In this video, we're going to discuss protein structure. Proteins have a hierarchy of structure organized into four levels: primary, secondary, tertiary, and quaternary. Notice that each of the four levels of protein structure corresponds with the levels in our text and images. The very first level, the primary structure of protein, can be symbolized with the number one. The primary structure refers specifically to the types of amino acids, their quantity, and their specific sequence in the protein chain. Changing either these types, quantities, or the sequence will alter the primary structure. This level is arguably the most important as it determines and dictates all other levels of protein structure.
If we change the primary structure, we could potentially affect the secondary, tertiary, and quaternary structures as well. In our image, each circle represents an amino acid in the protein chain, all covalently linked together via peptide bonds. The primary structure specifies the types, quantity, and order of amino acids.
The next level is the secondary structure of protein, which involves the formation of either α-helices or β-sheets in the protein backbone. This can be symbolized with the number two. In the example image, the protein chain can fold into an α-helix, a winding staircase-type structure, or a β-sheet, an elongated zigzag structure. Thus, the secondary structure specifically refers to these formations in the protein backbone.
Moving on to the tertiary structure of protein, symbolized by the number three, which is easy to remember because the three reminds you of three-dimensional. The tertiary structure refers to the overall three-dimensional shape of the polypeptide chain. Once the backbone folds into α-helices and β-sheets, the protein chain takes on this overall shape, incorporating both α-helices and β-pleated sheets within this structure. All proteins have primary, secondary, and tertiary structures.
The quaternary structure, symbolized with the number four, occurs when a protein has multiple polypeptide chains that associate to form a single functional protein. An example provided is one protein chain with tertiary structure associating with others to form a quaternary structure. This could be a complex with four separate polypeptide chains forming a functional unit, such as hemoglobin, which is found in our red blood cells and helps transport oxygen to our tissues.
This concludes our brief lesson on protein structure, emphasizing the primary, secondary, tertiary, and quaternary levels. We’ll get some practice applying these concepts as we move forward. I'll see you all in our next video.
