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Lecture 2- Cellular Bio I.docx

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BIO 141

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Lecture 2: Cellular Biology I I. Cell Theory Concepts: 1. Cells are the functional and structural units of living organisms 2. The activity of an organism is dependent on both the individual and collective activity of the cells that comprise that organism 3. Subcellular structures determine the biochemical activities of cells (i.e., principle of complementarity) 4. Continuity of life has a cellular basis II. Generalized Cell A. Major parts 1. Nucleus 2. Cytoplasm a. Contain organelles (see below) 3. Plasma membrane III. Plasma Membrane A. Fluid mosaic model 1. Membranes are a mosaic of different proteins are embedded in a phospholipid bilayer 2. Hydrophilic portions of both proteins and phospholipids are maximally exposed to water 3. Hydrophobic portions are in the nonaqueous environment inside the membrane B. Types of proteins: 1. Integral: transmembrane proteins; span the hydrophobic interior a. Channels b. Carriers 2. Peripheral: not embedded; attached to surface a. Enzymatic activity b. Structure C. Carbohydrates associated with the exterior surface of the membrane 1. Glycolipids 2. Glycocalyx: attached to proteins in contact with extracellular matrix D. Function of membrane proteins: 1. Transport 2. Enzyme 3. Receptor sites 4. Intercellular junctions 5. Cell-cell recognition 6. Cytoskeletal and extracellular matrix attachment E. Specialized Structures and Functions 1. Microvilli: increase surface area; absorption 2. Membrane junctions a. Tight junctions—impermeable junctions b. Desmosomes—anchoring junctions; plaques and linkers; intermediate filaments c. Gap junctions—movement of chemicals between adjacent cells; connexons F. Membrane transport 1. Membranes are selectively permeable 2. Movement across membranes a. Passive and active processes 3. Passive movement: Diffusion a. Net movement of a substance down a concentration gradient i. Concentration gradient—graded concentration change over a distance in a particular direction b. Results from intrinsic kinetic energy i. Affected by temperature and molecular size c. Random molecular movement d. Continues until a dynamic equilibrium is reached 4. Types of diffusion a. Simple—nonpolar substances that are lipid soluble pass directly through lipid bilayer i. Polar and charged particles can diffuse if they can fit through pores b. Osmosis—diffusion of a solvent through a selectively permeable membrane i. Hypertonic solution—solution with a greater solute concentration than inside a cell ii. Hypotonic solution—solution with a lower solute concentration than inside a cell iii. Isotinic solution iv. Osmolarity—total concentration of all solutes in a solution v. Osmotic pressure—amount of pressure required to prevent net movement of water into a solution c. Facilitated diffusion—lipid insoluble molecules too large to diffuse through membrane pores can move passively with carrier molecules i. Selective—not just size and lipid solubility (specific) ii. Limited by number of carrier molecules present (saturated) 5. Passive movement: Filtration—water and solutes are forced through a membrane or capillary by hydrostatic pressure a. Pressure gradient pushes solute-containing fluid out 6. Active Processes: Active Transport a. Cell uses energy to move substances across the membrane b. Transport molecules harvest energy from ATP to pump molecules against concentration gradients c. Coupled systems—move more than one substance i. Symport—same direction ii. Antiport—opposite direction d. Sodium-Potassium Pump i. Na+ binding (cytoplasm) stimulates ATP formation ii. Phosphorylation causes conformational change iii. Shape change releases Na+ to outside iv. K+ binding causes phosphate release v. Pump returns to original conformation vi. K+ is released to inside 7. Bulk Transport (Active) a. Exocytosis—substance is released from vesicle (membranous sac) i. Fuses with membrane and releases contents to outside b. Endocytosis—large substances progressively enclosed by membrane and taken into cell i. Phagocytosis ii. Pinocytosis iii. Receptor-mediated endocytosis a. Coated pit b. Clathrin IV. Cell-Environment Interactions A. Cell-adhesion molecules (CAMS) 1. Anchor cell to extr
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