Proteins and Enzymes

Objective: Connect amino acid sequence to protein shape.

Proteins are polymers of amino acids linked by peptide bonds. The order of amino acids influences folding because side chains interact with one another and with the surrounding environment. Many proteins have several levels of structure and may contain multiple chains. A protein’s shape helps determine its function, but proteins are dynamic molecules and a single diagram captures only part of their behavior. A change in sequence or conditions may alter structure, with effects that vary by protein and context.

Objective: Explain catalysis without treating enzymes as reactants consumed.

Enzymes are biological catalysts, usually proteins, that speed reactions by lowering the activation-energy barrier through a suitable reaction pathway. A substrate interacts with an enzyme’s active site, and products can leave while the enzyme is available to catalyze additional cycles. Enzymes do not make energetically impossible reactions favorable and do not change the overall energy difference between reactants and products. Some enzymes require cofactors, and binding can involve shape changes rather than a rigid lock-and-key fit.

Objective: Interpret activity changes and denaturation carefully.

Enzyme activity depends on molecular collisions, substrate availability, and the enzyme’s structure. Each enzyme works within some range of temperature and pH; beyond suitable conditions, activity may decrease, and extreme changes can disrupt structure, sometimes irreversibly. The exact optimum differs among enzymes and organisms. A graph of activity versus temperature or pH must be read with its labels and conditions; a peak shows the best observed value for that experiment, not a universal optimum for all enzymes.