Cell Membrane-Structure and Function

Transcription

1 Cell Membrane-Structure and Function BIO 250 Living things are composed of cells and cell products (extracellular) Cells are the basic unit of structure They are the basic unit of function They vary in size, shape and function Shape related to function RBC shape gives large surface area for gas exchange Nerve cell (neuron) has long threadlike fiber to communicate over long distance Adult human has about 75 trillion cells. Cell membrane Separates outside from inside cell Selectively permeable Composed primarily of phospholipids and proteins with some carbohydrates, cholesterol and ions Plays a role in intercellular communication 1 1

2 2 2

3 In the fluid-mosaic model the cell membrane is a Lipid Bilayer Membrane phospholipids have a polar hydrophilic head H l h d h bi t il Have a non polar hydrophobic tail Membrane proteins include these types: Integral proteins embedded within bilayer Peripheral proteins attached to surface Glycoproteins with associated carbohydrates 3 3

4 Back 4 4

5 Back Back 5 5

6 Back Back Cell membrane Controls movement of molecules into and out of the cell Lipid soluble molecules dissolve through the lipid portion of the membrane Water soluble substances (Small) may ypass through protein channels which are:» Passive channels (leak channels)» Active channels (gated channels) Water soluble substances (Large) may be transported by carrier proteins:» Passively by facilitated diffusion carriers» Actively by active transport carriers 6 6

7 Movement of Materials Through Membranes Involve physical or physiological processes Gradients typically present Several processes involved Diffusion Random motion of solutes in a solution Involves concentration gradient Concentration gradient is a measure of the difference in concentration of a solute in a solvent between two points divided by distance between the two points. Factors affecting speed of diffusion Concentration of molecules Particle size and weight Temperature Diffusion through a leak channel 7 7

8 Facilitated Diffusion Scattering of molecules Involves concentration gradient Involves a cell membrane Involves specific protein carrier Does not require expenditure of energy by cell Osmosis Involves diffusion of water Through a selectively permeable membrane Requires a concentration gradient Water diffuses through membrane from side with high water concentration to side with lower water, OR Water diffuses through membrane from side with low solute concentration to side with higher solute. 8 8

9 Tonicity of Water By OSMOSIS, cells can gain or lose water causing them to shrink or swell: Cells gain water in hypotonic solutions (lysis) Isotonic solutions have same water concentration as cells Cells lose water in hypertonic solutions (crenation) Active Transport Involves a cell membrane Involves a specific protein carrier Involves expenditure of energy by cell Materials can be moved against gradient and concentrated within the cell Filtration Requires filtering membrane Requires solution with mixture of particle sizes Requires hydrostatic pressure e.g. blood is filtered through capillary wall pushed by blood pressure 9 9

10 Colloid Osmotic Pressure (COP) Interstitial fluid is returned to blood by osmotic pressure of blood proteins. Filtration and COP are opposing forces Forces are not balanced Exo- and Endocytosis More massive materials can be moved Exocytosis Endocytosis 10 10

11 Phagocytosis/Pinocytosis Particulate matter can brought into the cell by endocytosis. Cells that regularly eat material from outside are called phagocytes (cells that eat) If the material brought into the cell by endocytosis is soluble material the process is called pinocytosis (pino- to drink) 11 11