Sickle Cell Haemoglobin - Extension Activity
Aim: To learn about the consequences of a base substitution mutation.
The DNA sequence below is the beginning of the coding region for the
beta chain of normal human haemoglobin.
(1) Let’s do some transcription. Write the complementary mRNA
sequence in the table using this template DNA sequence:
DNA
C
A
C
G
T
G
G
A
C
T
G
A
G
G
A
C
T
C
C
T
C
mRNA
(2) Using the Genetic Code translation table, write the three letter names of the amino
acids in the polypeptide that would be made by translation of the mRNA sequence.
Amino
Acids
© David Faure, InThinking www.biology-inthinking.co.uk
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Sickle Cell Haemoglobin - Extension Activity
Sickle cell haemoglobin has one different amino acid from ‘normal’ haemoglobin.
The sixth amino acid Glu (glutamic acid) is replaced with the amino acid Val (valine).
(3) Circle the sixth amino acid in the polypeptide.
(4) Remember that a codon consists of three bases, circle the sixth codon in both the DNA
and mRNA sequences above.
The mutation that produces sickle cell haemoglobin is a single base substitution (one DNA
base is different) in the sixth codon. At some time in history this mutation created a new
allele for this haemoglobin gene which causes Sickle cell disease.
(5) Using the Genetic Code translation table, list all the mRNA codons which code for
Valine (Val)
…………………………………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………………..
(6) Which mRNA base must be the one which is substituted in the sixth codon that would
result in the change of Glu (glutamic acid), whose mRNA codon is GAG into Val (valine).
…………………………………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………………..
(7) Complete mRNA base sequence which codes for the sickle cell haemoglobin.
mRNA
G
U
G
C
A
C
(8) Complete DNA base sequence which codes for the sickle cell haemoglobin.
DNA
C
A
C
G
T
G
G
A
C
(9) Using the diagrams you have done, explain how the DNA code has mutated in this base
substitution mutation.
…………………………………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………………..
© David Faure, InThinking www.biology-inthinking.co.uk
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