Question

1) We know that each methylene(-CH2) or methyl (CH3-) grouo in a straight chain hydrocarbon extends the chain lenght by~0.13nm. We also know from stdies of protein strcuture that one turn of an alphaheilx includes 3.6 amino aacid residues and extends the long axis of the helix by ~0.56nm.

A) How long is a sinngle molecule of areachidate in its fully exended form( do not include the carbonyl carbon in your calculation)?

Answer 1

Given the information above, we see that the formula for areachidate or arachidic acid is C₂₀H₄₀O₂

the molecule will look like this:-

0 он CH3 Arachidonic Acid (all-cis-5,8,11,14-eicosatetraenoic acid)

so as we can see, it has 1 CH₃ methyl group and 10 CH₂ methylene groups,

therefore the length of basic straight chain would be

11 x 0.13nm = 1.43 nm

Also, the molecule has one turn which enhances the length by 0.56 nm

so we get 1.43 + 0.56 nm

= 1.99 nm

Note: we have excluded carbonyl carbon from the calculation.