Proteins

Assumed Knowledge

• Amino acid structures and properties• Secondary structure (α-helix and β-sheet).• Protein synthesis occurs on ribosomes

(cytoplasm) – covered in the genetics presentation

• Functions of proteins

Amino Acids

Amino acids are the building blocks of proteins

There are 20 amino acids found in proteins

All have a standard structure

Properties• Size – small, bulky, affects the folding of a

protein• Charge • H – bonding• Disulphide bonding between two cysteine

amino acids

Protein Structure

• Primary structure – the sequence of amino acids (the polypeptide chain)

• Secondary structure – folding into an α-helix or a β-sheet

• Tertiary structure – further folding of the protein

• Quaternary structure – association of multiple proteins to form a multi-subunit protein

Peptide bond – bonds between the amino group and the carboxyl groups of amino acids. The bonds form with the loss of water - dehydration reaction

α-helix - right handed coil structure with precise spacing throughout

β-sheet – a lateral connection of β-strands (stretches of amino acids)

Collagen – most abundant protein

Made of three left handed helices arranged in a right-handed super helix

Protein Function

• Enzymes - kinase • Transport - haemoglobin and myoglobin (O2)• Storage - haemoglobin• Motility - actin and myosin.• Structure – collagen• Defence - immunoglobulins (antibodies).• Communication - Signals (insulin) and receptors

(insulin receptor)• Gene control - transcription factors