Chemical Reactions and Enzymesppt：化学反应和enzymesppt.ppt

Chemical Reactions All processes of life depend on the ordered flow of energy Metabolism – totality of an organism’s chemical processes Metabolic reactions are organized into pathways that are orderly series of ezymatically controlled reactions - two types: Catabolic pathways – rxns that release energy by breaking down complex molecules (ex. Cellular respiration breaks down glucose into CO2 and water) Anabolic pathways – rxns that consume energy to build complex molecules (ex. Photosynthesis makes glucose, making macromolecules from monomers) Exergonic reactions – release energy (catabolic or downhill) Endergonic reactions – require input of energy (anabolic or uphill) Exergonic and endergonic rxns are often coupled – an exergonic rxn provides the energy to drive an endergonic rxn Energy carrier molecules such as ATP couple the rxns Chemical rxns require an initial input of energy (activation energy) to get started – usually supplied by kinetic energy (molecules collide and react) Most rxns occur more easily at higher temps Enzymes Spontaneous rxns proceed too slowly to sustain life at body temp Enzymes act as biological catalysts to speed up chemical rxns to solve this problem Catalyst – a molecule that speeds up a rxn by lowering activation energy (catalyst is not used up in the rxn and remains unchanged) Enzymes are substrate specific Enzymes are very specific and catalyze only a specific type of rxn (remember, proteins have a very specific shape allowing them to function) Lock and Key Model – specific shape of the enzyme allows them to bind to specific molecules and catalyze specific rxns Induced Fit Model Enzyme activity is affected by a cell’s physical and chemical environment Temperature – as temperature increases, enzyme activity increases to a point – extreme temps disrupt hydrogen bonds and ionic bonds holding enzyme’s shape and cause it to denature – most human enzymes have an optimal temp of 35o to 40o C pH – optimal pH range for most enzymes is pH 6 –