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

Revise

• Structure of amino acid• Formation of a peptide bond

C Camino group

carboxylic acid group

R group is different in different amino acids)

Amino Acid Structure text p.26

Peptide bonds and dipeptides

Peptides

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

• Text p.26

The structure of proteins

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

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

Sulphur-containing amino acid Active site

The tertiary structure of an enzyme

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

Globular

protein

3˚

Metabolic

eg. Enzymes, hormones

Fibrous protein

eg. Keratin (hair), collagen (tendons).

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

Protein structure

3.1.2 Protein structure

The relationship between primary, secondary, tertiary and

quaternary structure to function in proteins

A student model

Use a highlighter to show what is ON YOUR SYLLABUS (get it out!)