How Do Molecules Interact with One Another?

Molecules in our body, or anywhere else in nature, mingle among one another. And, if things are right, they can interact. When molecules interact the process is called a chemical reaction. For instance, in the reaction below, A and B are substances that react and are called reactants. As a result of this chemical reaction, different substances are produced and are called products. In the chemical reaction below the products are C and D.

In a more realistic reaction, carbon dioxide (CO2) reacts with water to form carbohydrate (C6H12O6) and oxygen (O2). Look familiar? It might, since it is photosynthesis, the process whereby plants make
carbohydrates.
 

The reaction arrow (→) separating the reactants and products merely shows which way the chemical reaction will proceed. A reaction may proceed in only one direction or it may be reversible, whereby the reaction will proceed in either direction. A reversible-reaction arrow looks like you might expect (↔). If there is a number (coefficient) in front of reacting or produced substances this merely tells us how many molecules of a substance must react or be produced in order for the chemical reaction to make sense or to be “balanced.”
 

In chemical reactions, molecules can react to form new molecules

What Is the Design of Molecules?

One limitation of an ink-and-paper representation of molecules is that it often fails to truly capture the three-dimensional beauty of molecules. For example, DNA molecules exist in a spiral staircase design, while many
protein molecules appear to be all bunched (or “globbed”) up. The threedimensional design of a molecule helps determine what that molecule can do (its properties). Furthermore, we will see that many of the important molecules in our body are actually combinations of smaller molecules. For instance, proteins are made from amino acids, and fat molecules are made from fatty acids and glycerol.