2An Introduction to Metabolism The chemistry of life is organized into metabolic pathwaysThe totality of an organism’s chemical reactions is called metabolismEnzymes selectively accelerate each step
3An Introduction to Metabolism Catabolic pathways release energy by breaking down complex molecules to simpler compounds.This energy is stored in organic molecules until it needs to do work in the cell.Anabolic pathways consume energy to build complicated molecules from simpler compounds.The energy released by catabolic pathways is used to drive anabolic pathways.
4Organisms transform energy Kinetic energy is the energy of motion.Potential energy is the energy that matter possesses because of its location or structure.
5Organisms transform energy Energy can be converted from one form to another.Problem: A waiter walks across the room, turns on a switch and the light comes on.How is energy converted? How is photosynthesis and respiration involved?
6Are organisms opened or closed systems? Explain The energy transformations of life are subject to two laws of thermodynamics1st Law – Energy is conserved2nd Law – Energy transformations cause disorderAre organisms opened or closed systems? Explain
7Entropy is a quantity used as a measure of disorder, or randomness. Organisms live at the expense of free energyFree energy is the portions of a system’s energy that is able to perform work when temperature is uniform throughout the system
8Endergonic ReactionsAn endergonic reaction is one that absorbs free energy from its surroundings. G is positiveIf cellular respiration releases 686 kcal, then photosynthesis, the reverse reaction, must require an equivalent investment of energy G = kcal / mol
9Exergonic ReactionsAn exergonic reaction proceeds with a net release of free energy and G (Change in Free Energy) is negativeFor the overall reaction of cellular respiration:C6H12O6 + 6O2 -> 6CO2 + 6H2O G = -686 kcal/mol
11ATP powers cellular work ATP (adenosine triphosphate) is a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups.Hydrolysis of the end phosphate group forms adenosine diphosphate [ATP -> ADP + Pi] and releases 7.3 kcal of energy per mole of ATP under standard conditions.
12ATP/ADP CycleATP is a renewable resource that is continually regenerated by adding a phosphate group to ADP
14Check Yourself Questions What is the difference between a catabolic reaction and anabolic reaction?How does the 1st and 2nd law of thermodynamic relate to living organisms?Why is ATP important to metabolism?Describe the ATP-ADP process.How is the 2nd law of thermodynamics related to evolution
15EnzymesEnzymes are biological catalysts that speed up metabolic reactions by lowering energy barriersA catalyst is a chemical agent that changes the rate of a reaction without being consumed by the reaction
16All reactions must absorb energy in order to move from reactant to product The amount of free energy absorbed is called the activation energy (EA)
18Enzymes are substrate specific Substrate – a reactant that binds to an enzymeActive Site – a pocket or groove on the surface of the enzyme in which the substrate fitsInduced fit – As the substrate binds, the enzyme changes shape leading to a tighter fit
20Mechanism used by enzymes to speed up reactions: The active site orients and binds substrates in the correct orientation for the reaction.R groups create a conducive environmentEnzymes can form covalent bonds with the substrate in an intermediate step
21Check Yourself Questions Define the following terms:Catalyst, Active site, substrate, induced fitWhat are the first and second laws of thermodynamics?What is the difference between an anabolic reaction and a catabolic reaction?What is the difference between endergonic exergonic reaction? Is G positive or negative for each?
27The control of metabolism Allosteric Regulation – In many cases, the molecules that naturally regulate enzyme activity behave like reversible noncompetitive inhibitors.These molecules often bind weakly to an allosteric site, a specific receptor on the enzyme that is not the active site.
29The control of metabolism One of the common methods of metabolic control is feedback inhibition in which a metabolic pathway is turned off by its end product.The end product acts as an inhibitor.
30Feedback InhibitionWhen the product is abundant the pathway is turned off, when the product is rare it is active.
31Check Yourself Questions Describe the induced fit model.What is the substrate and active site?What environmental factors help to control the reaction of enzymes?How are coenzymes different than inhibitors?Describe the different types of inhibitors.