Energy and Enzymes (metabolism)

1. Energy and Enzymes(metabolism) Chapter 8.1, 8.2, 8.4, 8.5

2. metabolism is the process of breaking down and creating molecules necessary for life • each step in this process is driven by an enzyme which directs the speed of the reaction (enzymes are proteins!) • catabolic--breakdown molecules • cellular respiration • anabolic--build molecules • protein synthesis

3. energy is the capacity to cause change • kinetic (heat) vs. potential (chemical) • thermodynamics = energy transformations • 1st law (matter cannot be created or destroyed, only change form) • 2nd law (energy transfer increases the entropy of the universe) • spontaneous reactions vs. reactions that need energy

4. free energy--identifies if a reaction requires energy to proceed • higher free energy = unstable • does not require outside energy for the reaction to happen (spontaneous) • exergonic reaction (negative delta G) • does not imply that it happens fast! • lower free energy = stable • requires outside energy for the reaction to proceed (nonspontaneous) • endergonic reaction (positive delta G)

5. Enzymes • Lower energy barriers for the reaction to happen at an increased rate (catalyst); not used up during the reaction • activation energy (energy required to get reaction going) • based on how difficult it is to break the chemical bonds • speed up reactions that would occur anyway

6. How enzymes work...(induced-fit model) • substrate (reactant an enzyme acts on) • enzyme binds to substrate, forming enzyme-substrate complex • each enzyme has a specific substrate (results from unique sequence of amino acids) • active site (region of enzyme where substrate binds) • when this occurs, the shape of the enzyme changes which enhances the reaction

7. Rate in which enzyme converts substrate to product is determined by... • the initial concentration of the substrate (or enzyme) • more substrate molecules that are available the more frequently they access active site. • limited by the enzyme concentration (saturated when rate of reaction is determined by how often substrate can move into active site) • general environmental factors • temperature, pH, and other chemicals • each enzyme has optimal environment depending on the organism and where it needs to work

8. Enzyme Inhibition and Regulation • competitive inhibition • reduce the productivity of enzymes by blocking substrate from entering active site • overcome by increasing concentration of substrate • noncompetitive inhibition • impede reactions by binding to another part of the enzyme, thus changing the shape of the active site and making it less effective • **often pesticides, antibiotics, and toxins are inhibitors

9. enzymes need to be told when and where to be active so only necessary reactions are occurring • Allosteric regulation • protein function changed by binding of another molecule • has active (activator binds) and inactive (inhibitor binds) forms • “Chemical on/off switch” • feedback inhibition • end product of reaction binds to enzyme causing inhibition, thus slowing the reaction down