Gene mutation and DNA repair - Spontaneous mutations

10 important questions on Gene mutation and DNA repair - Spontaneous mutations

What are the two categories the causes of mutations are in?

  • Spontaneous mutations;
  • Induced mutations.

What are the three types of chemical changes that spontaneous mutations can arise?

  • Depurination;
  • Deamination;
  • Tautomeric shift.

What is an apurinic site?

An apurinic site is the site where a purine is removed.
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When DNA replication occurs over an apurinic site, what is the probability that a mutation will occur?

The probability is 75%.

Which of these two changes is more difficult for DNA repair enzymes to fix correctly? Explain why.

The deamination of 5-methylcytosine is more difficult to repair because thymine is a base normally found in DNA. This makes it difficult for DNA repair enzymes to distinguish between the correct and altered strand.

What is a tautomeric shift?

A tautomeric shift is a temporary change in base structure. There are two forms, keto form and amino form. Thymine and Guanine are keto form. Adenine and Cytosine are amino form.

How does a tautomeric shift cause a mutation?

The tautomeric shift can cause a mutation when it occurs immediately prior to DNA replication.
When a thymine has undergone a tautomeric shift, a guanine will bind to it instead of an adenine and the other way around.
When a cytosine has undergone a tautomeric shift, an adenine will bind to it instead of a guanine, and the other way around.

What happens to the DNA of the daughter cells when a thymine base has undergone a tautomeric shift prior to DNA replication?

One strand will be normal. The other on will have a base mismatch. After a second round of DNA replication there will be 3 normal DNA molecules and 1 abnormal (with a mutation).

What is oxidative DNA damage? And what causes it?

Oxidative DNA damage is the change in DNA structure that is caused by ROS.

What is trinucleotide repeat expansion (TNRE)?

Trinucleotide repeat expansion is the phenomenon in which a repeated sequence of three nucleotides can readily increase in number from one generation to the next.

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