Question

What base is responsible for the hot spot for spontaneous point mutations?
A. 5-bromouracil
B. 5-methylcytosine
C. Guanine
D. Adenine

Answer 1

The DNA is the genetic material present inside the nucleus of the cells. It consists of four bases or nucleotides that make it up. These four bases are Adenine, guanine, cytosine, and thymine. DNA contains genes that regulate the functions of cells. The methylated form of cytosine is used in regulating gene expression.

Complete answer:
Spontaneous mutations refer to faulty alterations in the pairing of nucleotides in DNA (Deoxyribonucleic acid) during the replication process. Most of the spontaneous mutations are point mutations. This means that only a single base pair or nucleotide is placed wrongly in the DNA sequence. This wrong base causes faulty pairing and thus leads to many genetic diseases. The single mutation can change the reading frame for amino acid synthesis from that portion of DNA. Mostly the point mutations happen by replacement of the original base pair with its analogous substitute.
Option A is 5-bromouracil. It is the brominated form of uracil (a base pair in RNA in place of thymine). This nucleotide is analogous to the thymine base pair of DNA and usually incorporates into the DNA strand in its place. Now instead of pairing with thymine, the Adenine will pair with 5-bromouracil. This will lead to gene frame change causing spontaneous point mutation.
Option B is 5-methylcytosine. It is a methylated form of cytosine and is involved in the regulation of gene expression of DNA.
Option C is Guanine. It is one of the fundamental base pairs of DNA that make it along with cytosine, adenine, and thymine. It pairs with cytosine always with triple hydrogen bonds.
Option D is Adenine. Adenine is also one of the fundamental base pairs that make up DNA. It pairs with thymine with double hydrogen bonds.
Thus, the spontaneous point mutation is 5-bromouracil. So, the correct option is option A.

Note: There is a difference between spontaneous and induced mutations. They are mostly confused with each other. But the induced mutations are caused by chemical or physical agents like radiations or oxidative damage. The spontaneous mutations are the result of errors in the replication process or errors in deamination and depurination.