Parallel ?-sheet Explain why ?-sheets are considered \"pleated\" based on what y
ID: 275742 • Letter: P
Question
Parallel ?-sheet
Explain why ?-sheets are considered "pleated" based on what you see in the structure. What is the spacial relationship of the side chains of the amino acids to the sheet? Is there a pattern? Looking at the sheet from the top (or bottom), how would you describe/classify the H-bond pattern between the two sheets?
Anti-Parallel ?-sheet
Looking at the structures, describe how the names anti-parallel and parallel ?-sheets were established Is there much structural difference between the two sheets overall? Looking at the sheet from the top (or bottom), how would you describe/classify the H-bond pattern between the two sheets in the anti-parallel ?-sheet?
Explanation / Answer
?-sheets are considered as extended form of peptide chain. However, they have twists in their arrangement. Hence, they are called pleated sheets.
In a parallel ?-sheet, two peptide chains run in same direction (N- to C-terminus). The hydrogen bonds are formed between the polypeptide backbone N-H and carbonyl groups of adjacent strands. These interchain hydrogen bonds stabilize the ?-pleated sheets.
Anti-parallel ?-sheets run in opposite directions, i.e, one chain runs in N- to C- direction while the other runs in C- to N- direction. The arrangement of hydrogen bonds is different in both parallel and anti-parallel strands.
In an antiparallel ?-sheet, the hydrogen bonds form between adjacent atoms from both the peptide chains, whereas, the hydrogen bonds in parallel sheet look a bit zig-zag. However, in both the cases, hydrogen bonds are fomed in between carbonyl and NH-groups.
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