dr.mum
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When I read Lippincott, Page 24, Q 2.2:
Which one of the following statements is correct?
A.
B.
C. B-Bends ofter contain proline
D. Motifs are a type of secondary structure.
E.
Correct answer is C. I know that. But I can not understand why D is wrong. The explanation by the book is Motifs are elements of tertiary structure.
But in the same book, page 18, it says E Supersecondary structures (motifs). supersecondary structure is not a secondary one?
Thanks.
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| crane
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I think motifs are usually not that simplely formed by secondary structrues. So, supersecondary structrue does not = secondary structrue.
Hopefully, that helps
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| GoodGirl
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Dear dr.mom,
I did not have an answer , so I went online to look for it . And this is what I found ... Hope it will explain your query ......
Historically, the first hierarchical description of protein structure contained two more levels, in addition to primary and secondary (Linderström-Lang and Schellman, 1959). Tertiary structure concerns how the secondary structure units associate within a single polypeptide chain to give a three-dimensional structure. Quaternary structure describes how two or more polypeptide chains associate to form a native protein structure (but some proteins consist of a single chain).
These definitions are still valid, but more detail has since been added to the hierarchy. The introduction of the term "supersecondary structure" was necessary when it became clear that certain arrangements of two or three consecutive secondary structures (alpha-helices or beta-strands), are present in many different protein structures, even with completely different sequences. Classic units of supersecondary structure include the alpha-alpha unit (two antiparallel alpha-helices joined by a 'hairpin' bend changing the chain direction by 180°); the beta-beta unit (two antiparallel strands connected by a hairpin); and the beta-alpha-beta unit (two parallel strands, separated by an alpha-helix antiparallel to them, with 2 hairpins separating the three secondary structures). Sometimes the term 'motif' is used to describe these supersecondary structures. Other motifs of supersecondary structure have been described, such as the alpha-beta-beta and beta-beta-alpha units (Chothia, 1984). Because supersecondary structure involves associations of secondary structures, supersecondary structure may logically be considered to be a subset of tertiary structure (see the definition above). On the other hand some literature may present supersecondary structure as a separate level in its own right. It is important to realize that by no means all helices and strands in proteins belong to supersecondary structures. For example, proteins of the globin family consist of eight alpha-helices in contact; but the helices do not pack against other helices which are adjacent in the sequence, with the exception of the final two, which form an antiparallel helix-turn-helix motif. Again, the three- dimensional formation of these eight helices is the protein's tertiary structure. Some relatively common combinations of the supersecondary structural motifs described above are observed in proteins. For example, there are a considerable number of proteins with a four-helix bundle, consisting of two alpha-alpha units connected by a loop. A common motif is the beta-alpha-beta-alpha-beta unit- alias the Rossman fold (effectively two consecutive beta-alpha-beta units sharing a strand). Arguably such units can be thought of as more complex supersecondary structural motifs. These larger associations are also called (domain) folds. Some folds are considerably larger than the units described in the previous paragraph, consisting of several supersecondary structures, or secondary structures in other contexts. An example of the latter is the globin fold, six of whose helices cannot be described as a recognized supersecondary structure.
More you can find online at http://www.cryst.bbk.ac.uk/PPS2/course/section9/9...
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| dr.mum
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Thanks, girls.
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God granted me the serenity to accept the things I can not change, the courage to change the things I can, and the wisdom to hide the bodies of those people I had to kill.
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