Proteins: Primary and Secondary Structure | A-level Biology | OCR, AQA, Edexcel

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The key points covered in this video include:

1. Primary Structure
2. Secondary Structure

Primary Structure of Proteins

Every protein has a unique shape, allowing them all to carry out different functions in organisms. When a polypeptide is made, the order of the amino acids determines the primary structure of the protein. The primary structure of a protein is the sequence of amino acids. Most polypeptide chains are made up of many hundreds of amino acids. There are 20 different naturally occurring amino acids, resulting in trillions of potential combinations. The almost limitless number of combinations allows every protein to have a completely unique primary structure.

Secondary Structure of Proteins

The polypeptide chains formed from joining amino acids together are not always straight. Instead sections of the chain can curl and fold into two main shapes: α- helixes, β-pleated sheets. These shapes arise as due to the structure of amino acids - they all contain a -C=O group and a -NH group when bonded in a chain. The hydrogen in -NH is slightly positive and the oxygen in -C=O is slightly negative - this results in a hydrogen bond between amino acids. In an α- helix, the polypeptide chain coils with hydrogen bonds keeping the coil stable. In β-pleated sheets, the chains form a zig-zag and fold over themselves. Although hydrogen bonds are weak, the many hundreds of them keep the secondary structure stable. The secondary structure of a protein is the curling or folding of the polypeptide chain into α- helices and β-pleated sheets due to the formation of hydrogen bonds.

Видео Proteins: Primary and Secondary Structure | A-level Biology | OCR, AQA, Edexcel канала SnapRevise