Balance the following equations representing combustion reactions: a. b. (g) ( + + g) (g) (g) (l) ( + + (g) g) (g) H O
Monday, February 22, Class Notes Free energy = the energy available to do work - Marked by G (for Gibbs Free Energy) - G = H - TS - G: usable energy - H: total energy (enthalpy) - S: unusable energy (entropy) Change in free energy: Delta G (reaction) = G (products) — G (reactants) - Positive G = storing energy - Negative G = spontaneous reaction Activation energy = free energy of activation - The energy required for a chemical reaction to start - In biological systems, enzymes lower the energy of attraction - They don’t: - Affect the K - Affect delta G - They do: - Speed up the reactions, without changing thermodynamics - Reduce the amount of energy that it takes to start a chemical reaction Enzymes: “biological catalysts” - Often named “(something)ASE”, i.e. hydrolase, isomerase - Mostly proteins - They interact at the active site, and its shape s all to support that spot - They are unchanged and reusable, which is good because they are expensive to build - Since they are proteins… - Function depends on their shape - The most important thing about an enzyme is its change in shape — shape determines the speciﬁcity of the active site - The exact ﬁt induces activity - Shape change = activity change 8.3 ATP Powers cellular work by coupling exergonic reactions to endergonic reactions. - Cell’s 3 main kinds of work: - Chemical work: pushing of endergonic reactions that would not occur spontaneously, such as the synthesis of polymers from monomers - Transport work: the pumping of spontaneous movement - Mechanical work: i.e. beating of the ulia, contraction of muscle cells, and movement of chromosomes during cellular reproduction - Cells manage their energy with energy coupling: the use of exergonic process to drive an endergonic one - ATP(adenosine triphosphate) - made up of - Sugar ribose - Nitrogenous base adenine - A triphosphate group (chain of 3 phosphate groups) - ATP is used to mediate energy coup;ling and to make RNA - During hydrolysis, terminal phosphate bond is broken by an additional water molecule and it lets out an inorganic phosphate, turning into ADP - When ATP is hydrolyzed it releases energy and becomes surrounded with heat. Proteins harness this energy to perform the 3 kinds of cellular work. - The hydrolysis powers transport and mechanical work — leads to change in protein shape, either directly by phosphorylation or indirectly with nonequivalent binding - ATP is renewable with the addition of phosphate - ATP formation from ADP is not spontaneous — free energy has to be spent - Catabolic pathways (esp. cellular respiration) provide energy - Constant transfer from catabolic to anabolic pathways Friday, February 26 Class Notes Enzymes are inﬂuenced by inhibitors - Inhibitors block the active site - Substrate is competitive so ﬁ you add more it will bring the reaction back up - Sometimes the substrate is not competitive. This happens when the inhibitor changes shape of enzymes - Means we can turn enzymes on and off by changing their shape to regulate them - Allosteric control: turns on, turns off, or stabilizes enzymes - Allosteric means changing shape - Effectors = regulator molecules - Oscilation: going back and forth from bad shape to good shape on its own - Adding an inhibitor keeps it in the bad shape; adding an activator keeps it in a good shape - Cells make positive delta G go - Reaction coupling: attaching exergonic energy to endogonic to make it go - ATP= cellular energy currency - A nucleotide - Used to make DNA (1 of the 4 nucleotides used to make it) Clicker question: Why is ATP considered a “high energy” molecule Answer: It takes less energy to break them than it does to make them.