Ch 8 Metabolic Pathway o Begins with a specific molecule which is then altered in a series of defined steps resulting in a certain product Metabolism totality of an organism s chemical reactions Catabolic Pathways breakdown pathways cellular respiration o Pathways can have more than one starting molecule and or product o Energy that was stored in the organic molecules becomes available to do the work of the cell such as ciliary beating or membrane transport Anabolic Pathways consume energy to build complicated molecules from simpler ones sometimes referred to as biosynthetic pathways synthesis of an amino acid from simpler molecules and synthesis of a protein from amino acids o Energy released from the catabolic pathways can be stored and then used to drive anabolic pathways Energy the capacity to cause change o Kinetic energy energy associated with relative motion of objects o Thermal energy heat kinetic energy associated with the random movement of atoms or molecules Light is a type of energy that can be harnessed to perform work such as pioneering photosynthesis in green plants o Potential energy an object not presently moving may still possess energy This happens because of location or structure Think of water behind a dam o Chemical energy a term used by biologists to refer to the potential energy available for release in a chemical reaction Think about catabolic pathways release energy y breaking Thermodynamics down complex molecules o Study of energy transformations that occur in a collection of matter First law Energy can be transferred and transformed but it cannot be destroyed 2nd law answers What happens to the energy after is performs work Second law Every energy transfer or transformation increases the entropy of the universe for a process to occur spontaneously it must increase the entropy of the universe During every energy transfer or transformation some energy becomes unavailable to do work A system can put heat to work only when there is a temperature difference that results in the the heat flowing from a warmer location to a cooler one Loss of usable energy during energy transfer or transformation is that each such event makes the universe more disordered o Entropy is a measure of disorder or randomness In many cases increased entropy is evident in the physical disintegration of a system s organized structure You can observe an increase in entropy in an unmaintained building The concept of entropy is important to understand to be able to understand why certain processes occur without the input of energy o For a process to occur without outside help it must increase the entropy of the universe Spontaneous process Free Energy is the portion of a system s energy that can perform work when temperature and pressure are uniform throughout the system as in a living cell o H symbolizes change in enthalpy enthalpy total energy o S is the change in the system s entropy o T is the absolute temperature in Kelvin units o G is the change in free energy to calculate free energy use the following equation G H T S o processes with a negative G are spontaneous for G to be negative either H must be negative the system gives up enthalpy and H decreases OR T S must be positive Free energy Stability and Equilibrium o G represents the difference between free energy of the final state and free energy of the initial state G Gfinal state Ginitial state So G can be negative only when the process involves a loss of free energy during the change from initial state to the final state A process is spontaneous and can perform work only when it is moving toward equilibrium Free Energy and Metabolism o Exergonic reaction energy outward proceeds with a net release of free energy G is negative for an exergonic reaction use the overall reaction for cellular respiration as an example C6H12O6 6 O2 6 CO2 6 H2O o G 686 kcal mol 2 870 kJ mol o Endergonic reactions absorbs free energy from its surroundings This kind of reaction stores free energy in molecules G increases G is positive Cells do three kinds of work o Chemical work o Transport work o Mechanical work The active site and the catalytic cycle of an enzyme 1 Substrates enter the Active site enzyme changes shape such that its active site enfolds the substrates 2 Substrates are held in active sites by weak interactions such as hydrogen bonds and ionic bonds 3 Active sight can lower activation energy and speed up the reaction 4 Substrates are converted to products 5 Products are released 6 Active site is available for two new substrate molecules Induced fit brings chemical groups of the active site into position that enhance their ability to catalyze the chemical reaction Active site a pocket or groove on the surface of the enzyme where catalysis occurs The efficiency of an enzyme is effected by environmental factors such as pH o Each enzyme has optimal conditions that it works better under For example up to a point the rate of an enzymatic reaction increases with increasing temperature but above that temperature the enzymatic reaction drops sharply o Cofactors non protein helpers for catalytic activity may be bound tightly to an enzyme as permanent residents or may bind loosely and reversibly If the cofactor is organic it is a coenzyme Enzyme inhibitors o Normal a substrate can bind normallyto the active site of an enzyme o Competitive a competitive inhibitor mimics the substrate competing for the active site o Noncompetitive binds to the enzyme away from the active site altering the shape of the enzyme so that even if the substrate can bind the active site functions less effectively Allosteric Regulation term used to describe any case in which a protein s function at one site is affected by the binding of a regulatory molecule to a separate site o Cooperativity a kind of allosteric regulation a substrate molecule binding to one active subunit in a multisubunit enzyme triggers a shape change in all subunits Feedback inhibition a metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway Ch 9 o Lactic acid o alcohol Fermentation is partial degradation of glucose without the use of oxygen Cellular Respiration a more complete breakdown of glucose Redox reactions one substance partially or totally shifts electrons Oxidation the loss of electrons from one substance Reduction is the addition of electrons Electron Transport Chain consists mostly of proteins built into the inner membrane
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