proteins

Created by

ruby cook

Cards (14)

proteins differ from carbohydrates and lipids because they also contain nitrogen, some contain sulphur and some phosphorus
proteins are polymers made from amino acids
chains of amino acids are called polypeptides
there are 20 amino acids
amino acid basic structure -
attached to a central carbon
an N terminal - NH2
a C terminal - COOH
a hydrogen atom
an R group
at pH 7 an amino acid has both a negative and a positive charge (zwitterion)
formation of a peptide bond -
condensation reaction between the c terminal of one amino acid and the n terminal of another - makes a dipeptide (NH2-R1-R2-COOH)
primary structure - order of the amino acids in the peptide chain - determined by the base sequence on one DNA strand molecule
secondary structure - folding of the primary structure into alpha helices or beta pleated sheets
tertiary structure - the alpha helix of the secondary protein can be folded and twisted to form a more complex 3D shape.
the shape is maintained by - hydrogen/ionic/disulphide bonds and hydrophobic interactions
quaternary structure - when two or more polypeptides join together to make a larger protein, they are called subunits.
fibrous proteins are insoluble in water and are found in bones, ligaments and tendons. the polypeptides are in the form of long chains or sheets with many cross links which form long fibres - for example keratin (the protein in hair)
they are tough for example collagen which provides the strength needed in tendons
a fibre consists of of three identical polypeptide chains twisted around each other and linked by hydrogen bonds
globular protein - compact and folded into spherical molecules - this makes them water soluble.
functions include enzymes, antibodies, plasma proteins and hormones
consists of 4 folded polypeptide chains with the iron containing group haem at the centre of each
test for protein -
biuret test
add a few drops of biurets solution to a sample if protein is present biurets reagent turns purple