Proteins, also known as polypeptides, are biomolecules made of the elements carbon, hydrogen, oxygen, and nitrogen. Proteins are essential parts of all organisms and are involved in almost every process within cells.
The monomers of proteins are amino acids. There are 20 different amino acids.
The basic structure of an amino acid is a carbon bonded to hydrogen in the center joined with an amine group, a carboxyl, and a functional group. A generalized structure of an amino acid will show the functional group by using the variable "R." The diagram to the right shows the basic structure of a protein.
There are 20 different functional groups, and they determine the type of amino acid. The 20 amino acids are shown below. The functional groups are shown in blue text.
Source: Twenty amino acids, Biology Online
Like all biomolecules, amino acids combine through dehydration synthesis. When two amino acids join, a water molecule is removed and a special type of bond called a peptide bond is formed. This is why proteins are referred to as polypeptides.
Click on the button that says bond to see the two generic amino acids join.
Proteins are “built” during the cellular process called protein synthesis. There are two main steps in protein synthesis: transcription and translation.
Source: Primary Protein Structure, Wikimedia Commons
The order or sequence in which the amino acids join determines the primary structure of a protein.
Proteins are not long straight molecules, but are usually folded into a 3-dimensional shape. Depending on the protein, the molecule could have as many as 100 amino acids joined together or even several thousand!
Source: Structure of p11 protein, Wikimedia Commons
Sometimes you will see computer-generated images of proteins, as shown in the figure to the left. These are usually referred to as the crystallographic model of a protein. They show the 3-dimensional shape of the protein.
Proteins have numerous functions. Click on the images below to learn about the various functions of proteins.
3. What are some of the functions of proteins?
