Polypeptides (proteins) Flashcards
Features of the amino acid
Carboxylic group (-COOH)
Amine group (-NH2)
One of 20 different R groups
Many amino acid (monomers) can be bonded together to form a polypeptide (polymer).
The formation of a dipeptide
A condensation between the COOH group of one amino acid and the NH2 group of another.
A water molecule is released forming a peptide bond.
Four types of amino acid R groups
Ionic (+ or -)
Cysteine (-S)
Hydrogen bonding (-OH)
Hydrophobic (-CH3)
Detail the 4 levels of protein (polypeptide) folding
Primary structure- the sequence/ order of amino acids in a polypeptide chain.
Secondary structure- localised folding forming alpha helix/ beta pleated sheet, stabilised by hydrogen bonding between the peptide bonds in the chain.
Tertiary structure- precise 3D shape of a single polypeptide, stabilised by R group interactions (i.e. hydrogen bonding, disulphide links, ionic interactions, hydrophobic interactions)
Quaternary structure- 2 or more polypeptides bonded together (R group interactions)
The formation of a disulphide bond
Strong, covalent bond between the R groups of two cysteine amino acids.
Food test for proteins
Add biuret reagent (dilute sodium hydroxide and copper sulphate solution)
Colour change from light blue to purple
Key features of a globular protein
E.g. haemoglobin
Polypeptide chains form a spherical shape
Often soluble
Hydrophilic R groups on the outside and hydrophobic on the inside
Sensitive to temperature and PH changes.
Key features of fibrous proteins
E.g. collagen
Polypeptide chains are parallel
Tensile with a structural role
List proteins
Enzymes e.g. amylase, rubisco, ATP synthase Cell surface carrier proteins Cell surface active transport pumps Cell surface receptor proteins (glycoproteins) Antibodies Some hormones e.g insulin, glucagon, ADH Plasma proteins Haemoglobin/ myoglobin Actin and myosin Collagen Keratin Electron carriers (Electron transfer chain molecules)
