Question

Draw a molecular diagram of the mRNA that would be transcribed by the sequence ATA in the sense strand of a molecule of DNA.

Short answer

The DNA sense strand sequence is ATA. Following the base pairing rules for RNA (A pairs with U and T pairs with A), the mRNA sequence transcribed would be UAU. The molecular diagram of the mRNA can be represented as a linear sequence: U-A-U.

Step-by-step solution

DNA Sequence

The given DNA sense strand sequence is ATA.

Base Pairing Rules

In RNA, A (adenine) pairs with U (uracil), T (thymine) pairs with A (adenine), C (cytosine) pairs with G (guanine), and G (guanine) pairs with C (cytosine).

Transcribing mRNA

Following the base pairing rules for RNA, the mRNA transcript for the DNA sense strand ATA would be: A pairs with U; T pairs with A and A pairs with U. So, the mRNA sequence is: UAU.

Molecular Diagram

To draw the molecular diagram, represent the mRNA strand as a linear sequence of the three bases: U-A-U.

Key concepts

Understanding the DNA Sense Strand

The DNA sense strand is crucial in understanding genetic transcription. It is one of the two strands in a DNA double helix and serves as the template for mRNA synthesis. Unlike the antisense strand, the sense strand has a sequence that corresponds to the mRNA's sequence, but with one notable exception: thymine (T) in DNA is replaced by uracil (U) in mRNA.

The process of transcription begins when RNA polymerase binds to the DNA and unwinds a small portion of the double helix to expose the sense strand. As it progresses, the RNA polymerase reads the DNA sense strand from the 3' end to the 5' end, although mRNA is synthesized in the 5' to 3' direction. This directional synthesis ensures that the mRNA strand is a correct copy of the gene's coding sequence, which subsequently determines the sequence of amino acids during translation.

RNA Base Pairing Rules

RNA base pairing rules are at the heart of transcribing DNA into mRNA. These rules dictate how nucleotide bases couple with one another during the process of transcription. In DNA, adenine (A) pairs with thymine (T), while cytosine (C) pairs with guanine (G). However, when RNA is synthesized, the pairing rules slightly change because RNA contains uracil (U) instead of thymine.

In RNA synthesis, adenine in DNA still pairs with uracil in RNA. Accordingly, for the given DNA sequence ATA, the adenine (A) at the first and last positions would pair with uracil (U), and the thymine (T) in the middle would pair with adenine (A) in the mRNA transcript. Following these pairing rules ensures that the genetic information is accurately copied from DNA to mRNA, which is then used to synthesize proteins during translation.

Molecular Diagram of mRNA

Creating a molecular diagram of mRNA provides a visual representation of the transcription process. For the DNA sense strand sequence ATA, the corresponding mRNA sequence, after applying RNA base pairing rules, would be UAU.

To depict this molecularly, each nucleotide is represented by its nitrogenous base connected to a sugar (ribose in the case of RNA) and a phosphate group, forming a single-stranded chain. The bases (U, A, U) are linked by phosphodiester bonds between their sugar groups, creating a backbone for the mRNA strand. This linear form of the molecule illustrates the order of bases and the way mRNA carries genetic information from the DNA to the cell's ribosomes, where proteins are synthesized. Understanding the molecular structure is fundamental for grasiting how the genetic code is translated into functional proteins.