User:James D Watson/Structural Templates: Difference between revisions
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===β-sheets=== | ===β-sheets=== | ||
<applet load='1vkp' size='350' frame='true' align='right' caption='Secondary structure - Beta'/> | <applet load='1vkp' size='350' frame='true' align='right' caption='Secondary structure - Beta'/> | ||
A single beta-strand can be described as a flat helix with 2 residues per turn although this may not be initially obvious. When two or more beta strands lie next to each other, forming hydrogen bonds between them, this is what is termed a β-sheet. As the backbones need to come close together to interact and form a sheet, the sidechains are oriented away from the plane of the sheet. As the polypeptide chain is synthesised from the amino terminus to the carboxyl terminus it has a directionality (represented in cartoon form as an arrowhead on beta strands). β-sheets therefore occur in two varieties:<OL> | A single beta-strand can technically be described as a flat helix with 2 residues per turn although this may not be initially obvious. When two or more beta strands lie next to each other, forming hydrogen bonds between them, this is what is termed a β-sheet. As the backbones need to come close together to interact and form a sheet, the sidechains are oriented away from the plane of the sheet. As the polypeptide chain is synthesised from the amino terminus to the carboxyl terminus it has a directionality (represented in cartoon form as an arrowhead on beta strands). β-sheets therefore occur in two varieties:<OL> | ||
<LI>Anti-parallel - here the beta strands aligned next to each other run in opposite directions. As the interacting carbonyls and amides align well, the hydrogen bonds appear to be straight. | <LI>Anti-parallel - here the beta strands aligned next to each other run in opposite directions. As the interacting carbonyls and amides align well, the hydrogen bonds appear to be straight. | ||
<LI>Parallel - here the interacting strands run alongside each other and point in the same direction. In this conformation the carbonyl oxygen and the amides tend to be more staggered than in an anti-parallel sheet, therefore the hydrogen bonds tend to be angled. | <LI>Parallel - here the interacting strands run alongside each other and point in the same direction. In this conformation the carbonyl oxygen and the amides tend to be more staggered than in an anti-parallel sheet, therefore the hydrogen bonds tend to be angled. | ||
