proteins

Question 1

the diagram shows the primary structure of part of a polypeptide. each shape represents an amino acid. identical amino acids have the same shape.
name the type of peptidase which will hydrolyse the bond between the identical amino acid shape.

Answer 1

endopeptidase;

Question 2

describe how the structure of a protein depends on the amino acids it contain. (5)

Answer 2

1. structure is determined by position of amino acid/R groups;
2. primary structure is sequence/order of amino acids;
3. secondary structure formed by hydrogen bonding (between amino acids);
4. tertiary structure formed by interactions (between R groups);
5. quaternary structure contains more than one polypeptide;

Question 3

describe a biochemical test to confirm the presence of protein in a solution. (2)

Answer 3

1. add biuret (reagent);
2. (positive result) purple/lilac/violet/mauve;

Question 4

a dipeptide consists of two amino acids joined by a peptide bond.
describe two other ways in which all dipeptides are similar and one way in which they differ. (3)

Answer 4

similarities
1. amine/NH2 (group at end);
2. carboxyl/COOH (group at end);
3. two R groups;
4. all contain C and H and N and O;

difference
5. variable/different R group(s);

Question 5

describe how a peptide bond is formed between two amino acids to form a dipeptide. (2)

Answer 5

1. condensation reaction/loss of water;
2. between amine/NH2 and carboxyl/COOH;

Question 6

the secondary structure of a polypeptide is produced by bonds between amino acids.
describe how. (2)

Answer 6

1. hydrogen bonds;
2. between NH (group of one amino acid) and C=0 (group);
   OR
   forming b-pleated sheets/a-helix;

Question 7

two proteins have the same number and type of amino acids but different tertiary structures.
explain why. (2)

Answer 7

1. different sequence of amino acids
   OR
   different primary structure;
2. forms ionic/hydrogen/disulfide bonds in different places;

Question 8

draw general structure of amino acid. (1)

Answer 8

R

H2N C COOH

                H

Question 9

the genetic code is described as degenerate.
what is meant by this? (1)

Answer 9

more than one codon codes for a single amino acid;