Lecture 10Outline of Last Lecture I. MetabolismII. Metabolic PathwaysIII. Types of PathwaysIV. EnergyV. Energy with Chemical ReactionsOutline of Current Lecture I. Chemical ReactionsII. Exergonic ReactionsIII. Endergonic ReactionsIV. EnzymesV. Enzyme-Substrate ComplexVI. Factors Affecting Enzyme ActivityVII. Control of MetabolismVIII. ATPCurrent LectureI. Chemical Reactionsa. Reactant molecules form to productsi. Written as: reactants  productsb. Chemical reactions proceed with change in free energy (G)i. Free energy (G) is the amount of energy available to do workii. Free energy includes enthalpy and entropy factors (lecture 9)iii. Written as: ∆ G=∆ H − T ∆ S, where ∆ G is the change in free energy, ∆ H is the change in enthalpy, and T ∆ S is the change in entropyiv.∆ G determines whether the reaction is spontaneousII. Exergonic Reactions BIOL 1st Editiona. Spontaneousb. Reactants have more bond energy (H) than productsi. Energy is releasedc. S increases during the reaction because products are more disorderedd.∆ G is the maximum amount of work that reaction can do (-)e.III. Endergonic Reactionsa. Not spontaneousb. Reactants have less bond energy (H) than products (energy is consumed)c. S tends to decrease during the reaction (products are more ordered)d.∆ G is the minimum amount of work required to make a reaction go (=)e.IV. Enzymesa. Biological catalysts made from proteins that speed up chemical reactions in the cellb. Catalyst – speeds up a reaction without being used in the reaction over and overc. Enzymes are used to bring the reaction to the transition stated. Enzymes speed up the reaction, but don’t change the free energy (∆ G)e. Chemical reactions utilizing enzymes refer to the reactants as “substrate”i. Substrate is held in a 3-D pocket in the enzyme specific to its shapeii. This pocket is referred to as the “active site”V. Enzyme-Substrate Complexa. Binding the substrate and the active site induces the enzyme to change shapeb. This stresses the bonds in the substrates or brings the two of them togetherc. Chemical reactions occur in the active sited. Products are released, allowing the enzyme to catalyze another reactione. Occurs very quicklyVI. Factors Affecting Enzyme Activitya. Environmental conditionsi. Temperatureii. pHiii. Ionic concentrationb. Cofactors and coenzymesi. Small non-protein molecules that are required for the activity of some enzymesii. Inorganic (iron/zinc) or organic (vitamins)c. Substrate concentrationi. Higher concentration increases the rate of reactionii. When all active sites are filled, the solution has reached saturationiii. Saturation = maximum rate of reactiond. Enzyme inhibitorsi. Competitive inhibitors – chemical that looks like an enzyme and competes for the active siteii. Noncompetitive inhibitor – binds to another part of the enzyme and changes its shape so it can’t bind with substratee. Allosteric regulationsi. Some enzymes are regulated by the binding of small molecules to a specific site on the enzyme1. Allosteric site – where these molecules are bonded (NOT the active site)ii. These enzymes usually have more than one subunit and are called “allosteric enzymes”iii. Allosteric enzymes oscillate between an active form (catalyzes chemical reaction) and an inactive form (doesn’t bind to the substrate or catalyze the reaction)iv. Two types of regulators:1. Allosteric activator – stabilizes active form, increasing activity2. Allosteric inhibitor – stabilizes inactive form, decreasing activityVII. Control of Metabolisma. Metabolic pathways are a series of chemical reactions in which the product of one reaction becomes the reactant for the nextb. Can be controlled by controlling one enzymec. Feedback Inhibition  example of controlling a pathwayi. The end product of the pathway is an allosteric inhibitor of an enzyme that functions early in the pathway (enzyme 1 usually)ii. Ex: Threonine converting to Isoleucine1. Cell needs both amino acids to make proteins2. If too much isoleucine is present, the cell runs our of threonine, so the isoleucinebinds to the inactive form of enzyme 1 and inhibits it, allowing threonine to accumulate3. This pathway is self-controlling because the end product regulates its own synthesis4. Good mechanism for reactions that have an important product to reactant ratioVIII. ATPa. Adenosine triphosphate (ATP) is the usual immediate source for cellular work b. ATP and ADP release phosphates, causing the molecule to become energized, and allowing the cell to do workc. The regeneration of ATP is an endergonic reaction through two ways:i. Cellular respiration – catabolic pathwayii. Photosynthesis – light