Question

Are enzymes always active?

Answer 1

Enzymes are proteins present in cells that aid in the speeding up of biological reactions. Particular substrates are transformed into specific products by enzymes. The chemical change takes place at the active site of each enzyme. An enzyme must have a highly particular molecular structure in order for the active site to be correctly organised for binding to a substrate and converting it to a product. The substrate will not fit if the active site is misshaped in any manner, and it will stay unchanged.

Complete answer:
Enzymes do not stay active indefinitely.
When enzyme inhibitors attach to the enzyme's active site (competitive inhibitors) or allosteric site (non-competitive inhibitors), the enzyme becomes inactive.
For optimal function, several enzymes require the addition of a coenzyme or enzyme activators.
Apart from inhibitors and activators which affect enzyme activity, there are various other factors like temperature, pH, substrate concentration, product concentration etc which affect enzyme activity by either disrupting their structure or by altering the active sites of the enzymes.
Any change in the three-dimensional structure of enzymes renders them inactive. Heat causes enzymes to become denatured and inactive. In the ideal temperature range, all enzymes are active. In human bodies, the optimum temperature for enzymes is usually approximately $37.5$ degrees Celsius, which is normal body temperature.

Note:
Enzymes reduce the activation energy of a process, which is the amount of energy necessary for it to take place. They accomplish this by attaching themselves to a substrate and keeping it in a position that permits the reaction to proceed more quickly. Enzymes can only function within certain temperature and pH ranges, and poor circumstances can lead them to lose their capacity to bind to a substrate.