1.4.1 general properties of proteins

Question 1

Amino acids

Answer 1

Monomers from which proteins are made

20 common amino acids, differ only in their side group

Condensation reaction between 2 forms a peptide bond

Question 2

Dipeptide

Answer 2

2 amino acids joined

Question 3

Polypeptide

Answer 3

Many amino acids joined

Functional protein may contain one or more polypeptides

Question 4

Primary structure

Answer 4

Determines sequence of amino acids in a polypeptide chain

Slight change can lead to protein with different properties

Question 5

Secondary structure

Answer 5

Describes coiling of the polypeptide chain with hydrogen bonding between amine group of one amino acid and carboxyl of another

Between NH2 and C=O

Structures formed tend to be a-helix or b-pleated sheet

Question 6

Tertiary structure

Answer 6

Overall 3D structure of the polypeptide chain with hydrogen, ionic and disulphide bonds between the R groups

Question 7

Quaternary structure

Answer 7

Describes the shape of the molecule when several polypeptide chains are wound around each other

Often there may be a non-amino acid part to the molecule (prosthetic group)

Question 8

Test for proteins

Answer 8

Biuret test

1. Add biuret solution: sodium hydroxide + copper (II) sulfate
2. Protein present = purple colour (neg=blue)
3. Detects presence of peptide bonds

Question 9

Hydrogen bonds

Answer 9

Occur between the amine and the carboxyl groups