 Energy – the capacity to perform work  Its types: › Kinetic energy › Potential energy  A form of kinetic energy is heat.  A form of potential energy is chemical energy (energy of molecules)

 Chemical reactions can store or release chemical energy.  If a reaction is endergonic – energy is taken in by the reactants to form the products (like dehydration synthesis or photosynthesis)  If a reaction is exergonic – energy is released by the reactants to form the products (like cellular respiration)  Frequently, exergonic reactions fuel endergonic reactions – energy coupling

 ATP: A modified nucleotide molecule that powers all cellular work directly.  Its structure: adenine, ribose and three phosphates are combined by dehydration synthesis

 ATP molecules release phosphate groups to various other molecules. These molecules take in the phosphate by phosphorylation and get excess energy to perform various processes.  When ATP releases a phosphate + energy it produces ADP (adenosine diphosphate)  ADP can turn back to ATP by taking in a phosphate and energy by phosphorylation

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 The energy from ATP can be used for the following processes: › Chemical work (forming products from reactants) › Mechanical work (contracting muscle) › Transport work (moving substances into or out of the cell)

 Enzymes are proteins that act as biological catalysts in living organisms.  They speed up chemical reactions by lowering the activation energy of the reaction.  wf wf

 Enzymes have a specific section called the active site that is able to bind with the reactants ( substrates ) of a chemical reaction  Once the substrates bind to the active site, the active site changes shape and pulls the reactants together. As a result, the reaction occurs faster and more efficiently.  The model that describes that enzymes change shape when bind with the substrate is called the induced fit model

 Animations: hill.com/sites/ /student_view0/chapter2/animation __how_enzymes_work.htmlhttp://highered.mcgraw- hill.com/sites/ /student_view0/chapter2/animation __how_enzymes_work.html  Enzyme%20activity.html Enzyme%20activity.html  ons/enzyme.swf ons/enzyme.swf

 Three important special characteristics of enzymes: › They are specific › They are efficient › They are sensitive

 Many enzyme do not function without an additional group attached to them. This additional group is called a cofactor.

 Some substances can stop enzymes from functioning by attaching themselves to the active site of the enzyme. These are called inhibitors.  Many inhibitors are used as poisons or drugs.