Lesson 9 of 14 · 5 min
Structure of proteins
NCERT §9.7
Farah cracks an egg into a hot pan and watches the clear white turn solid and opaque. Kabir says she has just wrecked the proteins' shape, and to understand what that means she needs four levels.
The lesson in notes
In short
Biologists describe protein structure at four levels.
Primary structure is the sequence of amino acids, the positional information of which comes first, second and so on. The chain is pictured as a line whose left end is the first amino acid, the N-terminal, and whose right end is the last, the C-terminal.
A protein thread is not a stiff rod. Parts of it coil into a helix, like a spiral staircase, and only right-handed helices are seen in proteins. Other parts fold in other ways. This is the secondary structure.
The long chain also folds back on itself like a hollow woollen ball. This is the tertiary structure, the three-dimensional view of a protein, and it is essential for many of a protein's biological activities.
Some proteins are built from several polypeptide chains, called subunits. How these folded subunits sit relative to one another is the quaternary structure.
Adult human haemoglobin has 4 subunits: two identical alpha subunits and two identical beta subunits.
Watch a class
Prefer a video? Watch this
Four levels of protein structure
The Organic Chemistry Tutor · English · Lecture · Open on YouTube