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Chemical ReactionsChemical Reactions All processes of life depend on the ordered All processes of life depend on the ordered
flow of energyflow of energy MetabolismMetabolism – totality of an organism’s – totality of an organism’s
chemical processeschemical processes Metabolic reactions are organized into Metabolic reactions are organized into
pathways that are orderly series of pathways that are orderly series of ezymatically controlled reactions - two types:ezymatically controlled reactions - two types:
1.1. Catabolic pathwaysCatabolic pathways – rxns that release energy – rxns that release energy by breaking down complex molecules (ex. by breaking down complex molecules (ex. Cellular respiration breaks down glucose into Cellular respiration breaks down glucose into COCO22 and water) and water)
2.2. Anabolic pathwaysAnabolic pathways – rxns that consume energy – rxns that consume energy to build complex molecules (ex. Photosynthesis to build complex molecules (ex. Photosynthesis makes glucose, making macromolecules from makes glucose, making macromolecules from monomers)monomers)
Exergonic reactions Exergonic reactions – release energy (catabolic or – release energy (catabolic or downhill)downhill)
Endergonic reactionsEndergonic reactions – require input of energy (anabolic or – require input of energy (anabolic or uphill)uphill)
Exergonic and endergonic rxns are often Exergonic and endergonic rxns are often coupledcoupled – an – an exergonic rxn provides the energy to drive an endergonic exergonic rxn provides the energy to drive an endergonic rxnrxn
Energy carrier molecules such as ATP couple the rxnsEnergy carrier molecules such as ATP couple the rxns
Chemical rxns require an initial input of energy Chemical rxns require an initial input of energy ((activation energyactivation energy) to get started – usually ) to get started – usually supplied by kinetic energy (molecules collide supplied by kinetic energy (molecules collide and react)and react)
Most rxns occur more easily at higher tempsMost rxns occur more easily at higher temps
EnzymesEnzymes Spontaneous rxns proceed too slowly to sustain life at Spontaneous rxns proceed too slowly to sustain life at
body tempbody temp Enzymes act as biological catalysts to speed up Enzymes act as biological catalysts to speed up
chemical rxns to solve this problemchemical rxns to solve this problem CatalystCatalyst – a molecule that speeds up a rxn by lowering – a molecule that speeds up a rxn by lowering
activation energy (catalyst is not used up in the rxn and activation energy (catalyst is not used up in the rxn and remains unchanged)remains unchanged)
Enzymes are substrate specificEnzymes are substrate specific Enzymes are very specific and catalyze only a specific Enzymes are very specific and catalyze only a specific
type of rxn (remember, proteins have a very specific type of rxn (remember, proteins have a very specific shape allowing them to function)shape allowing them to function)
Lock and Key Model – specific shape of the enzyme Lock and Key Model – specific shape of the enzyme allows them to bind to specific molecules and catalyze allows them to bind to specific molecules and catalyze specific rxnsspecific rxns
Induced Fit ModelInduced Fit Model
When substrate enters active When substrate enters active site, both substrate and active site, both substrate and active site change shape – site change shape – induced induced fitfit (amino acids temporarily (amino acids temporarily bond with substrate or bond with substrate or electrical charges distort the electrical charges distort the chemical bonds in substrate – chemical bonds in substrate – this promotes the reaction to this promotes the reaction to occur)occur)New product is expelled and New product is expelled and enzyme can go on and accept enzyme can go on and accept a new set of substratesa new set of substrates
Induced Fit ModelInduced Fit Model – more current model – more current modelEach enzyme has a dimple or groove called Each enzyme has a dimple or groove called
the the active siteactive site into which reactant molecules into which reactant molecules called called substratessubstrates fit fit
Enzyme activity is affected by a cell’s physical and Enzyme activity is affected by a cell’s physical and chemical environmentchemical environment
