Cellular Level Wednesday September 12 2012 12 19 PM Cells 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 Level Cells are the structural units of all organisms reactions occurring inside cells sustain the organism In 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 function Function of a cell also depends on the type of subcellular structures present theme of compartmentalization at the cellular level 3 Parts to Cell Membrane Proteins 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 Integral proteins surface of plasma membrane Peripheral proteins attached to integral proteins heads on cytoplasmic face of plasma membrane Functions Transport Enzymatic activity receptors intercellular joining cell cell recognition attachment to the cytoskeleton Membrane proteins Integral proteins exposed on both sides of the plasma membrane Transmembrane Peripheral proteins Carrier transport protein exhibit specificity carrier mediated transport exhibit saturation Functions of membrane proteins Facilitated diffusion Active transport Membrane 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 of the 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 and vice versa b 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 Pressure Gradient Filtration Passive process no energy input higher pressure lower pressure Active processes Energy 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 Substances moved enclosed in vesicles membrane without glycocalyx transport Exocytosis 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 Movement of solid particles clumps of bacteria or cell Phagocytosis debris enclosed in vesicles by formation of pseudopods vesicles pinched off into cytoplasm of the cell Phagosomes Vesicles that bring particles in Phagocytes 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 lysosomes Ultimate Phagocyte Macrophages Pinocytosis 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 receptors membrane receptors on cell surface pits transport substances into 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 Movement of liquid solution bulk fluid endocytosis Specific substances bind to specific Specificity and saturation 2 active processes Active transport Receptor mediated endocytosis 1 passive process Facilitated diffusion Special Transport Systems Transcytosis Movements of enclosed substances across the cell released on the opposite side endocytosis travel across cell to opposite side to exocytosis Endothelial cells lining the internal surface of blood vessels take substances from the blood via endocytosis substances
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