Summary
Local folding of the backbone into alpha helices and beta sheets stabilised by hydrogen bonds.
In depth
Alpha helices coil with hydrogen bonds between the C=O of one residue and the N-H four residues ahead; beta sheets form between adjacent strands, parallel or antiparallel. Turns and loops connect them.
Keratin is rich in alpha helices; silk fibroin is mostly beta sheets.
Remember: secondary structure involves backbone hydrogen bonds only, not the R groups.
The alpha helix has 3.6 residues per turn and a pitch of 0.54 nm; the side chains point outward. Beta sheets are pleated and can be very stable, as in silk fibroin and in amyloid fibrils. Proline and glycine often break helices.
Prediction of secondary structure from sequence was an early goal of bioinformatics, and Pauling and Corey proposed the helix and sheet in 1951. Ramachandran plots show which backbone angles are allowed.
Frequently asked questions
What is Secondary Structure?
Local folding of the backbone into alpha helices and beta sheets stabilised by hydrogen bonds.
Which area of biology covers Secondary Structure, and how advanced is it?
Secondary Structure is one of the 51 topics in Biomolecules & Biochemistry. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Amino Acids, Protein Folding and Chaperones, Tertiary Structure.
Can you give an example of Secondary Structure?
Keratin in hair is mostly alpha helix, and perming hair breaks and re-forms disulfide bonds between helices.
What should I learn before Secondary Structure?
Work through the Beginner topics in Biomolecules & Biochemistry first, such as Water Properties, Carbon Chemistry, Carbohydrates, then return to Secondary Structure. Intermediate topics assume the Beginner vocabulary.
What topics are related to Secondary Structure?
The closest topics to Secondary Structure are Amino Acids, Protein Folding and Chaperones, Tertiary Structure, Peptide Bond. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Secondary Structure?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Secondary Structure. To practise the whole of Biomolecules & Biochemistry, use the Biomolecules & Biochemistry quiz.
How is Secondary Structure different from Amino Acids?
Secondary Structure: Local folding of the backbone into alpha helices and beta sheets stabilised by hydrogen bonds. Amino Acids: Twenty building blocks, each with an amino group, a carboxyl group and a variable side chain. Read both side by side and note what each one explains.
How should I study Secondary Structure step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Amino Acids and explain the difference aloud. Finally, take the Biomolecules & Biochemistry quiz and come back to this page for any question you miss.