11. Generally, antiparallel strands of a 0-sheet are connected via short peptide

Question

11. Generally, antiparallel strands of a 0-sheet are connected via short peptide loops, whereas parallel strands are connected by longer structures such as an -helix. Why do you think this is so? Please access the molecular model of the catabolite activator protein (CAP) involved in regulation of the lac operon in bacteria at the following web address (https://media.pearsoncmg.com/bc/bc Omedia gen/js mol/cap/cap.html; also posted to Blackboard). This activity provides a nice tutorial of the interactions important in both protein structure and protein-DNA interactions.

Explanation / Answer

Generally antiparallel strands of a beta sheet are connected via short peptide loops,
whereas parallel strands are connected by longer structures such as an alpha helix.
In beta hairpin structure, two antiparallel strands are linked by short loop of 2 to 5
residues of glycine or a prolin which take dihedral angle conformation needed for turn or
loop. In alpha helices, usually there will be positively charged residues which in turn
generate loner and narrow loop.

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