Note: Please use the scroll bar to see the entire link.
As seen in Figure 1 in the Structural Background of Ferritin section of the tutorial, peptides combine to form a protein. A peptide is a molecule formed by two or more amino acids. An amino acid (e.g., leucine) is a carboxylic acid (COOH) that also contains an amino group (NH3).
Below is a sketch of three amino acids (Leu-Ala-Glu) that are bound together and form a part of the peptide subunit found in ferritin. The bonds shown in light blue in this sketch are called peptide bonds and each amino acid in the peptide is called a residue. (There are 172 residues in each peptide subunit in ferritin.)
Below are three representations of the peptide subunit in ferritin. The first representation (Figure 1) is a CPK model of the peptide chain. This gives an approximate volume of the subunit. Figures 2 and 3 show ribbon representations of the peptide.
This is a molecular model of the peptide chain that comprises the ferritin protein. It is shown first in the CPK representation and all of the heavy (non-hydrogen) atoms are displayed. CPK pictures represent the atoms as spheres, where the radius of the sphere is equal to the van der Waals radius of the atom.
Note: The carbon atoms are green, the nitrogen atoms are blue, the oxygen atoms are red, and the sulfur atoms are yellow in the CPK model.
Another common representation for proteins and peptides is the ribbon, which traces the backbone of a protein or peptide. This representation does not include the atoms in the sidechains of the residues and is often used to represent the three-dimensional structure. Notice the bundle of helical, or coiled, parts of the backbone. This figure shows a ribbon superimposed on a stick representation that does show the amino-acid sidechains.
This is a ribbon representation of the peptide chain without being superimposed on the stick representation.
Return to Structural-Background Section of Tutorial
Return to Questions on the Background Section of Tutorial
Return to Questions in the Channels Link