gene mutation

Question 1

missense mutation

Answer 1

-altered codon after substitution codes for a different amino acid
- new amino acid coded for may have different property due to different R group which will change the polypeptide sequence and hence the protein’s specific 3D conformation

Question 2

nonsense mutation

Answer 2

• codon coding for an amino acid changing to a stop codon
• translation is terminated prematurely. a truncated/shortened polypeptide would be produced

Question 3

silent mutation

Answer 3

-although mRNA codon is changed, it still codes for the same amino acid
- this is due to the degeneracy of the genetic code where more than one codon can code for the same amino acid

Question 4

addition/deletion

Answer 4

-addition/deletion is a mutation defined as the gain or loss of one or more nucleotide base pairs in a gene
-alter the reading frame. all nucleotides downstream from the mutation will be improperly grouped into incorrect codons and incorrect codons ( frameshift mutation)

Question 5

sickle cell anaemia

Answer 5

-this is due to a single base pair substitution whereby adenine replaces thymine in the gene that codes for the β chain
- in the MRNA formed, GUG is coded for instead of GAG, resulting in missense mutation
- hydrophobic valine replaces hydrophilic glutamic acid. this results in a the change in the 3D conformation of haemoglobin

Question 6

characteristics of sickle cell anaemia

Answer 6

-substitution decreases the solubility of deoxygenated HbS
- at low oxygen concentration. hydrophobic areas of different HbS molecules would stick together
-HbS molecules will polymerise and precipitate out of solution to form rigid fibres
- this cuases red blood cells to change from circular to biconcave shape to sickle shape