1.4.1 General Properties Of Proteins

Question 1

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 and how do they vary

Answer 2

• 20
• 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 e.g. 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 (dependant 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 (||) sulphate)
2. Positive result = purple / lilac colour (indicating presence of peptide bonds)