Answer the following question in paragraph form. A) First, define the three diff
ID: 214384 • Letter: A
Question
Answer the following question in paragraph form. A) First, define the three different types of point mutations and explain the differences between them. B) Second, rank the likelihood of the three different types of point mutations having an effect on the phenotype and explain why. C) Discuss the effects of a nonsense mutation in a gene coding for a protein that is vital for the activity of ATP synthase in the mitochondria. First, what would the impact of this mutation (affecting ATP synthase) be on DNA structure, and on transcription and translation? D) Finally, what would the likely impact of this ATP synthase mutation be on cellular respiration and why?
Explanation / Answer
A) Point mutations- a single base change in DNA sequence. It is of three types-
Missense point mutation- A change in DNA sequence that changes the codon to a different amino acid. Not all missense mutations are deleterious, some changes can have no effect. It is often difficult to interpret the consequences of these mutations in causing disease because of the ambiquity of missense mutations.
Nonsense point mutation- A change in the genetic code that results in the coding for a stop codon rather than an amino acid. Generally, the truncated protein is non-functional or its function is impeded. A gene encoding t-RNA undergoes a mutational event in its anticodon region that enables it to recognise a mutant nonsense codon and permit completion of translation. Such a mutation is called as nonsense suppressor.
Silent point mutations- A change in the genetic sequence that doesnot change the protein sequence. This can occur because of redundancy in the genetic code where an amino acid may be encoded by multiple codons.
B) Missense point mutations may have an effect on phenotype.
Missense > Nonsense > silent mutation
Missense point mutation may change an amino acid to an another amino acid which may result in a disease. For example, Sickle cell anaemia is caused due to point mutation specially the missense mutation in which GAG codon converts into GUG, which encodes the amino acid valine rather than glutamic acid.
C) Nonsense mutation in gene ATP6 of mitochondria leads to Leigh syndrome which impairs the function and stability of ATP synthase complex (ATP production and oxidative phosphorylation is inhibited due to this nonsense mutation in ATP6 gene). It happens because of a nonsense mutation which results in the replacement of Thymine with Guanine at position 8993 (T8993G).
D) ATP6 mutations disturbs the ATP synthase activity by inhibiting the intraenzyme coupling of H+-transport with the c-ring rotation and making it unable to utilize the proton translocation down the membrane proton gradient for the phosphorylation of ADP, hence creating the bad effect of mutation on cellular respiration. This mutation results in ataxia, neuropathy, retinitis pigmentosa or as fatal encephalopathy (Leigh syndrome).