Ina protein there are For levels of structure: Primary, Secondary, Tertiary, and the more complicated Quaternary Structure. Essentially the primary structure of a protein all just the covalent interaction that are present.
The supersecondary structure refers to the combined alpha - helix, and the ß - pleated sheets present. This structure arises when the polypeptide unit folds back on itself in different regions. Representation of a secondary structure:
This is a secondary structure of the enzyme triseptophosphate isomerase. Alpha - helices are seen in red, and ß - sheets in blue, and the connecting loops are in pink.
Another example that describes secondary structure is the enzyme Chorismate Mutase, which is the enzyme I have worked on. ( Modeling of enzyme-substrate binding at the active site).
Again, the helices are in pink, sheets in yellow, and the ß - turns in blue of this secondary structure, which I have imported from Rasmol®, a molecular modeling program.
Tertiary Structures arise from the spatial arrangement of amino acid residues that are represented in a linear sequence near to one another, and its 3-D shape is a balance of attractive and repulsive interactions. An example of tertiary structures are globular proteins, here is a simple structure:
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This is the ribbon model of the enzyme papain. The two parts yellow and blue are known as Domains, and the gap in the middle a Cleft.
Quaternary Structures is the arrangement of subunits and the type of contact made, i.e. it's spatial arrangement, an example could be hemoglobin.
Next topic is Protein Action, where the consequences of protein binding will be discussed.
