Biology Unit 2 09 25 2013 Special structures help cells to communicate Four types of connections between cells Desmosomes Link adjacent cells to prevent tearing as organisms move Complexive proteins and intermediate filaments Animal cells only Tight junctions Gap junctions Make cell attachments leak proof Animal cell only Stitch membranes together Channels that connect the cytoplasm of adjacent cells Hormones ion nutrients and electrical signals can pass through channels Only in animal cells Plasmadesmata Holes in the walls of adjacent cells Lined with plasma membrane Water nutrients hormones etc passes freely between cells Plant cells only Ex Roots trying to pass nutrients and water up the rest of the plant Chapter 6 Energy Flow in the Life of a Cell 09 25 2013 Energy the capacity to do work Work the transfer of energy into an object causing it to move Chemical energy energy contained within molecules and released by chemical reactions Stored molecules such as glycogen and fat Converted to ATP and used to perform work Potential Energy Stored energy o Chemical energy stored in bonds ATP or sugars o Electrical energy stored in a battery o Positional energy stored in an object like the penguin in 6 1 gravity can pull him down dependent on where you are placed Kinetic Energy The energy of motion o Light energy Movement of photons o Heat energy Movement of molecules o Electricity Movement of electrically charged particles o The movement of larger objects Penguin Kinetic energy can be transformed into potential energy and vice versa o Cliff jumper o Photosynthesis taking kinetic light energy and transferring it to potential energy in ATP The laws of thermodynamics First law of thermodynamics o Energy can neither be created nor destroyed by ordinary processes o Also called the low of conservation of energy o Nuclear reactions are an exception to this law Matter is converted to energy The second law of thermodynamics o When energy is converted from on form to another amount of useful energy decreases o In other words no energy conversion process is 100 efficient A car only converts about 25 of the potential energy stored in gasoline to kinetic energy of the car moving The other 75 is lost as heat o Useful energy is stored in an organized matter o As energy is used randomness and disorder increase Ex Gasoline is converted to CO2 and H20 as it burns Glucose is converted to CO2 and H20 as it burns o Entropy the tendency towards loss of complexity order and useful energy and the increase in randomness disorder and less useful energy Chemical reaction a process that creates or breaks chemical bonds between atoms o Converts reactants into products Two types of chemical reactions o An exergonic reaction releases energy o An endergonic reactions requires energy Exergonic reactions Spontaneous reactions Release energy downhill reactions o From high energy reactants to low energy products o Ex Athletes using glycogen and glucose gets broken down and then you sweat and use ATP Endergonic reactions Non spontaneous reactions Require a net input of energy uphill reactions o From low energy reactions to high energy products o Energy comes from an outside source o Photosynthesis Activation energy All chemical reactions require energy to get started Why do reactions need activation energy o All atoms are surrounded by electrons o In order for a chemical reaction to occur the electrons have to interact o Negatively charged electrons must be forced together o Once they touch then the reaction is going to occur Kinetic energy moving molecules can provide activation energy for exergonic reactions In general the speed at which a reactions occurs is determined by its activation energy o Activation energy is required for all chemical reactions because Energy transport within cells Performed by energy carrier molecules Most cells use glucose as their main fuel Glucose cannot provide endergonic reactions directly Energy released by glucose is transferred to energy carrier molecules Energy carrier molecules unstable molecules synthesized at the site of an exergonic reactions Not used for long term storage Some exergonic reactions transfer released energy to electrons NAD NADH Capture energy and hydrogen ions Represented in cytoplasmic FAD FADH2 fluid Cells use energy released by exergonic reactions to drive endergonic reactions Enzymes and biochemical reactions In biological systems enzymes act as catalysts to promote reactions that have high activation energies Catalysts Ex enzyme o Speed up reactions o Can speed up o increased speed can create sufficient force to overcome activation energy and sugar will burn o Are not consumed or permanently changed by reactions Enzymes are biological catalysts enzymes act as a catalyst to promote reactions that have high activation energy Most are proteins Highly specific for a certain reaction Both reactions are catalyzed by enzymes ADP P ATP Synthase ATP ATPase Each enzyme has an active site into which one or more reactants also called substrates can enter The enzyme sucrase catalyzes the conversion of sucrose to glucose fructose Coenzymes o non protein molecules that help some reactions occur o many are synthesized from vitamins Sugar can burn rapidly if ignited combining with oxygen to create carbon dioxide and water the same reaction occurs in your body but happens in steps controlled by enzymes the breakdown and synthesis of all molecules within the cell occurs in steps o each step is controlled by different enzymes Metabolism is the sum of all chemical reactions in a cell Metabolic pathways o Initial reactant goes through multiple steps of modification each y a different enzyme o Involved in both the synthesis and breakdown of molecules ex Glycolysis and photosynthesis o Different metabolic pathways often use some of the same molecules so all of the thousands of metabolic pathways in a cell are directly or indirectly interconnected Cells must regulate their metabolic reactions Cells can regulate enzymes in order to regulate the rate of chemical reactions o Regulation of enzyme synthesis o Regulation of enzyme activity Regulation of enzyme synthesis o The amount of substrate Reactant or the amount of enzyme can effect the rate of reactions More substrate Enzyme faster reactions Increases substrate building with active site Rate of reaction increases until all active sites are occupied o An increase in either subtract or enzyme concentration can increase the rate of
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