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3.1 Biological molecules
Quick questions on Proteins: amino acids, peptide bonds and the four levels of structure - AQA A-Level Biology
8short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is primary structure?Show answer
The sequence and number of amino acids in the polypeptide chain, held together by peptide bonds. This is the blueprint for everything that follows.
What is secondary structure?Show answer
The polypeptide folds locally into an alpha-helix or beta-pleated sheet, held by hydrogen bonds between the slightly negative oxygen of one carboxyl group and the slightly positive hydrogen of an amine group along the backbone.
What is tertiary structure?Show answer
The overall 3D shape of a single polypeptide, formed when the chain folds further. It is held by interactions between R groups:
What is quaternary structure?Show answer
Two or more polypeptide chains held together, sometimes with a prosthetic group. Example: haemoglobin has four polypeptide chains, each with an iron-containing haem group.
What are vague "the shape determines function" answers?Show answer
Spell out the chain: sequence → R-group positions → bonds → 3D shape → function.
What is q1?Show answer
Give the general structure of an amino acid and name the bond formed between two of them. [2 marks]
What is q2?Show answer
Explain why the primary structure of a protein is so important. [3 marks]
What is q3?Show answer
Describe the biuret test and state how it would differ for a sample containing protein versus one without. [3 marks]