Bio 1 Exam 2 Study Guide Chapters 7 11 Chapter 7 Membrane Structure and Function Plasma membrane Membrane proteins A fluid structure embedded with various proteins and lipids The most abundant lipids in the membrane are phospholipids amphipathic molecule with nonpolar tails and polar head regions The structure of the membrane is a phospholipid bilayer which allows lipids and some proteins to drift laterally throughout Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids Membrane fluidity is also affected by the steroid cholesterol at different temperatures At warm temperatures cholesterol restricts the movement of phospholipids within the membrane Peripheral proteins surface bound Integral proteins within the hydrophobic center of the phospholipid bilayer called transmembrane proteins made up of nonpolar amino acid regions Transport proteins allow the passage of certain hydrophilic substances across the membrane aquaporins facilitate water movement through the membrane Other transport proteins carrier proteins change shape to shuttle them across the membrane 6 major functions of membrane proteins transport enzymatic activity signal transduction cell cell recognition intercellular joining attachments to cytoskeleton and extracellular matrix Membrane carbohydrates and cell cell recognition Cells recognize each other by binding to carbohydrates on the extracellular surface of the plasma membrane Permeability of the Lipid Bilayer Polar molecules can t easily cross the plasma membrane nonpolar molecules such as hydrocarbons can readily dissolve into the lipid bilayer Passive transport across the membrane Diffusion random movement of molecules which spread out evenly into available space no energy is required Molecules move equally in one direction as in the other Passive transport diffusion of a substance across a biological membrane Concentration gradient region where the density of a substance increases or decreases No work is done to move across the gradient Osmosis diffusion of water across a selectively permeable membrane water moves from an area of high concentration to low concentration until the solute concentration equilibrates Water balance of cells without cell walls Tonicity a solution causes a cell to gain or lose water Isotonic solution concentration of the solute is the same inside the cell as it is outside There is no net water movement Hypertonic solution solute concentration is greater outside the cell than inside and the cell loses water Hypotonic solution solute concentration is lower outside the cell than inside the cell gains water Osmoregulation control of solute concentration and water balance Water balance of cells with walls Cell walls help maintain water balance within plant cells Turgid cell cell in a hypotonic solution swells until the wall opposes uptake Flaccid cell cell and its surroundings are isotonic there is no net movement of water into the cell plant may wilt Plasmolysis usually a lethal effect plant cells lose water in a hypertonic environment and eventually the membrane pulls away from the wall Facilitated diffusion Transport proteins speed the movement of molecules across the plasma membrane This passive movement is aided by channel proteins Ion channels that open or close in response to a stimulus gated channels Active transport Membrane potential Solutes are moved against their concentration gradients via embedded protein membranes Energy is required in the form of ATP One type of active transport is the sodium potassium pump The voltage difference across a membrane This is created by differences in the distribution of positive and negative ions across a membrane Electrochemical gradient drives the diffusion of ions across a membrane It is made up of both the ion s concentration gradient and the effect of the membrane potential on the ion s movement Electrogenic pump a transport protein that generates voltage across a membrane It helps store energy that can be used for cellular work o Sodium potassium pump major pump of animal cells o Proton pump main pump in plants fungi and bacteria Cotransport occurs when active transport of a solute indirectly drives transport of other solutes Bulk transport Large molecules must cross the plasma membrane via vesicles energy is required to transport these molecules Exocytosis vesicles transporting large molecules migrate across the plasma membrane and then fuse to it The vesicles are then exposed to the outside surface of the plasma membrane where they then open and release their contents Secretory cells use this process to export their products Endocytosis the cell takes in macromolecules by forming vesicles from the plasma membrane Is the opposite process of exocytosis o 3 types of endocytosis Phagocytosis a cell engulfs a particle in a vacuole which is then digested by fusion with lysosomes Pinocytosis molecules are taken up when extracellular fluid is engulfed into tiny vesicles Receptor mediated endocytosis binding of ligands to receptors triggers vesicle formation Chapter 8 Introduction to Metabolism Metabolism all the chemical reactions that are occurring within an organism is the interaction between molecules within the cell Metabolic pathway starts with a molecule and ends with a different product Catabolic pathways complex molecules are broken down into smaller ones is catalyzed via enymes releasing energy into the system Example of catabolism breakdown of glucose in the presence of Anabolic pathways combine simple molecules to create larger ones energy oxygen is consumed Types of energy Thermodynamics Ex many amino acids come together to synthesis a protein Kinetic motion Heat thermal random movement of atoms Potential energy matter possesses due to structure location Chemical potential energy available for release in chemical reaction Organisms are open systems that can transfer energy and matter between its system and its surroundings Energy can not be created or destroyed but rather transforms into another type of energy such as heat Entropy disorder of the universe spontaneous processes occur without energy input and must increase the entropy of the universe IF entropy decreases in an organism the universes total energy must increase in order to maintain the energy balance In order to know if a reaction occurred spontaneously you must determine energy changes that occurred in the chemical reactions Free energy energy that can do work when
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