CHapter 7 BIology I MY notes
CHapter 7 BIology I MY notes BSC 2010
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This 5 page Class Notes was uploaded by Marla Notetaker on Saturday October 8, 2016. The Class Notes belongs to BSC 2010 at University of South Florida taught by Dr Daniel in Summer 2015. Since its upload, it has received 18 views. For similar materials see Cellular processes in Biology at University of South Florida.
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Date Created: 10/08/16
Chapter 7 – Membrane Structure and Function Yellow: Vocabulary GREE: Key concepts Selective permeability: “allows some substances to cross it more easily than others” Aquaporins: proteins that allow water (polar molecule) to pass through the tails (nonpolar) sections of the phospholipid bilayer of the cell. Concept 7.1 Amphipathic: has a hydrophilic (likes water – polar head) and hydrophobic (does not like water – nonpolar tail) part. Most proteins are also amphipathic; their hydrophobic part within the membrane and the hydrophilic portion beyond the border of the membrane with the hydrophilic part Fluid mosaic model: sketch of how the membrane and its surrounding looks like. I. The Fluidity of Membranes The lipids are much easier to move horizontally than vertically SOMETIMES then may flipflop… the lipid on the top layer switches to the later on the bottom. SOMETIMES proteins shift laterally along the membrane, however they are larger than phospholipids and its harder, plus they are most likely attached to the cytoskeleton of the cell Fluidity of the membrane: o Lower temperatures: Fluid until the phospholipids are TOO close together and they move very slowly (solidification) making the layer viscous – this solidification depends on the “type of lipid it is made of” Much more fluid if the tails (hydrophobic) portions of the phospholipids are UNsaturated (one of the legs is bended) because this “bend” separates them and allows movement o Cholesterol (in animal cells): If temperature is HIGH… slows the movement by sticking in the middle it’s not TOO fluid If temperature is LOW…makes space between the phospholipids, enough for them NOT stop moving “The fluidity of the membrane affects both its permeability and the ability of membrane proteins to move to where their function is needed” II. Membrane protein and their function The proteins within the membrane determine its function Types of proteins: o Integral proteins: Get INTO the hydrophobic portion (tails) Transmembrane: go from SIDE TO SIDE… all the way though Usually they are bonded by α helices o Peripheral proteins: they are “leaning” on the top/bottom of the membrane Don’t directly are In the membrane but interact with the proteins that ARE in the membrane Functions of the membrane proteins: o Transport o Enzymatic activity o Signal transduction: the outside of the enzyme receives a signal and passes it to the inside. o Cellcell recognition: to identify our own cells o Intercellular joining: junctions, hook cells together o Attachment of the cytoskeleton and the extracellular matrix (ECM) Page 128 with HIV topic – absence of CCR5 creates sort of immunity III. The Role of Membrane Carbohydrates in Cellcell recognition Important for “sorting of cells into tissues and organs in an animal embryo. Identify which are our own cells Glycolipids: covalent bonds between short carbohydrates (about 15) and lipids Glycoproteins: covalent bonds between carbohydrates and proteins (most of the membrane carbohydrates) When referring blood (A,B,O,AB) the change is due to “variations in the carbohydrate part of the glycoproteins on the surface of red blood cells” IV. Synthesis and Sidedness of Membranes Membranes have specific orientations ^ this depends on how they are assembled by the ER and GA Concept 7.2 I. The Permeability of the Lipid Bilayer Hydrophobic (nonpolar): Hydrocarbons and others, can cross easily the tails of the bilayer because those are also nonpolar Hydrophilic (polar): the heads of the bilayer does not allow for direct communication between the outside and the inside because they are separated by the nonpolar portion. These polar molecules can pass very slowly or with other type of aid II. Transport Proteins Channel Proteins: Hydrophilic (most likely) proteins that go from one end to the other of the membrane and can carry hydrophilic molecules in and out of the cell (like a tunnel) o Aquaporin: example of channel protein to transport water Carrier