KIN 2500 Cells Supplemental Instruction A Generalized Cell ANSWER KEY SI Matthew Landry mland84 lsu edu The plasma membrane forms the cell s flexible outer surface it separates the external and internal environments The purpose of the plasma membrane is to o Create a selective barrier that regulates flow of material in and out of the cell o Play a key role in communication among cells The cytoplasm is all of the cellular contents between the plasma membrane and the nucleus It is comprised of two compartments o Cytosol the fluid portion of the cytoplasm containing water dissolved solutes and suspended particles o Organelles specialized structures within the cell that have characteristic shapes and perform specific functions in cellular growth maintenance and reproduction The nucleus is a large organelle that houses most of the cell s DNA Within the nucleus each chromosome a single molecule of DNA associated with several proteins contains thousands of hereditary units called genes that control most aspects of cellular structure and function The Plasma Membrane The plasma membrane is a flexible yet sturdy barrier that surrounds and contains the cytoplasm of a cell o Its structure is described as the fluid mosaic model o Which means the molecular arrangement of the plasma membrane resembles a continually moving sea of lipids that contains a mosaic of many different proteins o Plasma membranes are not completely permeable to any substance This property is called selective permeability The basic structural framework of the plasma membrane is the lipid bilayer which is two back to back layers made up of three types of lipid molecules o Phospholipids o Cholesterol o Glycolipids o Integral Proteins Membrane proteins are divided into two categories Definition Extend into or through the lipid bilayer and are firmly embedded in it KIN 2500 Cells Supplemental Instruction ANSWER KEY SI Matthew Landry mland84 lsu edu Most are transmembrane proteins which means that they span the entire lipid bilayer and protrude into both cytosol and extracellular fluid o Peripheral Proteins Definition Not as firmly embedded in the membrane and are attached to membrane lipids or integral proteins at the inner or outer surface of the membrane Most are glycoproteins proteins which means that they are proteins with carbohydrate groups attached to the ends that protrude into the extracellular fluid Functions of Membrane Proteins Ion Channels pores or holes through which specific ions such as potassium ions K can flow through to gain entry or leave the cell Carriers or Transporters selectively moving a polar substance or ion from one side of the membrane to the other Receptors serve as special recognition sites Each type of receptor recognizes and binds a specific type of molecule Ex insulin receptors bind the hormone insulin Ligand a special molecule that binds to a receptor Enzymes catalyze specific chemical reactions at the inside or outside surfaces of cells Cell identity markers enable a cell to recognize other cells of the same kind or respond and recognize to potentially dangers foreign cells Transport across the Plasma Membrane Fluid within cells is called intracellular fluid ICF while fluid outside body cells is called extracelluar ECF ECF is found in three places o Between the cells of tissues Interstitial o In blood vessels plasma o In lymphatic vessels lymph Substances generally move across cellular membranes via transport processes that are passive or active depending on whether they require cellular energy o In passive processes a substance moves down its concentration gradient or electrical gradient to cross the membrane using its own kinetic energy KIN 2500 Cells Supplemental Instruction ANSWER KEY SI Matthew Landry mland84 lsu edu o In active processes cellular energy is used to drive a substance uphill against its concentration or electrical gradient The cellular energy used is usually in the form of adenosine triphosphate ATP Materials may cross plasma membranes using kinetic energy transporter proteins or vesicles Transport across the Plasma Membrane Transport by Transporter Proteins Kinetic Energy Transport Transport in Vesicles Diffusion Osmosis Facilitated Diffusion Active Transport Endocytosis Exocytosis What is diffusion a passive process in which the net movement of substances is from a region of higher concentration to a region of lower concentration o An example of diffusion in the body is When we inhale Within the lungs the oxygen moves from its site of high concentration in the air sacs to the low concentration in the blood cells The passive process in which the net movement of water molecules through a selectively permeable membrane from an area of higher water concentration low solutes to low water concentration high solutes is osmosis A passive process accomplished with the assistance of transmembrane proteins functioning as carriers is facilitated diffusion A primary example of this is the movement of glucose the body s preferred energy source for ATP synthesis Transport across the Plasma Membrane Kinetic Energy Transport Diffusion Osmosis Transport by Transporter Proteins Facilitated Diffusion Active Transport Transport in Vesicles Endocytosis Exocytosis ANSWER KEY KIN 2500 Cells Supplemental Instruction What is active transport The process by which substance are SI Matthew Landry mland84 lsu edu transported across the plasma membrane with the expenditure of energy by the cell typically high to low concentrations o Explain the process The substance makes contact with a specific site on a transporter protein ATP splits and the energy from the split causes a chance in the protein that expels the substance on the opposite side of the membrane o This process is vital in maintaining ion concentrations in body cells and extracellular fluids Endocytosis is the movement of substance into a cell in vesicles There are three types o Receptor mediated endocytosis ligand receptor complexes trigger infolding of a clathrin coated pit that forms a vesicle containing ligands o Phagocytosis Cell eating movement of a solid particle into a cell after pseudopods engulf it to form a phagosome o Bulk phase endocytosis Cell drinking movement of extracellular fluid into a cell by infolding of plasma membrane to form a vesicle Exocytosis is the movement of substances out of a cell in secretory vesicles that fuse with the plasma membrane and release their contents into the extracellular fluid Transcytosis