Name the protein level by what's bonded to what
- The idea
- Predict
- See it
- Why
- Check
The idea
“A hydrogen bond means secondary, R groups mean tertiary, and a big shape means quaternary.”
It's easy to name the level by the bond type or the shape's size. The same bonds show up at several levels, though.
The short version
The mistake: A hydrogen bond means secondary, R groups mean tertiary, and a big shape means quaternary.
What's actually true: Each level depends on which parts are joined: the sequence, backbone to backbone, R groups in one chain, or chain to chain.
- Primary structure is the amino acid sequence, joined by peptide bonds.
- Secondary structure is helices and sheets, held by backbone hydrogen bonds.
- Tertiary structure is one chain's 3D shape, and quaternary is how separate chains fit together. R group interactions hold both.
On the exam: Backbone to backbone is secondary. R group to R group in one chain is tertiary. Chain to chain is quaternary.