Proteins: Takes the molecule inside it and it changes its shape and moves it along, through it (like squeezing toothpaste) Transport proteins are VERY specific in what they transport Concept 7.3 Cells have thermal energy: movement of particles inside the cell Diffusion: when PARTICLES move through the space, eventually to reach dynamic equilibrium Concentration gradient: move from areas of high concentration to low concentrations Passive transport: diffusion should not require energy I. Effects of Osmosis on Water Balance Osmosis: movement of WATER across a semipermeable membrane a. Water Balance of Cells Without Cell Walls Tonicity: ability of the cell to gain or lose water. o Depends on the concentration of the solute and its composition Everything depends on the POINT OF VIEW YOU ADOPT… usually is the solution’s point of view and NOT the cell Type of solutions: o Isotonic: the solution has the same amount of solute concentration as the inside of the cell… water does not move at all o Hypertonic: the solution has MORE solute concentration than the cell… cell will LOSE water o Hypotonic: the solution has LESS solute concentration than the cell… cell will GAIN water Osmoregulation: control of water movement b. Water Balance of Cells Cell Walls Turgor pressure: because the cell wall is not very flexible when the cell swells with too much water the cell wall applies back pressure which does not allow it to take in more water States of plant cell in regards to water volume: o Turgid: the plant cell has the maximum amount of water, which is the best for it o Flaccid: when there is no water coming in or out o Plasmolysis: when the cell does not have enough water and the plasma membrane disjoins the cell wall. II. Facilitated Diffusion: Passive Transport Aided by Proteins Facilitated diffusion: when a protein is used to pass the chemical Move DOWN the concentration gradient Channel proteins: o Ions channels: transport ions Gate channels: “open/close in response to stimuli” Electrical stimuli: Neurons “Specific” channels: only open/close when something specific binds to it (besides the actual chemical needing transportation) o Carrier proteins: the chemical somehow “changes” the shape of the protein until it transports the chemical to the other side Concept 7.4 Particles moves AGAINST the concentration gradient (from low to high) This requires energy… most likely ATP I. The Need for Energy in Active Transport Active transport: requires energy Most of the proteins that do this are CARRIER proteins… because they SELECT what chemicals to send. Know the sodiumpotassium pump… its explained in details and with pictures on p. 135 of the USF version of the Bio I book II. How Ion Pumps Maintain Membrane Potential Membrane potential: the different electrical charge of the cell and its surrounding… the inside of the cell should be more negative (50 200 millivolts (mV)) Movement of ions: o “ Because the inside of the cell is negative compared with the outside, the membrane potential favors the passive transport of cations into the cell and anions out if the cell” (p.135) – Electrical Gradient o Factors for ion diffusion: Type of chemical/concentration of it Electrical charge Electrogenic Pump: “transport protein that generates voltage across the membrane o Sodium – potassium pump: so far the strongest electrogenic pump in animal cells o Proton pump: so far the strongest electrogenic pump in plants, fungi, and + Bacteria – moves H out of the cells – ATP synthesis III. Cotransport When a protein take one chemical into the cell and another out at the same time Concept 7.5 When particles are way too big to be moves through the regular proteins vesicles are created to transport this “bulk’ I. Exocytosis Movement of this “bulk” OUTSIDE the cell II. Endocytosis Movement of this “bulk” INSIDE the cell Steps: o The plasma membrane makes a small pocket inward and stretches out o When it stretches it surrounds what is needed to bring inside and it pinches, closing up the space and forming a vesicle o Pulls vesicle inside Types of Endocytosis o Phagocytosis: membrane stretches OUT and surrounds the “food” which a lysosome will digest later. o Pinocytosis: invagination (dip IN) of the membrane creating a coated vesicle and fuse with lysosome o Receptor – Mediated Endocytosis: kind of like pinocytosis but this one has receptors inside and the chemicals (Ligands) bind to this receptors.
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