Proteins perform many important functions in living organisms, including movement, immune responses, sensing the environment, energy acquisition, and catalyzing reactions. Proteins are long chains of Amino Acids, and are synthesized by the ribosome, using messenger RNA as a template. There are 20 amino acids commonly found in proteins. contain an , a central carbon atom called the alpha carbon, and a . The 20 amino acids differ by what is attached to the central atom; is variable portion is referred to as the . The amino acid shown is alanine; its side chain is a methyl (-CH3) group.
Proteins are sometimes compared to beads on a string, where each amino acid residue is a bead. These long chins form complicated structures that allow them to perform their function. Even small alterations in any level of the structure can change how the protein does its job, and can lead to diseases.
Levels of Protein Structure
There are four different levels of protein structure. The is the amino acid sequence. The amino acids are connected by an amide bond, made from the amino group (NH2) of one amino acid, and the carboxylic acid (C=O) from another amino acid. The amino acids are linked in a repeating pattern. The backbone of the protein is the repeating N-C-C=O pattern, with the side chains projecting out from the backbone. The end with the free -NH2 group is called the N terminus, while the end with a free carboxylic acid is called the C terminus. The sequence of amino acids is written from the N terminus to the C terminus.
The second level of structure is called secondary structure, and is the shape formed by short sequences of amino acids. This level of structure is stabilized by along the .
For a more in depth discussion of protein structure, see Introduction to protein structure
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