Chapter 3 Cells The Living Units I Overview of the Cellular Basis of Life pp 65 66 A The four concepts of the cell theory state p 65 1 Cells are the basic structural and functional units of life 2 The activity of an organism depends on the activities of its cells 3 The biochemical activities of a cell are dictated by their organelles 4 The continuity of life has a cellular basis B Characteristics of Cells pp 65 66 Figs 3 1 3 2 1 Cells vary greatly in their size shape and function 2 All cells are composed primarily of carbon hydrogen nitrogen and oxygen 3 All cells have the same basic parts and some common functions 4 A generalized human cell contains the plasma membrane the cytoplasm and the nucleus II The Plasma Membrane Structure pp 67 69 A The Fluid Mosaic Model pp 67 68 Figs 3 3 3 4 1 The plasma membrane is composed of a double layer of phospholipids embedded with small amounts of cholesterol and proteins 2 The phospolipid bilayer is composed of two layers of phospholipids lying tail to tail with their polar heads exposed to water inside and outside the cell 3 The inward facing and outward facing surfaces of the plasma membrane differ in the kinds and amounts of lipids they contain a Glycolipids are found only in the outer membrane b Lipid rafts are also found only in the outer membrane and are assumed to function in cell signaling 4 Integral proteins are firmly inserted into the plasma membrane a Most integral proteins are transmembrane proteins that span the entire width of the membrane and are involved with transport as channels or carriers 5 Peripheral proteins are not embedded in the plasma membrane but attach to integral proteins or to phospolipids a Peripheral proteins may function as enzymes or in mechanical functions of the cell 6 The glycocalyx is the fuzzy sticky carbohydrate rich area surrounding the cell B Specializations of the Plasma Membrane p 69 Fig 3 5 1 Microvilli are fingerlike extensions of the plasma membrane that increase the surface area of the cell 2 Most body cells are bound together using glycolipids specialized interlocking regions or specialized membrane junctions a Tight junctions are a type of membrane junction in which integral proteins on adjacent cells fuse together to form an impermeable junction in order to prevent molecules from passing through the extracellular space between cells b Desmosomes are mechanical couplings that are scattered along the sides of adjoining cells that prevent their separation and reduce the chance of tearing when a tissue is stressed c Gap junctions are a communication junction between cells that allows substances to pass between adjacent cells III The Plasma Membrane Functions pp 70 83 A Membrane Transport pp 69 81 Tables 3 1 3 2 Figs 3 6 3 14 1 The plasma membrane is a selectively permeable barrier regulating how substances pass into and out of the cell 2 Passive processes do not use energy and move substances down a concentration gradient a Diffusion is a process in which substances move directly through the plasma membrane from an area of higher concentration to an area of lower concentration b In facilitated diffusion substances are moved through the plasma membrane by binding to protein carriers in the membrane or by moving through channels c Osmosis is the diffusion of water through a selectively permeable membrane d Filtration is a pressure driven process that forces water and solutes through a membrane or capillary wall 3 Active processes use energy ATP to move substances across a membrane a Active transport uses solute pumps to move substances against a concentration gradient The two kinds of active transport are primary active transport and secondary active transport b Vesicular transport is the means by which large particles macromolecules and fluids are transported across the plasma membrane or within the cell i Exocytosis is a process used to move substances from inside the cell to the extracellular environment c Endocytosis transcytosis and vesicular traffiking are vesicular transport processes that move molecules using protein coated vesicles d Clathrin coated vesicles are the main route for endocytosis and transcytosis of bulk solids e Non clathrin coated vesicles or caveolae are inpocketings of the cell membrane that capture specific molecules in vesicles lined with caveolin not clathrin B Generating and Maintaining a Resting Membrane Potential pp 81 83 Fig 3 15 1 A membrane potential is a voltage across the cell membrane that occurs due to a separation of oppositely charged particles ions 2 The resting membrane potential is a condition in which the inside of the cell membrane is negatively charged compared to the outside and ranges in voltage from 25 to 2100 millivolts a The resting membrane potential is determined mainly by the concentration gradient of potassium K1 b Active transport pumps ensure that passive ion movement does not lead to an electrochemical equilibrium across the membrane thus maintaining the resting membrane potential C Cell Environmental Interactions pp 83 84 1 Cells can interact directly with other cells respond to extracellular chemicals and interact with molecules that direct migration 2 Roles of Cell Adhesion Molecules a Cell adhesion molecules CAMs are glycoproteins that play roles in embryonic development wound repair and immunity 3 Roles of Membrane Receptors Fig 3 16 a Membrane receptors are integral proteins and glycoproteins that serve as binding sites b Some membrane receptors function in contact signaling electrical signaling and chemical signaling 4 Nitric oxide consisting of one atom of oxygen and one atom of nitrogen is the first known gas to act as a biological messenger IV The Cytoplasm pp 84 95 A The cytoplasm is the cellular material between the cell membrane and the nucleus and is the site of most cellular activity p 84 1 There are three major elements of the cytoplasm cytosol cytoplasmic organelles and cytoplasmic inclusions B Cytoplasmic Organelles pp 84 95 Table 3 3 Figs 3 17 3 27 1 Mitochondria are sausage shaped membranous organelles that are the power plants of the cell producing most of its ATP 2 Ribosomes are small staining granules consisting of protein and ribosomal RNA that are the site of protein synthesis 3 The endoplasmic reticulum is an extensive system of tubes and membranes enclosing fluid filled cavities called cisternae that extend throughout the cytosol a The rough endoplasmic reticulum has ribosomes that manufacture all proteins