Functions of Protein
Now, let's take a quick look at the functions of proteins. There are quite a few different kinds of functions that proteins serve.
There are structural proteins, such as muscle and hair. There are enzymes which control chemical reactions. There are also carrier proteins, such as hemoglobin and myoglobin that carry oxygen through the bloodstream and into the cells. There are also messenger proteins such as hormones, and a number of other different categories of proteins.
Form and Function
The molecular structure of proteins is very important in how the proteins carry out their functions.
Proteins that are structural proteins have to be large. It's also very important that these be insoluble in water, and therefore, the side groups on the amino acids that are used are generally nonpolar side groups.
On the other hand, for things like the enzymes and carriers and antibodies, these in comparison are quite a bit smaller, and in order to facilitate their mobility within the blood and cell fluids, it's necessary that these quite often have polar side groups to allow them to be more soluble.
The tertiary and quaternary structure of the enzymes are very important because that tertiary and quaternary structure must enable the enzyme to grab hold of the specific molecules that it is intended to cause to react. It must hold them in a particular position, and perhaps even transfer some energy to those molecules, to make them react. So the structure or shape of this molecule is very important.
In order for a carrier molecule to carry something like oxygen, it must be able to bond to the oxygen. The antibodies must also be able to seek out and attach to particular kinds of other molecules. Hormones must also have a particular shape in order to activate certain other kinds of molecules. (Not all hormones, by the way, are proteins.)
The Protein - Nucleic Acid Connection
In general then, the function of proteins is to control and facilitate the life processes. That's pretty important. Now, what is it that dictates what proteins exist, and how they are formed?
Let's trace this back. The functions of protein are determined by their composition and their tertiary and quaternary structure. The tertiary structure is determined by the secondary and primary structure. The primary structure involves the amino acids being put together in a certain order.
So, let's go back to this formation of the proteins from the amino acids. How are they put together? What determines the sequence? Let's trace the sequence back to its source.
Proteins are, for the most part, at least they seem to be, manufactured in the ribosomes. They are manufactured in a sequence that is dictated by RNA. RNA is a polymer with a sequence of units. That sequence of RNA units is dictated by a match up with the sequence of units in DNA. DNA is the ultimate genetic chemical. So next, let's look at RNA and DNA, the nucleic acids.