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Transcript
2-Basis of Cell Structure and Function Taft College Human Physiology Basis of Cell Structure and Function • Last time we spoke of the cell as the basic unit of function. • For the next couple of weeks we will continue to talk about things at the cellular level- cells and their qualities. • We spoke last time about characteristics of living cells or what living cells do: • Intake, metabolism (anabolism and catabolism), output (elimination of wastes), reproduction, movement, growth, responsiveness. • Although each of your 100 trillion cells exhibit each of these characteristics that does not mean that all of your cells are exactly the same. Basis of Cell Structure and Function • In multicellular organisms we tend to see a division of labor, or specialization, amongst the cells. That is, the different cells within the body perform different jobs for functions. • Due to the differences in function of the cells we are can see great diversity in cell: • 1. Size • 2. Shape Of Cells • Cell Size • Cells vary in size from the smallest bacteria (1 micrometer) to the largest cell, an ostrich egg. • There are certain limits that are placed on cell size. Cells cannot be infinitely larger or infinitely small. There are Limits to Cell Size • Cells can’t be infinitely small • They must be at least large enough to contain macromolecules (proteins and nucleic acids – DNA) that are necessary to sustain life. • Cells can’t be infinitely large • 1. Cells must be small enough for the nucleus to control cellular activities. The largest cells in your body “cheat” in this respect by being multinucleated. • 2. Cells must be small enough for efficient movement of nutrients into the cell and movements of wastes out of the cell. Cell Shape is Related to Cell Function • The cells that line blood vessels and alveoli are shaped very flat and thin. The thin shape of cells (simple squamous epithelium) allows for passage of materials (O2, CO2) through the cell. • Cells that absorb things typically have microvilli. Microvilli increase surface area for absorption to occur. Microvilli increase the amount of absorptive area significantly without increasing the amount of cytoplasm. • Biconcave shape of an RBC creates maximum surface area for the rapid diffusion of oxygen and carbon-dioxide throughout the cell. How do things move in and out of cells? • Things may move through cell membranes by Passive Processes • Passive Processes do not require energy use by the cell and include: • 1- Diffusion • 2- Osmosis • 3- Bulk Flow • 4- Facilitated Diffusion How do things move in and out of cells? • • • • Things may move through cell membranes by Active Processes Active Processes do require energy use by the cell and include: 1- Active Transport 2- Vesicular Transport A. Endocytosis 1. Pinocytosis 2. Phagocytosis 3. Receptor mediated endocytosis B. Exocytosis Passive Processes • 1. Diffusion • Diffusion is the movement of molecules from an area of high concentration of those molecules to an area of low concentration of those molecules • Molecules move from [High] to [Low] Diffusion The movement of the molecules is caused by the kinetic energy of the molecules. Kinetic energy = energy of movement Example: Dye crystal in water. Dye will first be concentrated around the crystal. Slowly the dye moves away from the concentrated source until the molecules become equally distributed in the container at which time they are said to be in dynamic equilibrium. Dynamic Equilibrium • If molecules reach equal distribution or concentration of molecules throughout a container, they are said to be in dynamic equilibrium. • In dynamic equilibrium, do the molecules stop moving? • No – the molecules still have kinetic energy and continue to move in random motion • In dynamic equilibrium, there is no net movement of molecules. Rate of diffusion is influenced by: • 1. Temperature • The greater the temperature, the greater the rate of diffusion. • Why? • Increased temperature increases the kinetic energy (energy of motion) of the molecules causing them to move faster. Rate of diffusion is influenced by: • 2. Concentration gradient (difference) • The greater the concentration difference, the greater the rate of diffusion • Why? • Molecules follow the path of least resistance • It easier for molecules to move from higher concentration to lower concentration as there are fewer molecules to run in to. B A C Rate of diffusion is influenced by: • 3. Size of the diffusing molecule • The greater the size of the molecule, the slower the rate of diffusion. • Why? • The larger the molecule, the greater it’s chances of running into other things which slows it down. (Golf ball vs Basketball?) Passive Processes • 2. Osmosis • Osmosis is the movement of water molecules from an area of high concentration of those molecules to an area of low concentration of those molecules through a semi-permeable (selectively permeable) membrane. • Water molecules move from [High] to [Low] through semi-permeable membrane. • Osmosis is a specialized type of diffusion. ChemTerms - Review • What is a solution? • A solution is a mixture of a solute (solid) and a solvent (dissolving liquid). • Example Tea + water = solution solute + solvent Osmosis Understanding Osmosis • It’s your first day on the job in a blood lab • Your boss has asked you to wash the red blood cells in a blood sample – • How do you do it? • Distilled water? • What would happen if you used distilled water? ChemTerms – Review and Osmosis • What is tonicity? • Tonicity = solute(solid) concentration • Understanding this term will help us make sense of some other important terms. ChemTerms – Review and Osmosis • Isotonic Solution • =same solute concentration (and same water concentration) as the cell • = 0.9% NaCl in the RBC • In a clinical setting, isotonic saline has the same solute concentration as the contents of an RBC = 0.9% NaCl. ChemTerms – Review and Osmosis • Hypotonic Solution • =lower solute concentration (and higher water concentration) than the cell • = any solution less than 0.9% salt. • Exposing RBC’s to a hypotonic solution (like distilled water) will cause them to swell and burst = hemolysis ChemTerms – Review and Osmosis • Hypertonic Solution • =higher solute concentration (and lower water concentration) than the cell • = any solution greater than 0.9% salt. • Exposing RBC’s to a hypertonic solution will cause them to lose water and shrink = Crenation Understanding Osmosis Understanding Osmosis Passive Processes • 3. Bulk Flow • Bulk Flow is the movement in the same direction, of large numbers of molecules due to gravity or pressure. • Example outside of the body? • Water in river • Example in the body? • Blood in blood stream, air in respiratory passages Passive Processes • Bulk Flow of materials through a permeable membrane is called Filtration. • Ex. – passage of materials through capillary walls due to blood pressure. • The nephrons in the kidney are responsible for (non-selective ) filtration. Passive Processes • 4. Facilitated diffusion • Facilitated diffusion is diffusion of a substance with the help of special transporter proteins in the cell membrane. • Transporter proteins are helpful when substances are too lipid insoluble to diffuse through the plasma membrane. • Ex. Glucose is moved across the cell membrane by transporter proteins. Insulin serves to speed up the rate of facilitated diffusion of glucose by increasing the number of transporter proteins to move sugar into the body cells where it is needed. Active Processes • Active processes require energy expenditure (ATP) by the cell. • 1. Active Transport • 2. Vesicular Transport • Next Time!