver and kidney (important organs for detoxification) • Lysosomes o Start as endosomes with inactive enzymes inside o Spherical membranous organelles with activated digestive enzymes o Large and abundant in phagocytes o Work best in acidic conditions o Membrane has H+ (proton) pumps to maintain acidic pH o Place where digestion can happen safely in the cell • Endomembrane system o Work together to produce, degrade, store, and export biological molecules and degrade potentially harmful substances o Made of the following organelles: ER, golgi apparatus, secretory vesicles, lysosomes, and nuclear membrane • Cytoskeleton o Microfilaments o Intermediate filaments o Microtubules o Centrosome o Centrioles Lecture Notes on 8/31 Vesicular transport • Starts with endocytosis • Plasma membrane pinches off into a small pit coated with protein(clathrin) • Ingests substance • Protein coated vesicle detaches and goes into the cell • Protein coat detaches and is recycled to the plasma membrane • Uncoated vesicle fuses with an endosome (sorting vesicle) o Helps direct substance to where it needs to go • Transport vesicle (membrane components) goes to the plasma membrane for recycling • Fused vesicle may: o Fuse with a lysosome for the digestion of its contents o Deliver its contents to the plasma membrane on the opposite side of the cell (transcytosis) 3 types of endocytosis • Phagocytosis: cell eating o Engulf material into the cell o Pseudopods: cytoplasmic extensions that wrap around the particle o Form phagosome (type of vesicle) o Ex/ common function of macrophages • Pinocytosis: cell drinking o Cell gulps drops of extracellular fluid containing solutes o No receptors are used so the process is non-specific o Most vesicles are protein coated o Routine activity of most cells for extracellular fluid sampling • Receptor mediated endocytosis o Extracellular substances bind: § Specific receptor proteins § The cell ingests § Concentrates substance in protein coated vesicles § Selective endocytosis o Ligands (molecules that bind to receptors) may be: § Released inside the cell § OR combined with a lysosome to digest its contents o Receptors are recycled to the plasma membrane in vesicles Exocytosis • Substances released from the cell (hormones, neurotransmitters, waste, etc.) • Steps: o Membrane bound vesicle migrates to the plasma membrane § Vesicle SNARE (v-SNARE) protein inside the vesicle o V-SNAREs bind with the t-SNARES (plasma membrane proteins, t=target) § Process is called docking § Proteins twist together to hold the vesicle at the plasma membrane o Vesicle and plasma membrane fuse and a pore opens up o Vesicle contents are released to the cell’s exterior Summary of transport and digestion • Cells segregate interior and exterior environments with the plasma membrane that regulates transportation • Cells permit selected substances to cross the plasma membrane and through the cytosol via passive or active mechanisms o Diffusion and osmosis o Active transport (primary and secondary) o Vesicle transport (endocytosis, transcytosis, exocytosis) Identification of alien invaders • Cell to cell recognition • Glycoproteins serve as identification tags that are specifically recognized by other cells o Ex/ in organ transplants you have to wait for a match to your glycocalyx (glycoprotein) so that your body accepts it rather than identifying it as an alien invader and attacking the new organ Skeletal systems of cells • Provides supporting cell structure • Provides machinery to generate cell movement • 3 types of structural rods o actin subunit: microfilament o fibrous subunit: intermediate filament o microtubule • microfilaments o strands made of spherical protein units o called actins o attached to cytoplasm side of the plasma membrane o supports cell surface and resists compression o microvilli: cell membrane projections composed of microfilaments § increase surface areas § increase absorption • intermediate filaments o tough, insoluble protein fibers constructed like woven ropes o high tensile strength o internal stabilizer can resist pulling forces o does not bind ATP o made of keratin and vimentin • microtubules o hollow tubes of spherical protein sub units called tubulins o extend from the centrosome o composed of tubulin o dynamic o determines the cell’s shape and organelle distribution o associates with motor proteins • centrioles o small barrel shaped organelles located in the centrosome near the nucleus o pinwheel arrangement of 9 triplets of microtubules o organize mitotic spindles during mitosis o form the bases of cilia and flagella 9/2 Class cancelled
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