Two stretches of the polypeptide chain may also adopt a planar structure. In this instance, the hydrogen-bonds responsible for the stability of the structure involve C=O and N-H from non-contiguous aminoacids :
. This is an anti-parallel β-sheet: both aminoacid sequences have opposite orientations(check in which sense the
N-C_α-C=O
block repeats itself in each sequence). Observe how the atoms involved in H-bonding align themselevs in almost straight lines: H-bonds in anti-parallel β-sheets are therefore much stronger tahn those present in parallel β-sheets.

As in parallel β-sheets, the sidechains alternatedly poit upwards ands downwards from the sheet plane. Spin the structure in order to fully appreciate it. See how one of the ends of the sheet contains polar, hydrophylic residues, while the other mostly contains hydrophobic residues (and therefore it probably faces the protein core)

Other interactive models:

Metabolic pathways:

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