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"Continental Classroom - A Course in Modern Chemistry"

"Continental Classroom - A Course in Modern Chemistry" 1960.
A production of the National Broadcasting Company and the Learning Resources Institute in cooperation with the American Association of Colleges for Teacher Education and the American Chemical Society.

Demonstrating Symmetry. (2:37)


Transcript

Linus Pauling: I mentioned that the amino acids are all left-handed amino acids, except glycine, they don't have any symmetry elements. Now, the residues in the polypeptide chain are very much like one another. They differ only in the side chain of atoms that are attached to the central carbon atom and we might well expect that in a stable structure, each residue would be related to the next one in the same way. The mathematicians have proved and interesting theorem. It is this: If one has an asymmetrical object such as this fish. This is a flounder, a flatfish, its left hand is different from its right, not like ordinary fish that have a median plane of symmetry. If one has an asymmetric object which is related to a second equivalent object by some translation, some general operation in space, and that is related to the third in a certain way, the same way, and that to the fourth in the same way, the automatically there is built up a helix. As this operation is repeated, a helix is generated. Here I have the result of operating on a flatfish to convert it into a second flatfish, also a left-handed flatfish, and then into a third one, a fourth one, and in this way this helix is built up. The most general structure that can be made by the operation on an asymmetric object of the same operation over and over again is a helical structure. Well, this suggests to us that the amino acid residues and the polypeptide chains may be related to one another in a helical fashion. And, if I take this model and just start doing the same thing over and over to successive residues, twisting always in the same direction around and around like that, I get very quickly the structure that is shown here. This is a little helix in which each of the residues is attached to a residue some distance removed from it along the chain by an N-H-O hydrogen bond. This structure, this helical structure, is called the alpha helix and it is a very important structure in proteins. This is the primary way in which peptide chains are folded in proteins.

Clip

Creator: Linus Pauling
Clip ID: 1960v.37-07

Full Work

Creator: Linus Pauling
Associated: John F. Baxter, National Broadcasting Company

Date: 1960
Genre: video
ID: 1960v.37
Copyright: More Information

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