Examine the α-helix in Figure 18.1 and determine how many backbone C and N atoms are included in the loop between an amide hydrogen atom and the carbonyl oxygen to which it is hydrogen bonded.

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Hi, everyone. Let's take a look at our next problem. It says true or false. The alpha helix has eight backbone carbon and nitrogen atoms included in a loop between the hydrogen atom of an amid and the carbon oxygen to which it is hydrogen bonded. Use the image of the alpha helix below. And we have an alpha helix drawn here in a condensed structural formula. So we can see our backbone atoms and we can see our hydrogen atom or hydrogen bonds, excuse me in dotted blue lines. So we're supposed to count how many backbone atoms are included in the loop between the two atoms involved in the hydrogen bond. So I'm just going to highlight in yellow are two atoms involved in a hydrogen bond. We'll start at the bottom of the loop from that first amid hydrogen up to the carbon oxygen in the loop above it. And let's count how many backbone atoms we have in between there. So let's get a different color to highlight, we'll do blue and highlight each of our backbone atoms. So starting with the nitrogen that that hydrogen is bound to, we go along to the carbon carbon next to it and then on to a alpha carbon. No, we're going backwards in a sense here, since we are going nitrogen carbon carbon, we are going in the opposite direction. We usually go through a protein chain, we are going from the C terminal because this carbonell would be the C terminal backwards. Just to note there, in case you're confused why we're going nitrogen carbonyl alpha carbon. So again, we have, we've highlighted our alpha carbon. Now we're on to a nitrogen of a previous amino acid there. So we have 1234, five, that's a carbon six, an alpha carbon seven, a nitrogen, eight, a carbon, carbon nine, an alpha carbon 10, a nitrogen, 11, the carbon carbon whose oxygen is involved in the hydrogen bond. So we end up with 11 backbone atoms per loop, those backbones atoms again being comprised of both carbon and nitrogens as we go along there, our question was true or false that the alpha helix has eight backbone carbons. So that is going to be false. And that will be our answer to this question since there are 11 backbone atoms, not eight in that loop of an alpha helix. See you in the next video.

Examine the α-helix in Figure 18.1 and determine how many backbone C and N atoms are included in the loop between an amide hydrogen atom and the carbonyl oxygen to which it is hydrogen bonded.

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Key Concepts

α-helix Structure

Backbone Atoms

Hydrogen Bonding