Biomolecules - Genetic Mutations

Question 1

Intro

Answer 1

• Sickle cell is caused by a mutation that changes glutamine to valine.
• mutations originate at the DNA a level
• the effect of mutations are usually found at the protein level
• mutations can be inherited or they might occur spontaneously from many sources e.g. environment, DNA replication errors etc.

Question 2

Types of mutation

Answer 2

Mutations are mistakes in a cells DNA that lead to abnormal protein production. We can classify mutations based on their effect on DNA and effect on protein.
- point mutations: one base in DNA is replaced with another and so only affects one amino acid
- frame shift mutation: one base is added; this changes the reading frame of the RNA; affects more amino acids
- nonsense mutation: any genetic mutation that leads to a sequence becoming a STOP sequence
- missense mutation: any genetic mutation that changes an amino acid from one to another. They can be silent if it doesn’t affect the protein. If it’s a conservative mutation, the new protein is the same type as the original. Non conservative mutations occur when the new protein is a different type from the original

Question 3

Causes of mutations

Answer 3

Point
- base substitution: a transition is a swap between purines (A, G) or pyrimidines (C,T). A trans version is when a purine is replaced with a pyrimidine or vice versa. A mispairing might lead to A and C pairing and G and T pairing.
Frameshift
- base addition
- base deletion
Large scale mutations (seen at the chromosomal level)
- translocation: Gene swapping between non homologous chromosomes
- chromosomal inversion: two genes on the same chromosome become swapped

Question 4

Mutagens and carcinogens

Answer 4

*A mutagen is a chemical substance or physical event that can cause genetic mutations. They are classified into:
- endogenous e.g. reactive oxygen species (produced by mitochondria- can break DNA and modify bases)
- exogenous e.g. intercalator (EtBr - sticks between the strands of DNA), base analogues (pretend to be a certain base but act differently)
*A carcinogen can be a mutagen, but it’s anything that can lead to cancer.
- work by making DNA mutations or increasing the rate of cell division
E.g. UV radiation, tobacco, asbestos

Question 5

Effects of mutation

Answer 5

Good mutations
- streptococcus pneumonia might have a mutation making it resistant to penicillin
Bad mutations
- cystic fibrosis is caused by a mutation in the CFTR gene making mucus in the lungs very thick making it hard to breathe.
Good and bad
- sickle cell disease is caused by a mutation in haemoglobin. The new form is less efficient at moving oxygen, but the host is less susceptible to malaria