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Homework for next week
• Green q 1,2,3 p29
• Do evaluation points from Biuret Practical
• Revise test on all work next week• Bring evidence you have revised
please
3.1.2 Protein structure
The relationship between primary, secondary, tertiary and
quaternary structure to function in proteins
C Camino group
carboxylic acid group
R group is different in different amino acids)
Amino Acid Structure text p.26
PolypeptidesWhen more amino acids are added to a dipeptide, a polypeptide chain is formed.
A protein consists of one or more polypeptide chains folded into a highly specific 3D shape.
There are up to four levels of structure in a protein: primary, secondary, tertiary and quaternary. Each of these play an important role in the overall structure and function of the protein.
Protein structure cont.. Secondary structure
• Hydrogen Bonds occur between the NH and C=O of the peptide bond, between different amino acids in the chain
• 1 hydrogen bond is weak • The chain coils up into a helix shape (called
ALPHA HELIX)• (Beta pleated sheet is a different shape of
secondary structure – again held by H bonds)• Protein may have none, just alpha helix, just
beta pleated sheet or both forms of secondary structure
Alpha helix Beta pleated sheet
Tertiary structure• Further folding to give a complex
3d shape known as tertiary structure
• Shape is called GLOBULAR• Depends on the a.a. sequence• 3 types of bonds holding tertiary
structure in place:• 1 disulphide bonds – strong
(between S in adjacent ‘R’ groups)• 2 ionic between carboxyl and
amino groups not involved in peptide bonds. Weaker than covalent, broken by extremes of pH
• 3 hydrogen bonds -numerous, weak
animation
Quaternary structure• 2 or more
polypeptide chains joined together
• Same types of bond hold it as tertiary structure (all 3)
• There can be non-protein (prosthetic) groups e.g. haem group containing iron
• E.g. haemoglobin
Haemoglobin Molecule
iron-containinghaem group
beta chain beta chain
alpha chain alpha chain
Levels of protein structure
Level Description Bonds Between groups
Primary 1o Sequence of amino acids
Peptide Amino and carboxylic acid
Secondary 2o Alpha helixBeta sheet
Hydrogen bonds C=O and N-H
Tertiary 3o FoldingGlobular shape
Disulphide(Ionic)(Hydrogen)
Amino acids with sulphur in
Quaternary 4o More than 1 polypeptide joined together
As tertiary As tertiary
3.1.2 Protein structure
The relationship between primary, secondary, tertiary and
quaternary structure to function in proteins
A student model