Protein Srtuctures

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Primary Structure

  • Each protein has a specific function within an organism
  • Each one is formed from amino acids joined by peptide bonds
  • All proteins have an amino group at one end and an acid group at the other
  • The function of the protein is determined by its structure 
  • The structure of each protein is determined by it's amino acid sequence
  • The unique amino acid sequence of a protien or polypeptide is called its primary structure

Different amino acids have different properties. THis means that the sequence of amino acids found in a protein will have an effect on its properties. For example, if the protein contains a number of amino acids with hydrophobic R-groups, then the final protein will be a particular shape and may be found embedded in a membrane.

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The protein's secondary structure is formed when the chain of amino acids coils or folds to form an alpha helix or a  beta pleated sheet. 

Hydrogen bonds hold the coils in place. ALthough they are quite weak, many are formed, so overall they give great stability to parts of the protein molecule. 

An α-helix has 36 amino acids per 10 turns of the coil. H-bonds form between one amino acid and the one 'four places' along the chain. 

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Secondary Structure

The protein's secondary structure is formed when the chain of amino acids coils or folds to form an alpha helix or a  beta pleated sheet. 

Hydrogen bonds hold the coils in place. ALthough they are quite weak, many are formed, so overall they give great stability to parts of the protein molecule. 

An α-helix has 36 amino acids per 10 turns of the coil. H-bonds form between one amino acid and the one 'four places' along the chain. 

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Tertiary Structure

The final three-dimensional shape of a protein is formed when these coils and pleats themselves coil or fold, often with straight runs of amino acids in between.This 3D shape is held in place by a number of different types of bonds and interactions. 

A proteins tertiary structure is vital to its function. For example:

  • hormone must be specific shape in order to fit into the hormone receptor of a target cell.
  •  An enzyme must have an active site, the shape of which is complementary to that of it's substrate. 
  • A structural protein such as collagen, is shaped to be strong with protein chains wound around each other in a specific way.

Heating a protein increases the kinetic energy in the molecule. This causes the molecule to vibrate and breaks some of the bonds holding the tertiary structure in place. This process is called denaturation as the whole tertiary structure can unravel and the protein will no longer function. 

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