Activity 19.1 Marking Scheme: Investigating The Primary Structure of Ribonuclease
Activity 19.1 Marking Scheme: Investigating The Primary Structure of Ribonuclease
Activity 19.1 Marking Scheme: Investigating The Primary Structure of Ribonuclease
1 marking scheme
Investigating the primary structure of ribonuclease
1 horse – 128
common minke whale – 124
red kangaroo – 122
2 K lysine
E glutamic acid
T threonine
A alanine
A alanine
A alanine
K lysine
F phenylalanine
E glutamic acid
R arginine
Q glutamine
H histidine
3
Position 1 2 3 4 5 6 7 8 9 10 11 12
Fig. 2.18 K E T A A A K F E R Q H
horse K E S P A M K F E R Q H
Position 1 2 3 4 5 6 7 8 9 10 11 12
Fig. 2.18 K E T A A A K F E R Q H
minke R E S P A M K F Q R Q H
whale
Position 1 2 3 4 5 6 7 8 9 10 11 12
Fig. 2.18 K E T A A A K F E R Q H
red E T P A E K F Q R Q H M
kangaroo
Position 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Fig. 2.18 K E T A A A K F E R Q H M D S
red E T P A E K F Q R Q H M D T E
kangaroo
Position 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Fig. 2.18 K E T A A A K F E R Q H M D S
red E T P A E K F Q R Q H M D T
kangaroo
This now shows that there are ten positions that are occupied by the same amino acids.
This suggests that the gene for pancreatic ribonuclease in the red kangaroo has one less triplet than
the genes for this enzyme in the other three mammals.
6 Tryptophan, W or Trp. It is found at position 39 in the horse ribonuclease.
No. Tryptophan is not in bovine ribonuclease.
7 Position 39 in bovine ribonuclease and minke whale ribonuclease is occupied by arginine (R or
Arg). The DNA triplets for this amino acid are GC_ (where _ represents any base, A, C, T or G),
TCT and TCC.
There is only one DNA triplet for tryptophan – ACC.
It is possible for the triplets TCC and GCC to change by a substitution mutation to ACC. This
would replace arginine by tryptophan in the amino acid sequence.
8 Cysteine (C). There are eight cysteine residues and, therefore, four disulfide bonds. They are at
positions: 26 – 84, 40 – 95, 58 – 110, 65 – 73
This sequence has 150 amino acids rather than 124 as shown in Figure 2.18 in the Coursebook.
This is because the full sequence has an additional 26 amino acids at the start of the sequence
(from position 27 on, the sequence is the same). This initial sequence of 26 amino acids is a signal
sequence or signal peptide at the N terminal of the protein. Signal peptides are present at the N
terminal of proteins that are secreted from cells. The cell uses the signal sequence to make sure the
protein passes through the endoplasmic reticulum and the Golgi body to enter a vesicle that
releases the protein by exocytosis. Ribonuclease is secreted from pancreatic cells into the
pancreatic duct and from there it passes into the small intestine.