Energy and Metabolism (Enzymes) Chapter 6 1

ENERGY LOST With each conversion, there is a one-way flow of a bit of energy back to the environment. Nutrients cycle between producers and consumers. ENERGY GAINED Sunlight energy reaches environments on Earth. Producers of nearly all ecosystems secure some and convert it to stored forms of energy. They and all other organisms convert stored energy to forms that can drive cellular work. ENERGY LOST Energy continually flows from the sun. producers consumers NUTRIENT CYCLING Fig. 6-4, p.74

Laws of Thermodynamics First Law of Thermodynamics –Energy cannot be created or destroyed it can only change from one form to another Second law of thermodynamics –“Energy flows from higher energy, less stable forms to a lower energy, more stable forms” 3

Second Law of Thermodynamics “entropy increases”

Fig. 6-6b, p.96 adenine ribose AMP ADP ATP PPP ATP/ADP Cycle three phosphate groups base sugar

ReactionTypes glucose, a high energy product low energy starting substances + 6O ENERGY IN 6 6 glucose, a high energy starting substance ENERGY OUT low energy products O 2 Endergonic Reaction Exergonic Reaction

The Role of ATP Cells “earn” ATP in exergonic reactions Cells “spend” ATP in endergonic reactions

reactants energy barrier with no enzyme to promote reaction energy barrier with an enzyme’s participation products Activation Energy

Catalysts “Substances that influence chemical bonds in a way that lowers activation energy”. 9

10 Metabolism Total of all chemical reactions carried out by an organism Anabolic reactions / anabolism –Expend energy to build molecules Catabolic reactions/ catabolism –Collect energy by breaking down molecules

11 Enzymes 1. Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster. 2. Reactions do not alter or use up enzyme molecules. 3. The same enzyme usually works for both the forward and reverse reactions. 4. Each type of enzyme recognizes and binds to only certain substrates. Substrate – “the molecule that will undergo the reaction”.

12 How do Enzymes Work?

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Factors Influencing Enzyme Activity Temperature pH

Factors Influencing Enzyme Activity Inhibitors

Allosteric Enzymes allosteric inhibitor allosteric binding site vacant; active site can bind substrate active site altered, can’t bind substrate enzyme active site allosteric activator vacant allosteric binding site active site cannot bind substrate active site altered, can bind substrate Allosteric InhibitorAllosteric Activator

Cofactors

18 Biochemical pathways Reactions occur in a sequence Product of one reaction is the substrate for the next Ex. photosynthesis

Feedback inhibition 19 Pathway with no feedback inhibition Pathway with feedback inhibition