Topic 1.4.1 General properties of proteins

Question 1

Draw / describe the general structure of an amino acid

Answer 1

● COOH = carboxyl group
● R = variable side chain / group
● H2N = amine group

Question 2

How many amino acids are common in all organisms? How do they vary?

Answer 2

The 20 amino acids that are common in all organisms differ only in their side group (R)

Question 3

Describe how amino acids join together

Answer 3

● Condensation reaction
● Removing a water molecule
● Between carboxyl / COOH group of one
and amine / NH2 group of another
● Forming a peptide bond

Question 4

What are dipeptides and polypeptides?

Answer 4

● Dipeptide - 2 amino acids joined together
● Polypeptide - many amino acids joined together

Question 5

Describe the primary structure of a protein

Answer 5

Sequence of amino acids in a polypeptide chain, joined by peptide bonds

Question 6

Describe the secondary structure of a protein

Answer 6

● Folding (repeating patterns) of polypeptide chain eg.
alpha helix / beta pleated sheets
● Due to hydrogen bonding between amino acids
● Between NH (group of one amino acid) and C=O (group)

Question 7

Describe the tertiary structure of a protein

Answer 7

● 3D folding of polypeptide chain
● Due to interactions between amino acid R groups
(dependent on sequence of amino acids)
● Forming hydrogen bonds, ionic bonds and disulfide bridges

Question 8

Describe the quaternary structure of a protein

Answer 8

● More than one polypeptide chain
● Formed by interactions between polypeptides
(hydrogen bonds, ionic bonds, disulfide bridges)

Question 9

Describe the test for proteins

Answer 9

1. Add biuret reagent (sodium hydroxide + copper (II) sulphate)
2. Positive result = purple / lilac colour (indicating presence of peptide bonds)