CHAPTER 5

INTRODUCTION TO METABOLISME

Learning goals :Define energy and the underlying organization of lifeExplain cellular worksDescribe enzymes structure and functionsExplain factors influencing enzymes activity

The Energy of life :CATABOLIC PATHWAYSRelease energyBreaking down complex molecules to simpler compounds.

ANABOLIC PATHWAYSConsume energyBuild up a complex molecules from simpler elements.

Laws of thermodynamics : I and II .

METABOLISME : an emergent property of life that arises from orderly interactions between molecules.Two metabolic pathways :

Energy Conversion :Exergonic Reaction :Chemical products have less free energy than the reactant molecules.Reaction is energetically downhill.Spontaneous reaction

Endergonic ReactionProducts store more free energy than reactants.Reaction is energetically uphill.Non-spontaneous reaction ( requires energy input)

The energy profile of a reaction

In order to make these molecules reactive when necessary, cells use biological catalysts :Named ENZYMEs which are :ProteinsLower activation energySpeed up reaction without change their natureVery selective for which reaction they will catalyze.

The Mechanism of enzyme reactionLEKeS

Important Terms :Catalyst

EnzymesSubstrate

Active Site

Chemical agent that accelerates a reaction without being permanently changed in the process, so it can be used over and over.Biological catalysts.The substance an enzyme acts on and makes more reactive.Restricted region of an enzyme molecule which binds to the substrate.

Lock and key hypothesisActive site

EEnzymeSSubstrateESEnzyme-substrate complexEEnzymePProduct++

Factors affecting enzyme activity

E. CofactorsA small non protein molecules that are required for proper enzyme catalysis.Some are inorganic (zinc, iron or copper)Some are organic and are called coenzymes (mostly vitamins)They may bind tightly to active site or bind loosely to both active site and substrate.

F. Enzyme Inhibition

G. Allosteric RegulationAllosteric site is a specific receptor site on some part of enzyme molecule other than the active site.Binding of an activator to an allosteric site stabilizes the active conformation.Binding of an inhibitor (noncompetitive) will stabilizes the inactive conformation.Subunits may interact so that a single activator or inhibitor at one allosteric site will affect the active sites of the other subunits.

H. CooperativitySubstrate molecules themselves may enhance enzyme activity. Cooperativity is the phenomenon where substrate binding to the active site of one subunit induces a conformational change that enhances substrate binding at the active sites of the other subunits.

Lipase is used in the ripening of cheese1. Enzyme is not destroyed by the reactions its catalyse 2. Enzyme are highly specific.Lock and key hypothesis