1) If W is the first residue, and there are 18 residues in total, how many amino

Question

1) If W is the first residue, and there are 18 residues in total, how many amino acids are there? How many full turns does the helix make?

(Would the answer be 18 amino acids, and 5 turns? )

2) What percent of the helix is likely to be in direct contact with the membrane?

(Since I,V,A,L are hydrophobic and the rest are either charged or polar, and only polar amino acids would direct the membrane, would the answer be 13/18 = 72.2% ? )

1) If W is the first residue, and there are 18 residues in total, how many amino acids are there? How many full turns does the helix make? (Would the answer be 18 amino acids, and 5 turns? ) 2) What percent of the helix is likely to be in direct contact with the membrane? (Since I,V,A,L are hydrophobic and the rest are either charged or polar, and only polar amino acids would direct the membrane, would the answer be 13/18 = 72.2% ? )

Explanation / Answer

1. The ?-helix has 3.6 residues per turn so 18 amino acids have 5 turns

2. Hydrophobic amino acid residues build up the core while polar and charged amino acids preferentially cover the surface of the molecule comprises membrane. Therefore after excluding I,V,A,L (hydrophobic) we get 13 polar and charge amino acids which are in contact with membrane

so percentage of helic in contact with membrane is 13/18 = 72.22%

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