MUTATIONS
There are many environmental factors (e.g. UV radiation) that could cause gene mutations but it can also be inherited.
When the DNA is being built an incorrect base may slip into place which could cause a mutation in the gene. If this mutation occurs in the reproductive organs, the DNA will be replicated in the sperm / egg cell and so the fertilized zygote will have the mutated gene in every cell.
Any mutations that occur in sections of DNA that don’t play a role in protein synthesis have no affect on the organism.
Sickle Cell Anaemia
- Mutation occurs in gene coding for haemoglobin; the A replaces the T as a base
- When mRNA is produced, it forms a complimentary base U (instead of A)
- The codon now codes for the amino acid Valine which is non – polar and therefore less soluble in water
- The haemoglobin is now less soluble
- When oxygen levels are low the oxygen molecules form long sticky fibres inside the RBC as there is no soluble amino acids to prevent them from doing this
- The shape of the RBC becomes distorted into
- This sickle shape means that the haemoglobin is able to carry around less oxygen as well as increase the risk of atherosclerosis and thrombosis
Cystic Fibrosis
Chromosome 7 carries the code to make the CFTR protein.
Why is it caused?
ATP energy is unable to bind to the ATP binding site thus the chloride ion channel cannot open and let the chloride through. The concentration gradient alters the electric gradient, which in term affects the net flow of water via osmosis. The water is drawn out from the mucus to maintain equilibrium, and so the mucus is more dry and sticky. It is able to trap more bacteria and dust hence cystic fibrosis is the result.
Most common way it’s caused (DF508):
- 3 nucleotides are deleted so there is a loss on one amino acid
- The CFTR protein shape is altered and it cannot fold into the correct shape
- The protein reduces the movement of Cl ions through channels as the Cl cannot fit into the shapes properly