proteins Flashcards
RP1
What is the general structure of an amino acid?
COOH = carboxyl group
R = variable side group consists of carbon chain and may include other functional group.
NH2 = amino group.
Describe how to test for proteins in a sample.
biuret test confirms the presence of peptide bond.
1. Add equal volume of sodium hydroxide to sample at room temp.
2. Add drops of dilute copper (||) sulfate solution. swirl to mix.
positive result - colour changes from BLUE to PURPLE.
negative result = solution remains BLUE.
How many amino acids are there and how do they differ from one another?
- all differ by R group.
How do dipeptides and polypeptides form?
condensation reaction forms PEPTIDE bond and eliminates molecule of water.
Dipeptide = 2 amino acids.
Polypeptide = 3 or more amino acids. joined in a process called polymerisation.
How many levels of protein structure are there?
4
Define primary structure of a protein.
Sequence of amino acids in a polypeptide chain.
Define secondary structure of a protein.
hydrogen bonds form between C=O of the carboxyl group and the -NH of amino group of different amino acids.
Name the two types of secondary protein structure.
alpha helix.
beta pleated sheet.
Describe the alpha helix.
Spiral shape.
Hydrogen bonds parallel to helical axis.
all N-H bonds on same side of the protein chain.
Describe the beta pleated sheet.
form by folding the chain back on itself in a zig-zag plane.
connected laterally by at least two or three backbone hydrogen bonds, forming a twisted, pleated sheet.
N-H and C=O groups alternate from one side to the other.
Define tertiary structure of a protein.
Name the bonds present.
the polypeptide chains are twisted and folded into a specific 3D structure.
- disulphide bridges.
- ionic bonds.
- hydrogen bonds.
Describe disulphide bridges in the tertiary structure.
strong covalent links between the sulfur atoms of two cysteine amino acids.
strong bonds = not easily broken.
Describe ionic bonds in the tertiary structure of proteins.
weaker than disulfide bridges but stronger than hydrogen bonds.
between R groups.
easily broken by changes to the pH.
Describe hydrogen bonds in the tertiary structure of proteins.
numerous and easily broken.
Define quaternary structure of a protein.
functional proteins may consist of more than one polypeptide.
precise 3D structure held together by the same types of bonds as tertiary structure.
may involve addition of prosthetic groups e.g. phosphate groups.
