text: user12686: We are working on an algorithm to assign proteins only on the basis of alpha-carbons.
  My teacher told me to draw a diagram to represent hydrogen bonds only on the basis of alpha-carbons.
  I showed him the following picture:
  
  He said this picture doesn't count, as this diagram shows all the atoms.
  I couldn't figure out how to do this without showing oxygen, non-alpha-carbon, and nitrogen atoms.
  How can I draw a diagram of hydrogen bonds only on the basis of C-alpha backbone?
  
  user6322: There are three options:
  
  it's a badly phrased Ramachandran plot question
  it's a question aimed at the describing the properties of different SS
  it's a trick question
  
  φ & ψ can be used to classify SS (cf. Ramachandran plot), these are however proper dihedrals, so require 4 atoms, which you lack.
  The sequential Cαs in a strand are increasingly distant by 3–4Å, while in a helix there's a periodicity every 3–4 residues. The images you were given are likely to remind you that between two strands in a sheet the Cαs are ~5Å away from the other strand, but the order is different —the indices will increase together in parallel strands, but not in anti-parallel strands.
  A C-alpha trace has the issue that the residues are often not known (UNK is technically represented as homoalanine, but is an unknown) and the resolution is > 4Å. Any SS allocation will be highly inaccurate making it a trick question.
  
original_text: 12686: <p>We are working on an algorithm to assign proteins only on the basis of alpha-carbons.</p>
  <p>My teacher told me to draw a diagram to represent hydrogen bonds only on the basis of alpha-carbons.</p>
  <p>I showed him the following picture:</p>
  <p><a href="https://i.stack.imgur.com/bHeUA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bHeUA.png" alt="enter image description here" /></a></p>
  <p>He said this picture doesn't count, as this diagram shows all the atoms.</p>
  <p>I couldn't figure out how to do this without showing oxygen, non-alpha-carbon, and nitrogen atoms.</p>
  <p>How can I draw a diagram of hydrogen bonds only on the basis of C-alpha backbone?</p>
   6322: <p>There are three options:</p>
  <ol>
  <li>it's a badly phrased Ramachandran plot question</li>
  <li>it's a question aimed at the describing the properties of different SS</li>
  <li>it's a trick question</li>
  </ol>
  <p>φ &amp; ψ can be used to classify SS (cf. Ramachandran plot), these are however proper dihedrals, so require 4 atoms, which you lack.</p>
  <p>The sequential Cαs in a strand are increasingly distant by 3–4Å, while in a helix there's a periodicity every 3–4 residues. The images you were given are likely to remind you that between two strands in a sheet the Cαs are ~5Å away from the other strand, but the order is different —the indices will increase together in parallel strands, but not in anti-parallel strands.</p>
  <p>A C-alpha trace has the issue that the residues are often not known (<code>UNK</code> is technically represented as homoalanine, but is an unknown) and the resolution is &gt; 4Å. Any SS allocation will be highly inaccurate making it a trick question.</p>
  