Chapter 5 Enzymes

Question 1

What are catalysts? What is the difference between inorganic vs organic catalyst?

Answer 1

Catalysts are substances that alter or speed up a chemical reaction, without itself being chemical changed at the end of the reaction.

Inorganic vs. organic catalyst: inorganic catalysts are not destroyed by boiling or changes in pH of a solution.

Question 2

What are enzymes?

Answer 2

proteins that function as biological catalysts that alter or speed up chemical reactions, but remain chemically unchanged at the end of a reaction.

Question 3

What are the properties of enzymes

Answer 3

1. Speed up reactions → Enzymes lower activation energy (energy needed to start a chemical reaction) to speed up the rate of reactions that facilitate the conversion of substrates to products. [these are two]
2. Required only in minute (small) amounts → As enzymes remain chemically unchanged at the end of a reaction, only a small amount is needed to catalyse a reaction as they can be reused with many molecules.
3. Substrate-specific → Each reaction in a cell needs a certain enzyme, as different types contain different active sites which determines which substrates they can bind to.
4. Classification → Enzymes are named after the substrate that they act on, followed by an “ase”.
5. Have optimum pH and temperature

Question 4

Explain lock-and-key hypothesis.

Answer 4

Enzyme reactions depend on the presence of specific active sites, which are depressions/pockets on the enzyme’s surface that have a specific shape that the substrate can fit into (like a lock and key – only a specific key can open the lock).

When a substrate fits into an enzyme, it forms an enzyme-substrate complex, and a chemical reaction occurs where the substance is converted into its products (by stressing/weakening chemical bonds). The product then leaves the active site, while the enzyme remains unchanged.

Question 5

Define denaturation. What are the effects of pH and temperature?

Answer 5

Denaturation is the change in three-dimensional structure of an enzyme. This leads to a loss of function.

The loss of function occurs because the change in three-dimensional structure causes the active site to be lost, meaning no substrate can lock onto the enzyme.
This happens when pH is not optimal or temperature is too high.

Question 6

Define limiting factors and explain.

Answer 6

Substrate concentration: Increase in substrate concentration → higher chance of collisions between substrate and enzyme active site → more E-S complex formed → higher rate of reaction
Enzyme concentration: Increase in enzyme concentration → more active sites to bind to substrate → more E-S complex formed → higher rate of reaction