Problem 49 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

What is the complementary RNA sequence for the DNA segment AATCAGTT? (a) AAUCAGUU (b) CCAUCGAA (c) AACUGAUU (d) UUAGUCAA

Step-by-Step Solution

Answer

The correct complementary RNA sequence is (d) UUAGUCAA.

Step 1: Understanding DNA to RNA transcription

DNA and RNA are composed of nitrogenous bases. In DNA, the bases are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). RNA, however, contains Uracil (U) instead of Thymine. During transcription from DNA to RNA, the following base pairing occurs: A (in DNA) pairs with U (in RNA), T (in DNA) pairs with A (in RNA), C (in DNA) pairs with G (in RNA), and G (in DNA) pairs with C (in RNA).

Step 2: Identify base pairs

Given the DNA sequence AATCAGTT, we need to transcribe it into its complementary RNA sequence by replacing each base accordingly: A pairs with U, T pairs with A, C pairs with G, and G pairs with C.

Step 3: Transcribing the DNA sequence

For each base in the DNA sequence AATCAGTT, write the corresponding RNA base: - A (DNA) -> U (RNA) - A (DNA) -> U (RNA) - T (DNA) -> A (RNA) - C (DNA) -> G (RNA) - A (DNA) -> U (RNA) - G (DNA) -> C (RNA) - T (DNA) -> A (RNA) - T (DNA) -> A (RNA) Thus, the complementary RNA sequence is UUAGUCAA.

Step 4: Matching with given options

Now, compare the transcribed RNA sequence UUAGUCAA with the options provided: (a) AAUCAGUU (b) CCAUCGAA (c) AACUGAUU (d) UUAGUCAA The correct match is option (d).

Key Concepts

Complementary RNA Sequence

When discussing the conversion of DNA sequences into their RNA counterparts, we refer to the resulting strand as the complementary RNA sequence. In this process, each DNA base corresponds with a specific RNA base, forming a complementary strand that mirrors the DNA template, but with RNA bases. This is crucial in the transcription process, where genetic information from DNA is transcribed into a format that can be understood and utilized by cells to synthesize proteins. This means that the complementary RNA sequence contains the genetic instructions necessary for this synthesis, but in a version that RNA, not DNA, can comprehend.

Nitrogenous Bases

Nitrogenous bases are the building blocks of nucleic acids, like DNA and RNA, and consist of four main types. In DNA, these are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). RNA retains three of these bases—Adenine (A), Cytosine (C), and Guanine (G)—but instead of Thymine, RNA contains Uracil (U).
These bases pair specifically with each other due to their unique shapes and hydrogen bonding capabilities, forming the rungs on the ladder of DNA or RNA strands. The arrangement and sequence of these bases form the genetic codes that direct all cellular functions. Understanding these bases and their interactions is fundamental to grasping how genetic information is passed on and utilized in living organisms.

Base Pairing Rules

The base pairing rules are a set of guidelines that detail how nitrogenous bases pair up in DNA and RNA sequences. Adhering to these rules ensures that genetic information is accurately replicated and transcribed. In DNA, the base pairing works such that:

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

RNA follows a slightly different code where the pairing occurs as:

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

These rules are vital for the transcription process as they guide the creation of an accurate complementary RNA sequence from a DNA template.

Transcription Process

The transcription process is a key biological mechanism in which a DNA sequence is copied into an RNA sequence. This conversion is critical for gene expression, allowing cells to perform functions dictated by genetic code.
During transcription, an enzyme called RNA polymerase binds to the DNA and unwinds the double helix. It then reads the DNA strand and synthesizes a single strand of RNA by following the base pairing rules. This new RNA strand, known as messenger RNA (mRNA), leaves the nucleus and enters the cytoplasm where it directs the synthesis of proteins by ribosomes.
Understanding the transcription process is essential for comprehending how genes determine the traits and functions of living organisms, as it shows how genetic data is transformed into an active form that can influence cell behavior.