MPSC Notes - Enzyme Activity Parts - II

11. What happens to a denatured enzyme regarding its functionality? How can that result be explained with the help of the lock and key model?

According to the lock and key model the enzyme functionality depends entirely on the integrity of the activation center, a molecular region with specific spatial characteristics. After the denaturation the spatial conformation of the protein is modified, the activation center is destroyed and the enzyme loses its catalytic activity.

12. What are the main factors that alter the speed of enzymatic reactions?

The main factors that change the speed of enzymatic reactions are temperature, pH and substrate concentration (quantity).

13. How does the substrate concentration affect the speed of enzymatic reactions?

Initially as substrate concentration increases, the speed of the reaction increases; this happens because free activation centers of the enzyme bind to free substrates. Once all activation centers of the available enzymes become bound to their substrates new increments of the substrate concentration will have no effect on the speed of the reaction.

14. How does temperature affect the action of enzymes upon their substrates?

There are defined temperature ranges under which enzymes operate and there is a specific temperature level (optimum temperature) in which enzymes have maximum efficiency. Therefore temperature variations affect enzymatic activity and the speed of the reactions they catalyze.

In addition, as proteins, enzymes can be denatured under extreme temperatures.

15. Concerning enzymatic reactions, how different are the graphic curve of the variation of the speed of a reaction as function of substrate concentration and the curve of variation of the speed of a reaction as function of temperature?

The curve of variation of speed of the enzymatic reaction as a function of growing substrate concentration is a growing curve until the point where it stabilizes due to the saturation of the activation centers of the enzymes.

The curve of variation of speed of the enzymatic reaction as a function of growing temperature has a crescent portion and reaches a peak (the optimum temperature) then it decreases and reaches zero in the point of inactivity of the enzymes by denaturation.

16. How is the cooling of organs and tissues for medical transplants associated with the effect of temperature upon enzymatic reactions?

The molecular degradation during the decomposition of organs and tissues is catalyzed by enzymes. The cooling to adequate temperatures of some organs and tissues destined for transplantation reduces that enzyme activity and thus lessens the natural decomposition process. By the same rationale, the cooling reduces the metabolic work of cells and prevents degradation of their own structures to obtain energy. Elevation of temperature later reverts denaturation of enzymes and the organs and tissues also preserved by other specific techniques may be grafted into the receptors.

17. Does pH affect the enzyme activity?

The concentration of hydrogen ions in solution affects the enzyme activity. Each enzyme has maximal efficiency under an optimum pH.

Since pH is one of the factors for the denaturation of proteins, if an enzyme is submitted to a pH level under which it is denatured there will be no enzymatic activity.

18. Do enzymes act better under acid or basic pH?

Most enzymes act in pH between 6 and 8, a range that corresponds to the general acidic level of cells and blood. There are enzymes, however, that act only under very acid or very basic pH. So enzyme activity depends on pH interval.

In the stomach, for example, the gastric juice has a very low pH, around 2, and there the enzyme pepsin acts to intensively digest proteins. In the duodenum, pancreatic secretions increase the pH of the enteric juice for the action of other digestive enzymes, for example, trypsin.

19. Since pepsin is a gastric enzyme does it have an acid or basic optimum pH? What happens to pepsin when it passes into the duodenum?

Pepsin acts within the stomach so its optimum pH is around 2, an acid pH. When the enzyme passes into the duodenum it meets a higher pH and its enzyme activity ends.

20. What are enzyme cofactors?

Some enzymes need other associated molecules to work. These molecules are called enzyme cofactors and they can be, for example, organic ions like mineral salts, or organic molecules.

Inactive enzymes which are not bound to their cofactors are called apoenzymes. Active enzymes bound to their cofactors are called holoenzymes.

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