Which of the following ARE NOT a feature commonly observed i

Which of the following ARE NOT a feature commonly observed in a helices or proteins in general? left-handedness one helical turn every - 7 amino acids A hydrogen bond forms between a polar side chain and an aromatic side chain. amino acid side chains are found buried inside the core of the alpha helix. Which of the following IS/ARE a feature(s) commonly observed in beta sheets? antiparallel regions coiled-coil patterns disulfide bonds r(d) parallel regions Draw a 3-strandcd anti-parallel and a parallel beta sheet, using arrows, be sure to draw the protein that connects each strand in the beta-sheet.

Solution

3. Alpha Helix: a. Left-handedness: alpha helix is both right handed and left handed. But right-handed is more common than the left-handed helix. Left handed helix usually occurs with large content of achiral glycine amino acids, and is less common with other amino acids.

b. It has 3.6 amino acid residues per turn, it corresponds to a rotation of 100^o, per residue enabling the side chains to project out of the helical axis at 100^o interval.

c. Hydrogen bond is formed between the N-H group of the amino acid and carbonyl group of the amino acid four residues earlier. This is a repeated structure, i.e. hydrophobic side chains hydrogen bond with acyl groups

d. Non-polar side chains are buried inside the helical structure and the polar side chains are usually exposed in the alpha-helix.

Hence option b is the correct answer.

4. a & d. Beta sheet comprises of parallel strands of protein, which are oriented adjacent to one another, and appear as a sheet. they can be antiparallel or mixed too. one feature with respect to antiparallel is that it gives more stability due to the 90^o angle between, hydrogen bonds.

b. Coiled coil is when 2-7 alpha helices coil together, forming dimers and trimers, and perform cellular functions like gene expression.

c. disulfide bond: beta sheet is usually stabilized by hydrogen bonding between the carbonyl and amino group, and not disulfide bond. alpha helix and beta sheets are secondary structures which predominantly contain hydrogen bonds, disulfide bonds may occur sometimes in cysteine residues but is quite rare.

Hence a and d are the correct options.