Proteins What do we need proteins for? What foods are good protein sources? How do we test for the presence of proteins?

Primary structure The sequence of amino acids that forms the protein Determined by the order of bases in DNA Position and proportion of amino acids can vary

Secondary structure Formed when the chain of amino acids coils or folds. Forms either an alpha helix beta pleated sheet. Hydrogen bonds give stability due to quantity.

Heating a protein causes denaturation Tertiary structure 3D shape of a protein Vital to its function Bonds between R groups that stabilise the 3D shape: Disulphide bonds Ionic bonds Hydrogen bonds Hydrophilic and hydrophobic interactions Heating a protein causes denaturation

Quaternary structure Some proteins are made up of more than one polypeptide subunit joined together / or a polypeptide and an inorganic component Examples include haemoglobin (4)and insulin(2) Not all proteins have a quaternary structure

Classification of Proteins Globular Fibrous Soluble Metabolically active (involved in reactions) Rolls up into balls (globules) Eg Enzymes Antibodies Haemoglobin Plasma proteins (mostly α helix) Insoluble Structural Forms fibres Eg Collagen Keratin (mostly β pleating)

Functions of Proteins Actin and Myosin Antibodies Hormones Enzymes (Immunoglobulins) Hormones Enzymes Keratin Haemoglobin Collagen

Haemoglobin (globular, water soluble protein) 4 polypeptide subunits (2 alpha and 2 beta). Shape vital to function – to carry oxygen from lungs to the tissues Most of structure is alpha helix Haem group (prosthetic group), contains Fe2+ and is responsible for the colour Each molecule binds 4 oxygen molecules 4 O₂

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Collagen (Insoluble fibrous protein) 3 polypeptide chains, wound around each other. Each of the three chains are coils, held together with Hydrogen bonds Each collagen molecule forms strong covalent bonds (cross-links) with other collagen molecules. Forms collagen fibrils. Many collagen fibrils together form a collagen fibre.

Why is Collagen so strong? Glycine is small and this allows close packing between molecules Collagen chains form a tight coil….they lie close to each other Many hydrogen bonds between R groups hold 3 chains together very closely Strong covalent bonds with adjacent molecules creating a very stable fibril fibre composed of parallel fibril molecules and the ends of these parallel molecules are staggered which prevents line of weakness

Collagen provides mechanical strength in many areas including.... Walls of arteries Tendons Formation of bones Cartilage and connective tissue Used in cosmetic treatments e.g. Lip plumping

Making polypeptides and proteins On ribosome (protein synthesis) Uses mRNA According to the code on the mRNA the amino acids are assembled in the right order and then joined by a peptide bond.

Breaking down proteins Enzymes involved... Protease enzymes Looking at two examples: Hormone regulation Ageing

Answers

ci. H bonds ii. Globular Made of 2 types of polypeptide Contains a non-protein/prosthetic/Haem group Transport of oxygen

Roles of Proteins

Homework Revision for Biological molecules test on Monday 9th March