BCH1001 Cell Biology 3 - PDF

Cell Biology 3 Dr Patricia Johnson [email protected] Cell communication - Extracellular and intracellular receptors Most signalling molecules are hydrophilic and cannot cross plasma membrane – they b...

Cell Biology 3 Dr Patricia Johnson [email protected] Cell communication - Extracellular and intracellular receptors Most signalling molecules are hydrophilic and cannot cross plasma membrane – they bind to cell surface receptors Some small molecules can diffuse across membrane and bind intracellular receptors Cells can communicate by receiving signals Ø WATER IS AN EXCELLENT SOLVENT Water can dissolve a greater variety of substances in greater quantity than can any other solvent. This promotes chemical reactions and is due to water’s chemical nature – it is a polar substance Ø WATER HAS HIGH SURFACE TENSION & CAPILLARITY resulting from bonds between water molecules. This allows it to serve as a transport medium Ø WATER REGULATES TEMPERATURE due to its high heat capacity [helps maintain body temperature] and high heat of vaporization [evaporation of sweat helps to cool the body] WATER HAS A NEUTRAL pH – Is neither acidic nor basic [alkaline] DIFFUSION - The tendency of dissolved or suspended particles to move from one place to another due to their heat energy [thermal agitation] generally from a high concentration to a low concentration OSMOSIS – Movement of a substance [usually water] through a semi-permeable membrane along a concentration gradient DIALYSIS – Movement of solutes through a semi- permeable membrane to bulk solvent from an area of High concentration to an area of low concentration. Ø THESE ARE PASSIVE PROCESSES – do not need energy, are “downhill” Diffusion: net movement of a substance from a region of greater to lower concentration http://www.youtube.com/watch?v=IaZ8Mt F3C6M Osmosis: water passes through selectively permeable membrane from region of higher concentration to lower  Concentration of dissolved substances (solute) in a solution (solvent) usually water Isotonic: equal solute concentration Hypertonic (lots of solute) outside: loses water in plasmolysis Hypotonic (low solute) outside: gains water and swells Response of animal cells to osmotic pressure Dialysis  Dialysis http://www.youtube.com/watch?v=IaZ8MtF 3C6M http://www.youtube.com/watch?v=shFSW8VE 3Gs http://www.youtube.com/watch?v=al3plwg SqL0 http://www.youtube.com/watch?v=71XNJe kYV5o http://www.youtube.com/watch? v=q09QraVPZ7k Facilitated diffusion Occurs down a concentration gradient http://www.youtube.com/watch? v=vKGN_Zhz8AY  Active transport Moves ions or molecules against a concentration gradient http://www.youtube.com/watch?v=yz7EHJFDEJs http://www.youtube.com/watch? v=kfy92hdaAH0  Transport across the plasma membrane Outer membrane Inner membrane ATP Passive diffusion Facilitated transport Active transport