Alpha Helix Protein vs. Alpha DNA? @_@

[Lodgic]

You can hide this advertisement by registering.

I read that an aplha helix in terms of a polypeptide is a structure formed unique in shape by hyrogen bonds being present every 4th peptide bond along the polypeptide chain of amino acids (e.g. in the polypeptide/enzyme lysozyme).

I also read about aplha-DNA (alpha-helix DNA?)...so what is this? Why is it called alpha-DNA? Does it have a similar structure to the alpha helix? Is the alpha-helix just a general term to describe shape?

I hope someone (possibly a uni student ) can answer my questions...otherwise ill have to wait until i start Uni next year for an answer...

thanks

[brenton1987]

An alpha helix is formed by hydrogen bonding between the oxygen in the carboxyl group on one amino acid and the hydrogen in the amino group on a second amino acid. To form the helical structure the amino acids need to be 4 positions apart.

---

William Astbury discovered two different protein structures which he named the alpha form and the beta form. The alpha form was an unstrectched coiled protein while the beta form was produced when the protein was stretched. Although his ideas were wrong his naming system of alpha and beta were kept as the names of the two most common secondary structures for proteins, the alpha helix and the beta pleated sheet. Other much less common secondary structures include the 3₁₀ helix, pi helix, polyproline helix, alpha pleated sheet and the random coil.

---

DNA comes in many different conformations. A-, B-, C-, D-, E-, H-, L-, P- and Z-DNA have all been observed of which only A-, B- and Z-DNA are seen in nature. Both A- and B-DNA are right hand coiled while Z-DNA is left handed.

A-DNA and B-DNA are similar in that they both contain major and minor grooves. A-DNA has more base pairs per rotation which results in it having a deeper major groove and a shallower minor groove. Having more bases per rotation makes A-DNA a more compact molecule that B-DNA. A-DNA is more likely to occur in dehydrated DNA samples.


Z-DNA coils in a zig-zag pattern and forms under specific sequences. Environmental factors which can cause Z-DNA formation include high salt concentrations and DNA supercoiling. The formation of Z-DNA is believed to reduce torsional strain during DNA transcription.