proteins Flashcards
what is an amino acid?
a monomer of protein
how many amino acids are there and how do they differ from one another? (2)
● 20
● differ only by side ‘R’ group
what is the general structure of an amino acid? (4)
● amine (-NH₂)
● R (variable)
● hydrogen
● carboxyl (-COOH)
draw an amino acid
draw a simplified amino acid
what is formed when two amino acids join together by condensation? (2)
● dipeptide
● water
what bond forms between two amino acids? (2)
● peptide bond
● between carboxyl group of one amino acid and amine group of another amino acid (-CONH-)
draw a dipeptide
what is formed when many amino acids join together by condensation? (2)
● polypeptide
● water
what is a protein? (2)
● a polymer
● formed by long chains of amino acids joined together by peptide bonds
define ‘primary structure’ of a protein (3)
● number and sequence of amino acids joined by peptide bonds
● proteins differ from each other as their primary structures are different
● determined by DNA sequence
define ‘secondary structure’ of a protein (4)
● hydrogen bonds form between carboxyl and amine groups
● there are two shapes that can form within proteins due to the hydrogen bonds:
● α-helix (spiral)
● β-pleated sheet
define ‘tertiary structure’ of a protein (5)
● formed by interactions between R groups
● shape is help together by bonds between R groups
● hydrogen bonds - weak
● ionic bonds - weak, form between oppositely charged R groups
● disulphide bonds - only cysteine amino acids (as they contain sulfur)
define ‘quaternary structure’ of a protein (3)
● formed by interactions between polypeptides
● more than one polypeptide chain
● e.g. haemoglobin
what happens when you heat protein? (4)
● increasing temp increases KE of molecules, making them vibrate
● breaks weak bonds holding structure together
● shape of molecule is lost
● denaturation
what happens when there’s a change in proteins pH? (3)
● disrupts ionic bonds in the tertiary structure
● shape of molecule is lost
● denaturation
describe the biuret test for proteins (4)
● add sodium hydroxide
● add drops of copper sulfate
● positive result: colour change is blue to
mauve
● negative result: stays blue
