1. 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)

2. 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

3. 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

4. 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)

5. 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

6. Induced Fit Model Induced Fit Model – more current model
Each enzyme has a dimple or groove called the active site into which reactant molecules called substrates fit
When substrate enters active site, both substrate and active site change shape – induced fit (amino acids temporarily bond with substrate or electrical charges distort the chemical bonds in substrate – this promotes the reaction to occur)
New product is expelled and enzyme can go on and accept a new set of substrates

7. 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 – 8 Extremes in pH will denature enzymes
Cofactors – many enzymes require nonprotein helpers – some bind to the active site permanently, others bind reversibly along with substrate (inorganic examples: zinc, iron, copper)
Organic cofactors are called coenzymes – most vitamins are coenzymes

8. Enzyme Inhibitors – certain chemicals inhibit the action of enzymes
Competitive inhibitors – inhibitors that resemble the shape of the normal substrate and compete for the active site and block it
Noncompetitive inhibitors – inhibitors that do not directly compete with substrate at active site – bind to another part of enzyme causing it to change shape so active site cannot bind substrate

9. Metabolism can be controlled by regulating the activity of enzymes
Many enzymes are controlled through allosteric regulation – a regulatory molecule binds to an allosteric site on an enzyme (specific receptor site different from active site)
Allosteric enzymes have an active form (shape) and an inactive form
Allosteric activators/inhibitors bind to allosteric site and change the shape of the enzyme to activate or inhibit the enzyme

10. Feedback inhibition – switching off of a metabolic pathway by it’s end-product which acts as an inhibitor of an enzyme within the pathway (often by allosteric inhibition)

11. Industrial Uses of Enzymes
Enzymes have long been used for industrial purposes
Leather tanning – proteases are used to soften hides and remove hair
Brewing – enzymes in barley grains at germination are used to convert stored starch to sugars that can be fermented by yeast
Biotechnology – enzymes are frequently used in genetic engineering
Lactose-free milk – some people are “lactose-intolerant” (do not produce lactase in pancreatic juices) – cannot digest milk and milk products
Lactase is obtained from bacteria
Milk and milk products are treated with lactase before consumption to remove lactose