Primary (1o) Protein Structure
Proteins are made up of chains of amino acids (50 to >30,000) linked together by peptide bonds.
This is referred to as a polypeptide chain.
"Peptide bond 01" by OpenStax College licensed by CC BY 3.0
Peptide bonds are formed through a condensation/ dehydration chemical reaction.
Secondary (2o) Protein Structure
Secondary protein structure arises when hydrogen bonds form between the amino (N-H) and carboxyl (C=O) groups of the polypeptide backbone.
There are two main types of secondary structure: alpha helices and beta sheets
"Alpha beta structure" by Thomas Shafee licensed by CC BY 4.0
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Alpha helix: has 3.6 amino acids per turn.
(Note: Proline causes an alpha helix to bend, creating kinks, because it cannot form a stabilizing hydrogen bond)
Beta sheet: can be parallel or anti-parallel (as shown in picture above)
What would happen if there was a point mutation in an internal alpha-helix of a multi-subunit protein, causing it to unwind?
a) Nothing would happen to the primary structure
b) Nothing would happen to the tertiary structure
c) The other subunits will unwind
d) a & b
e) a & c
f) None of the above
f) the primary structure will be different due to the amino acid change, and the tertiary structure around the affected helix will change. Though the multiple subunits may separate they will not be unwind because of the faulty helix.