Unit 3 Smallest unit of living organisms Four basic parts of the cell Cell membrane encloses the cell Nucleus houses genetic material Cytoplasm- fills the cell (mostly water) Organelles specialized structures in cell Thin, flexible, elastic Selectively permeable Oxygen & Carbon Dioxide diffuse easily and are soluble in lipids Small polar (H2O) small enough to pass between lipid molecules (aquaporins) Large water soluble molecules and ions cannot pass without help Lipid Bilayer Phospholipids Hydrophobic tails Hydrophilic heads Cell Membrane Structure carrier protein protein channel Globular proteins carbohydrate phospholipid bilayer Fibrous Proteins Cholesterol molecule Passive Mechanisms no energy required Molecules move down their concentration gradient. Diffusion- Random movement of molecules molecules move from high concentration to low concentration until equilibrium is reached Diffusion high concentration low concentration Osmosis- water moves across a semi- permeable membrane from low solute concentration to high solute concentration Isotonic solution Two solutions with same solute concentration Hypotonic solution Solution with lower solute concentration and higher water concentration Hypertonic solution Solution with higher solute concentration and low water concentration 1 = Isotonic no net movement of water Normal state for animal cells 2 = Cell- hypertonic; environment hypotonic Water enters cell; cell swells & burst Cytolysis; cell dies 3 = Cell- hypotonic; environment hypertonic Water exits cell; cell shrinks & dies Filtration small molecules forced to move through membrane Tissue Fluid: -result of filtration -composed of water & small dissolved substances Force used: -Blood pressure -hydrostatic pressure Facilitated diffusion- Diffusion of solutes across membrane with help of transport proteins (channel/carrier) Passive transport Transport proteins are specific Model Protein has 2 conformations Solute binds to protein Protein changes shape Solute released to other side of membrane Facilitated Diffusion high concentration low concentration Requires cell energy (ATP) Materials moved against concentration gradient (low to high) Pumps Molecule or ion combine with carrier protein Shape of carrier protein changes with the help of energy (ATP) Particle is able to move against the concentration gradient Other examples: Sugar, amino acids sodium, potassium, calcium, hydrogen ions Endocytosis (1-4) Intake of large molecules, solids, food Material collects in pocket of cell membrane Pocket pinches off forming vesicle Exocytosis (5-8) Release of large molecules, solids, wastes from cell Vesicle fuses with cell membrane Contents released to outside Cell eating Intake of solids, food, bacteria nonspecific Cell drinking Intake of small droplets of liquid (oil) nonspecific Specific Model (picture) Molecule binds to receptor protein Complex migrates to coated pit Pit pinches off forming vesicle Receptor protein returns to cell membrane