Mutation

Question 1

Define mutation.

Answer 1

It is the change in number , sequence and structure of DNA.

Question 2

Define gene mutation.

Answer 2

Gene mutation is the change in nucleotide sequence of the DNA in a particular region of the chromosome. ‘

Question 3

How does missense mutation affect protein function?

Answer 3

Conservative: If the change is lysine>arginine , the amino acids have R-groups with similar properties as they are both positively charged. The resultant protein will fold in a similar way , have a similar 3D conformation and thus a similar protein function.

Non-conservative: If the change is from lysine-threonine , lysine is positively charged while threonine is polar uncharged. The resulting protein will fold differently , causing the 3D conformation to be different and resulting in a protein with a different function.

Question 4

What happens if nonsense mutation takes place?

Answer 4

It will result in the change of a codon to a stop codon. Translation will be terminated prematurely , resulting in a truncated polypeptide. Protein is the non-functional due to the loss of 3D conformation.

Question 5

How does sickle-cell anaemia form?

Answer 5

It is when HbS is formed instead of HbA due to mutation in the B globin gene coding for B-globin polypeptide in haemoglobin. Base-pair substitution from thymine to adenine in the DNA triplet for the sixth amino acid in the B-globin gene , causing the mRNA codon to change from GAG to GUG.

Instead of charged and hydrophilic glutamic acid , non-polar and hydrophobic valine is coded.

Resulting polypeptide folds differently , exposing hydrophobic patch on the outside of the protein. This hydrophobic patch may stick to other hydrophobic patch of other proteins .

Question 6

How does HbS change the phenotype of Haemoglobin?

Answer 6

When HbS releases oxygen , the hydrophobic patch sticks out and associates with other hydrophobic patches on HbS molecules, causing the polymerisation of HbS molecules and forming a rigid , rod-like fibre. This causes distorts the biconcave shape , forming the sickle-cell red blood cells.

Question 7

Sickle shaped RBCs are…?

Answer 7

-inefficient in transporting oxygen gsa
-clump and clog the blood capillaries , obstructing other cells from passing through > depriving organs from oxygen which can lead to organ failure
-has a shorter life span , causing it to break down easily resulting in anaemia
-accumulate in the spleen for destruction , causing enlargement of the spleen.

Question 8

Define chromosomal mutation.

Answer 8

Changes in the structure or number of chromosomes.