The big idea: Some proteins are more than one folded chain. How the chains fit together is the quaternary structure.
The points to remember
- Quaternary structure: two or more polypeptide chains held together as one protein.
- Insulin: two chains joined by disulfide bonds.
- Collagen: three chains wound together into a triple helix.
- Haemoglobin: four chains, two alpha and two beta.
Remember it as: Insulin 2, collagen 3, haemoglobin 4.
Not every protein has it: A protein made of one chain, like myoglobin, has no quaternary structure: its highest level is tertiary.
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
Start Studying Free Full access to Aimnova Pro · cancel anytime
The big idea: Some proteins need a non-protein partner to work. Haemoglobin cannot carry oxygen without its haem groups.
The points to remember
- A non-conjugated protein is made of polypeptide chains only: insulin, collagen.
- A conjugated protein also has a non-protein part, a prosthetic group.
- Haemoglobin is conjugated: each of its four chains carries a haem group containing iron, which binds oxygen.
- Cryo-electron microscopy freezes molecules and images them, so single proteins can now be seen.
Remember it as: Conjugated = protein + a non-protein part.
Non-conjugated
- Polypeptide chains only
- Insulin: 2 chains
- Collagen: 3 chains
Conjugated
- Chains + a prosthetic group
- Haemoglobin: 4 chains
- + 4 haem groups with iron
Real example: seeing single proteins: Cryo-electron microscopy earned the 2017 Nobel Prize in Chemistry. It has shown the shapes of proteins such as the spike protein of the virus that causes COVID-19.
Feeling unprepared for exams?
Get a clear study plan, practice with real questions, and know exactly where you stand before exam day. No more guessing.
Get Exam Ready FreeYour first topic is free to keep • No credit card required
How it is asked: A three-mark Outline of the structure of haemoglobin, and a Paper 1A conclusion from a diagram of insulin's chains.
IB-style questionOutline[3 marks]
Outline the structure of a haemoglobin molecule.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
And a Paper 1A conclusion from a diagram:
IB-style questionIdentify[1 mark]
A diagram shows insulin as two chains of amino acids linked by S-S bonds. What can be concluded?
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.