Question

You have just sequenced a piece of DNA that reads as follows: 5?—TCTTTGAGACATCC—3? What would be the base sequence in the mRNA transcribed from this DNA? A. 5?-AGAAACUCUGUAGG-3? B. 5?-GGAUGUCUCAAAGA-3? C. 5?-AGAAACTCTGTAGG-3? D. 5?-GGATGTCTCAAAGA-3?

Short answer

The correct mRNA sequence is B: 5'—GGAUGUCUCAAAGA—3'.

Step-by-step solution

Understanding the DNA Sequence

The given DNA sequence is 5'—TCTTTGAGACATCC—3'. Remember, transcription involves creating an mRNA strand that is complementary to the DNA template strand.

Identify the Complementary Strand

To transcribe this DNA sequence, identify the complementary base pairs. Adenine (A) pairs with Uracil (U) in RNA, Thymine (T) pairs with Adenine (A), Cytosine (C) pairs with Guanine (G), and Guanine (G) pairs with Cytosine (C).

Form the mRNA Sequence

Transcribe the given DNA sequence by replacing each DNA base with its complementary RNA base. For the sequence 5'—TCTTTGAGACATCC—3', the complementary RNA sequence will be: 3'—AGAAACUCUGUAGG—5'

Reverse the mRNA Sequence

The mRNA sequence should be written in the 5' to 3' direction. Reverse the previously formed complementary RNA sequence from 3'–5' to 5'–3'. This will give: 5'—GGAUGUCUCAAAGA—3'.

Match with Given Options

Compare the transcribed mRNA sequence with the given options. The correct match is B: 5'—GGAUGUCUCAAAGA—3'.

Key concepts

DNA sequence

A DNA sequence is a specific arrangement of nucleotides, which are the building blocks of DNA. Nucleotides consist of a sugar, a phosphate group, and a nitrogenous base. The four nitrogenous bases in DNA are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). Together, these base pairs form the genetic instructions for the development, functioning, growth, and reproduction of all organisms. In the exercise, the given DNA sequence is 5'—TCTTTGAGACATCC—3'. This specific sequence provides the template for creating a corresponding mRNA strand during the process known as transcription.

mRNA transcription

mRNA transcription is the process by which a section of DNA is copied into messenger RNA (mRNA). This happens inside the cell nucleus. During transcription, an enzyme called RNA polymerase binds to the DNA at a specific region called the promoter. It then separates the DNA strands and uses one strand as a template to synthesize a single-stranded mRNA molecule. This mRNA sequence is complementary to the DNA template strand. For example, the provided DNA strand 5'—TCTTTGAGACATCC—3' is used to create a complementary mRNA strand during transcription.

Complementary base pairing

Complementary base pairing is a fundamental principle in molecular biology where specific nitrogenous bases pair together. In DNA, Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G). During the transcription process, this pairing rule changes slightly because RNA uses Uracil (U) instead of Thymine. In RNA, Adenine (A) pairs with Uracil (U), while the Cytosine (C) pairs with Guanine (G) rule remains the same. Thus, to transcribe the DNA sequence 5'—TCTTTGAGACATCC—3', the complementary mRNA strand will be 3'—AGAAACUCUGUAGG—5'.

RNA base pairs

RNA base pairs are the nitrogenous bases that form pairs during the creation of RNA from a DNA template. The RNA bases include Adenine (A), Uracil (U), Cytosine (C), and Guanine (G). During transcription, these bases pair up with their DNA counterparts according to specific rules:

• Adenine (A) pairs with Uracil (U)
• Thymine (T) pairs with Adenine (A)
• Cytosine (C) pairs with Guanine (G)
• Guanine (G) pairs with Cytosine (C)

To get the mRNA sequence from the DNA sequence 5'—TCTTTGAGACATCC—3', we replace each DNA base with its complementary RNA base, resulting in the mRNA strand 5'—GGAUGUCUCAAAGA—3'. This sequence can be matched with one of the provided options, confirming the correct answer is B.