The iceberg that sank Titanic would have been up to a mile long, displacing around a billion tonnes of seawater. It would have taken the iceberg over a year to edge its way down the 40-mile fjord.
Chapters 1 and 2 introduced a-helices and b-sheets (Secondary Struture), and some common motifs composed of 2 or 3 of these elements (Super-secondary Struture). Tertiary structure describes the folding of the polypeptide chain to assemble the different secondary structure elements in a particular arrangement.As helices and sheets are units of secondary structure, so the domain is the unit of tertiary structure.In multi-domain proteins, tertiary structure includes the arrangement of domains relative to each other as well as that of the chain within each domain.There is a blurred distinction between super-secondary structure and tertiary structure.lthough the term motif is often used to describe super-secondary structures (e.g. Branden and Tooze, 1991), it may also be used to describe a consensus sequence of amino acids identified in a number of different proteins, rather than a repeated three-dimensional conformation.
Secondary structure. Definition. noun. A structure of a biological molecule characterized by the local folding within the biopolymer as a result of hydrogen bonding (within the biopolymer). Supplement. In proteins, there are four recognized levels of protein structure: primary structure, secondary structure, tertiary structure, and quaternary structure. A secondary structure of a protein pertains to the folding of a polypeptide chain, resulting in an alpha helix, beta sheet or a random coil structure. Another example of a secondary structure is that of a nucleic acid such as the clover leaf structure of tRNA. See also: protein structure.