Topic 1.4 - Proteins

Question 1

Describe the reaction which forms a dipeptide.

Answer 1

A condensation reaction between amine/NH2 group and carboxyl/COOH group produces a dipeptide
linked by a peptide bond, and releases a molecule of water.

Question 2

Describe the formation of a polypeptide

Answer 2

A polypeptide is formed by the condensation of MANY amino acids

Question 3

Primary structure

Answer 3

sequence of amino acids form a
polypeptide chain

Question 4

Bonds in primary structure

Answer 4

peptide bonds between the amino group and
the carboxyl group of the adjacent amino acid

Question 5

Secondary structure

Answer 5

polypeptide chain is folded to form
an alpha-helix or beta-pleated
sheet

Question 6

Bonds in secondary structure

Answer 6

Hydrogen bonding between NH of one amino
acid and C=O of another amino acid

Question 7

Tertiary structure

Answer 7

Further folding of the secondary
structure forms a unique 3-D
structure (can be globular or
fibrous)

Question 8

Bonding present in tertiary structure

Answer 8

disulphide bonds, hydrogen bonds and ionic
bonds between different R groups

Question 9

Quaternary structure

Answer 9

More than one polypeptide chain
folded and twisted. (Can also
contain a non-protein (prosthetic)
groups)

Question 10

The primary structure is fundamental in the formation of the subsequent structures. Explain why.

Answer 10

● A different sequence of amino acids means
● There are different R groups present
● So there is hydrogen, ionic, disulphide bonds in different places between different R groups
● which changes the tertiary structure
● which ultimately affects the function of protein

Question 11

7) Describe the Biuret Test for Proteins

Answer 11

The Biuret Test
● Add the NaOH
● copper sulphate (too)
● If it turns purple there is protein