The sequence of nucleotides in mRNA is determined by the sequence of
nucleotides in
a. amino acids
b. DNA
c. tRNA
d. ribosomes
The Correct Answer and Explanation is :
The correct answer is b. DNA.
Explanation
The sequence of nucleotides in messenger RNA (mRNA) is directly determined by the sequence of nucleotides in DNA during a process known as transcription. DNA, which is the genetic blueprint of an organism, is composed of four types of nucleotides (adenine, thymine, cytosine, and guanine). Each segment of DNA that codes for a protein is called a gene.
During transcription, RNA polymerase, an enzyme, binds to a specific region of the DNA that contains a gene. The DNA strands unwind and separate, allowing the RNA polymerase to read the template strand of DNA. As it moves along the DNA, RNA polymerase synthesizes a complementary strand of RNA. Importantly, in RNA, uracil (U) replaces thymine (T), so whenever the enzyme encounters an adenine (A) on the DNA template, it adds a uracil (U) to the growing RNA strand.
The resulting mRNA molecule is a complementary copy of the gene, but it is single-stranded and contains uracil instead of thymine. This mRNA then undergoes several modifications, including splicing, capping, and polyadenylation, before it is transported out of the nucleus into the cytoplasm.
Once in the cytoplasm, the mRNA serves as a template for translation, where ribosomes read the sequence of nucleotides in sets of three, called codons. Each codon corresponds to a specific amino acid, which are the building blocks of proteins. Therefore, while tRNA and ribosomes play crucial roles in the translation of mRNA into proteins, the original sequence of mRNA is directly dictated by the DNA sequence. This central dogma of molecular biology—where DNA is transcribed into RNA, which is then translated into proteins—highlights the foundational relationship between these nucleic acids in the flow of genetic information.