Cellular LevelWednesday, September 12, 201212:19 PMCells - the basic structural & functional units of all organisms-Plasma Membrane - Outer boundary, - (2 layers of phospholipids)-Membrane proteins-Cholesterol-Glycoproteins/Glycolipids-Cytoplasm - interior of the cell, contains organelles-Nucleus - contains genes, controls cell activity -Structural Level - Cellular LevelCells are the structural units of all organisms --> reactions occurring inside cells sustain the organismIn a multicellular organism (humans) reactions occurring inside each cell contribute to the organism being sustained (alive)Law of Complementarity - the shape (structure) of a cell dictates the functionFunction of a cell also depends on the type of subcellular structures present (theme of compartmentalization at the cellular level) 3 Parts to Cell -->-PLASMA MEMBRANE- Fluid Mosaic Model --> fluid b/c of presence of unsaturated fatty acids in the phospholipid tails (in the core of the plasma membrane)-Plasma Proteins (membrane proteins) - move constantly due to the plasma membrane in flux forming a "mosaic" (kaleidoscope)-Cholesterol embedded in the tails of the phospholipid forming the plasma membrane, stabilizes the unsaturated fatty acid ("tails") making the plasma membrane less fluid --> referred to us as maintaining the integrity of the plasma membrane Membrane Proteins-Integral proteins - surface of plasma membrane-Peripheral proteins - attached to integral proteins (heads) on cytoplasmic face of plasma membraneFunctions: Transport, Enzymatic activity, receptors, intercellular joining, cell-cell recognition, attachmentto the cytoskeleton-Membrane proteins -Integral proteins - exposed on both sides of the plasma membrane (Transmembrane)-Peripheral proteins-Functions of membrane proteins-Carrier (transport) protein - exhibit specificity, carrier-mediated transport exhibit saturation-Facilitated diffusion-Active transportMembrane proteins may act as membrane-bound enzymes (adenylate-cyclase)Intercellular joining --> transmembrane proteins form junctions b/t adjacent cells-Function of membrane proteins:-Cell to cell recognition --> acting as signal molecules-Carbohydrates attached to the plasma membrane proteins is termed: Glycoprotein --> On the surface of the cell to act as a signal molecule-On the external surface of the plasma membrane - a glycoprotein-rich and a glycolipid-rich are called the: Glycocalyx - Glycolipid and carbohydrate attached to the plasma membrane, acts as the ultimate molecular marker of a cell (ex. Sperm approaching ovum by expression of glycocalyx on the surface of the ovum), regulates cell migration during developmental stages in the human body-The pattern of carbohydrate in the glycocalyx is specific for each type of cell, changes in this pattern indicate cancer-Cytoskeleton (cell's skeleton) - Attached to the membrane proteins to maintain the shape ofthe cell and to allow movement within the cell.Membrane Junctions:-Tight Junction - interlocking junctional proteins-Desmosome -linker proteins (cardiac cells)-Gap Junction - transmembrane proteins-Membrane Transport:-Passive processes-Diffusion (Concentration Gradient)Simple diffusion - directly through lipid bilayer, non-polar, hydrophobic substances (ex. O2 & CO2 - diffuses into cells & out of cells)Facilitated diffusion - substances go down their concentration gradient through membrane proteins (transport or carrier proteins - polar, hydrophilic & cannot cross lipid bilayer w/o carrier proteins), Exhibits a. Specificity - carrier proteins for glucose will not transport amino acids, andvice versab. Saturation - once all the carrier proteins are engaged, maximum transport of the substance is reached (even when a concentration gradient still exists)Osmosis - low concentration --> high concentration, through a semi-permeable membrane, the plasma membrane acts as a selective membrane "semi-permeable" in allowing water to move across through holes called aquaporins, b/c water is a polar covalent molecule, water movement from low [solute] --> high [solute], high [H2O] --> low [H2O]-Filtration (Pressure Gradient)Passive process (no energy input), higher pressure --> lower pressure -Active processesEnergy (ATP) required to move substances across plasma membrane-Active transport ("solute pumping" - Solute Concentration)Movement of solutes/ions from lower [solute] --> high [solute] (against concentration gradient), requires a carrier (transport) protein in the plasma membrane b/c ions are moved (charged particles - anions & cations) and cannot go through the lipid bilayer and the plasma membrane, specificity & saturation-Vesicular transport Substances moved, enclosed in vesicles, membrane without glycocalyxExocytosis - Movement of substances enclosed in vesicles from interior to exterior (This is how hormones and enzymes are secreted from cells)Vesicle that fuses with the plasma membrane is used in endocytosis to move substances into the cell.Endocytosis - Movement of substances from exterior to interior of cell-Phagocytosis - Movement of solid particles (clumps of bacteria or cell debris) enclosed in vesicles by formation of pseudopods, vesicles pinched off into cytoplasm of the cell)Phagosomes - Vesicles that bring particles inPhagocytes - Lysosomes (powerful digestive enzymes - lysozymes) fuse with phagosomes to digest phagosomes & contents, lysozymes destroy/digest the contents of phagosomes, few cells can undergo this process (these cells are phagocytes), due to their functions they contain high levels of lysosomesUltimate Phagocyte = Macrophages-Pinocytosis - Movement of liquid solution (bulk-fluid endocytosis)Solution is taken into the cell enclosed in vesicles (vesicles pinch off into the cytoplasm - pinocytic vesicles - coalesce with lysosomes and released into the cytoplasm), will contain nutrients required by the cell-Receptor-mediated endocytosis - Specific substances bind to specific receptors (membrane receptors) on cell surface, pits transport substancesinto cell, involution (inward folding) of that part of the plasma membrane (vesicle called a Coated Pit is formed and released into the cytoplasm, covered by bristle-like structures called Clathrin - Must be removed before coated pits coalesce with lysosome and the content released into the cytoplasm)-Specificity and saturation2 active processes: Active transport & Receptor-mediated endocytosis1 passive process: Facilitated
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