Enzymes and metabolic pathways

All metabolic processes depend on reaction between molecules, with breaking of some covalent bonds and the formation of others, yielding compounds that are different from the starting materials. In order to understand nutrition and metabolism it is therefore essential to understand how chemical reactions occur, how they are catalysed by enzymes and how enzyme activity can be regulated and controlled.

After reading this chapter you should be able to:

  • explain how covalent bonds are broken and formed, what is meant by thermoneutral, endothermic and exothermic reactions and how reactions come to equilibrium;
  • explain how a catalyst increases the rate at which a reaction comes to equilibrium and how enzymes act as catalysts;
  • explain how an enzyme exhibits specificity for both the substrates bound and the reaction catalysed;
  • define a unit of enzyme activity;
  • explain how pH, temperature and concentration of enzyme affect the rate of reaction;

describe and explain the dependence of the rate of reaction on concentration of substrate, define the kinetic parameters K and V and explain how they are

determined experimentally;

explain how enzymes may show cooperative binding of substrate and how this affects the substrate dependence of activity;

describe the difference between irreversible and reversible inhibitors of enzymes, their clinical relevance and how they may be distinguished experimentally; describe the difference between competitive and non-competitive reversible inhibitors of enzymes, their clinical relevance and how they may be distinguished experimentally;

explain what is meant by the terms coenzyme and prosthetic group, apoenzyme and holoenzyme and describe the roles of coenzymes in oxidation and reduction reactions;

describe the classification of enzymes on the basis of the reaction catalysed; describe and explain what is meant by a metabolic pathway and by linear, branched, spiral (looped) and cyclic pathways.

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