Question

Please help me understand the following questions by providing me with some explanation.

- What are enzymes and how do they work?

- How are they different from inorganic catalysts?

- Explain and draw reaction coordinate diagrams. (Free energy vs. reaction progress)

- Exergonic vs. endergonic reactions.

Answer 1

Enzymes are biological molecules (typically proteins) that significantly speed up the rate of virtually all of the chemical reactions that take place within cells.

Some enzymes help break large molecules into smaller pieces that are more easily absorbed by the body. Other enzymes help bind two molecules together to produce a new molecule. Enzymes are highly selective catalysts, meaning that each enzyme only speeds up a specific reaction.

The molecules that an enzyme works with are called substrates. The substrates bind to a region on the enzyme called the active site.

There are two theories explaining the enzyme-substrate interaction.

In the lock-and-key model, the active site of an enzyme is precisely shaped to hold specific substrates. In the induced-fit model, the active site and substrate don't fit perfectly together; instead, they both alter their shape to connect.

Let us consider the diagram at left to represent an elementary reaction that can take place with or without catalysis. The red curve shows the energy profile for the uncatalyzed reaction. The activation energy for uncatalyzed conversion to products is much greater than that for the catalyzed reaction (indigo curve). This means that the rate constant for the catalyzed reaction, kcat, will be much greater than kuncat, the rate constant for the uncatalyzed reaction. For both the uncatalyzed and the catalyzed reaction, the potential energy change, ΔErxn, is the same. This means that while a catalyst does not alter the conditions under which the reaction is at equilibrium, it greatly speeds up the approach to equilibrium. The reaction coordinate diagram shows that the energy of activation for the reverse reaction is lowered by the catalyst as well.

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