1.1. Temperature – as temperature increases, enzyme Temperature – as temperature increases, enzyme activity increases to a point – extreme temps disrupt activity increases to a point – extreme temps disrupt hydrogen bonds and ionic bonds holding enzyme’s hydrogen bonds and ionic bonds holding enzyme’s shape and cause it to shape and cause it to denaturedenature – most human – most human enzymes have an optimal temp of 35enzymes have an optimal temp of 35oo to 40 to 40oo C C
2.2. pH – optimal pH range for most enzymes is pH 6 – 8 pH – optimal pH range for most enzymes is pH 6 – 8 Extremes in pH will denature enzymesExtremes in pH will denature enzymes
3.3. Cofactors – many enzymes require nonprotein Cofactors – many enzymes require nonprotein helpers – some bind to the active site helpers – some bind to the active site permanently, others bind reversibly along with permanently, others bind reversibly along with substrate (inorganic examples: zinc, iron, substrate (inorganic examples: zinc, iron, copper)copper)
• Organic cofactors are called Organic cofactors are called coenzymescoenzymes – most – most vitamins are coenzymesvitamins are coenzymes
4.4. Enzyme Inhibitors – Enzyme Inhibitors – certain chemicals inhibit certain chemicals inhibit the action of enzymesthe action of enzymes
a.a. Competitive inhibitorsCompetitive inhibitors – – inhibitors that resemble the inhibitors that resemble the shape of the normal shape of the normal substrate and compete for substrate and compete for the active site and block itthe active site and block it
b.b. Noncompetitive inhibitorsNoncompetitive inhibitors – – inhibitors that do not inhibitors that do not directly compete with directly compete with substrate at active site – substrate at active site – bind to another part of bind to another part of enzyme causing it to enzyme causing it to change shape so active site change shape so active site cannot bind substratecannot bind substrate
Metabolism can be controlled by regulating the Metabolism can be controlled by regulating the activity of enzymesactivity of enzymes
Many enzymes are controlled through Many enzymes are controlled through allosteric regulationallosteric regulation – a – a regulatory molecule binds to an regulatory molecule binds to an allosteric siteallosteric site on an enzyme on an enzyme (specific receptor site different from active site)(specific receptor site different from active site)
1.1. Allosteric enzymes have an active form (shape) and an Allosteric enzymes have an active form (shape) and an inactive forminactive form
2.2. Allosteric activators/inhibitors bind to allosteric site and change Allosteric activators/inhibitors bind to allosteric site and change the shape of the enzyme to activate or inhibit the enzymethe shape of the enzyme to activate or inhibit the enzyme
Feedback inhibition – switching off of a Feedback inhibition – switching off of a metabolic pathway by it’s end-product metabolic pathway by it’s end-product which acts as an inhibitor of an enzyme which acts as an inhibitor of an enzyme within the pathway (often by allosteric within the pathway (often by allosteric inhibition)inhibition)
Industrial Uses of EnzymesIndustrial Uses of Enzymes Enzymes have long been used for industrial purposesEnzymes have long been used for industrial purposes Leather tanning – proteases are used to soften hids and Leather tanning – proteases are used to soften hids and
remove hairremove hair Brewing – enzymes in barley grains at germination are Brewing – enzymes in barley grains at germination are
used to convert stored starch to sugars that can be used to convert stored starch to sugars that can be fermented by yeastfermented by yeast
Biotechnology – enzymes are frequently used in genetic Biotechnology – enzymes are frequently used in genetic engineeringengineering
Lactose-free milk – some people are “lactose-intolerant” Lactose-free milk – some people are “lactose-intolerant” (do not produce lactase in pancreatic juices) – cannot (do not produce lactase in pancreatic juices) – cannot digest milk and milk productsdigest milk and milk products Lactase is obtained from bacteriaLactase is obtained from bacteria Milk and milk products are treated with lactase before Milk and milk products are treated with lactase before
consumption to remove lactoseconsumption to remove lactose