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Chapter 15: Problem 27

If mRNA is complementary to the DNA template strand and the DNA template stand is complementary to the DNA non-template strand, why are base sequences of mRNA and the DNA non- template strand not identical? Could they ever be? a. No, they cannot be identical because the T nucleotide in DNA is replaced with U nucleotide in RNA and AUG is the start codon. b. No, they cannot be identical because the T nucleotide in RNA is replaced with U nucleotide in DNA. c. They can be identical if methylation of the U nucleotide in RNA occurs and gives T nucleotide. d. They can be identical if de-methylation of the U nucleotide in RNA occurs and gives T nucleotide.

Short Answer

Expert verified
No, the sequences cannot be identical because RNA has Uracil (U) instead of Thymine (T) and AUG is the start codon.

Step by step solution

01

Understand the Relationship between DNA and mRNA

The mRNA is synthesized as a complementary strand to the DNA template strand. This means that each base in the mRNA is paired with its complementary base in the DNA template strand following the base-pairing rules: Adenine (A) with Thymine (T) in DNA, and Adenine (A) with Uracil (U) in RNA, Cytosine (C) with Guanine (G), and Guanine (G) with Cytosine (C).
02

Identify Differences in Base Pairing

Identify that in RNA, Uracil (U) replaces the DNA base Thymine (T). Therefore, even though mRNA is complementary to the DNA template strand and the DNA template strand is complementary to the DNA non-template strand, the presence of Uracil in mRNA and Thymine in DNA makes their base sequences not identical.
03

Analyze the Options Provided

Option a states that mRNA and DNA non-template strand cannot be identical because of the replacement of T with U, and mentions AUG as the start codon. Option b incorrectly states that T is replaced with U in DNA. Option c and d imply that U can undergo methylation or de-methylation to form T, making them identical.
04

Evaluate the Correctness of the Options

Option a is correct because it correctly identifies that U replaces T in RNA which makes the sequences non-identical and recognizes the role of AUG as the start codon. Options c and d are hypothetical and do not typically occur naturally. Option b is incorrect as it confuses RNA and DNA bases.
05

Conclusion

The correct answer is option a. The sequences of mRNA and the DNA non-template strand cannot be identical because in mRNA, the T nucleotide is replaced with U.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

mRNA synthesis
mRNA, or messenger RNA, plays a crucial role in translating the genetic information encoded in DNA into proteins. The process of creating mRNA from a DNA template is known as transcription. During transcription, RNA polymerase reads the DNA template strand and synthesizes an mRNA molecule that is complementary to this strand.
The mRNA sequence is built using ribonucleotides: adenine (A), uracil (U), cytosine (C), and guanine (G). It's important to note that uracil (U) in RNA replaces thymine (T), which is found in DNA. This switch is a key reason why mRNA sequences and DNA template strand sequences are not identical, even though they are complementary.
The mRNA then serves as a template for protein synthesis during translation, helping cells make the specific proteins that are essential for their functions.
complementary base pairing
Complementary base pairing is essential for the function and integrity of both DNA and RNA. It refers to the specific pairing between nucleotides: adenine (A) pairs with thymine (T) in DNA, or with uracil (U) in RNA, while cytosine (C) pairs with guanine (G) in both DNA and RNA.
This pairing is due to hydrogen bonds that form between these bases, ensuring that the genetic code is accurately replicated and transcribed. Complementary base pairing also facilitates the process of DNA replication and transcription. During replication, the DNA strands separate, and new DNA strands are formed using the original strands as templates, following the base-pairing rules.
In transcription, the DNA template strand pairs with RNA nucleotides to form the mRNA strand. The precision of base pairing is critical for the accuracy of genetic information transfer and for the proper function of proteins synthesized in the cell.
nucleotide replacement
Nucleotide replacement is a fundamental concept in understanding why DNA and RNA sequences are not identical. The major difference lies in one specific nucleotide: thymine (T) in DNA is replaced by uracil (U) in RNA. This replacement occurs because RNA needs to be distinct from DNA to fulfill its different role in the cell.
For example, consider a DNA template strand with the sequence 5'-ATCG-3'. The mRNA synthesized from this DNA template will not have thymine (T). Instead, it will have uracil (U). So, the sequence of the complementary mRNA will be 5'-UAGC-3'.
This difference is vital because it ensures that RNA functions properly during processes like protein synthesis without accidentally becoming part of the DNA. Furthermore, the uracil (U) can be readily identified by the cellular machinery, which helps prevent errors during transcription and translation.

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Most popular questions from this chapter

Which of the following features distinguishes eukaryotic transcription from bacterial transcription? a. Eukaryotic transcription does not start at a consensus sequence. b. Eukaryotic transcription does not require an initiation complex. c. Eukaryotic transcription and translation do not take place at the same time. d. Eukaryotic transcription does not require a termination sequence.

What part of central dogma is not always followed in viruses? a. The flow of information in HIV is from RNA to DNA, then back to RNA to proteins. Influenza viruses never go through DNA. b. The flow of information is from protein to RNA in HIV virus, while the influenza virus converts DNA to RNA. c. The flow of information is similar, but nucleic acids are synthesized as a result of translation in HIV and influenza viruses. d. The flow of information is from RNA to protein. This protein is used to synthesize the DNA of the viruses in HIV and influenza

Structure and function in biology result from both the presence of genetic information and the expression of that information. Some genes are continually expressed, whereas the expression of most genes is regulated, commonly at the level of transcription. At the initiation of transcription, the TATA-binding protein (TBP) provides access to the DNA strand to be transcribed. The 5鈥橳ATAAA3鈥� sequence called the TATA box is found in prokaryotes, archaebacteria, and eukaryotes. Even among eukarya, when the TATA box is not present among eukaryotes, the initiation of transcription involves TBP. Scientists attribute this common characteristic to the relative thermostability of the A-T interaction. Hydrogen bonds hold the two strands of the DNA double helix together. This type of bond has the smallest interaction energy of all intermolecular forces; as temperature increases, these bonds are broken. A. Explain the advantage, in terms of the energy required, which is provided by an AT-rich region in the sequence where transcription is initiated. B. The fact that the TATA box or the associated TBP are common to all domains provides evidence of common ancestry among all life. Pose a scientific question that would need to be addressed by a valid alternative explanation of this fact. C. A whole-genome survey of prokaryotes (Zheng and Wu, BMC Bioinformatics, 2010) showed that the relative amounts of guanine and cytosine in DNA poorly predicted the temperature range conditions that are suitable for an organism. Refine the question posed in part B, taking this result into account.

Which molecule in the central dogma can be compared to a disposable photocopy of a book kept on reserve in the library? a. DNA b. mRNA c. Protein d. tRNA

Only a fraction of DNA encodes proteins. The noncoding portion of a gene is referred to as the intron. The intron fraction depends upon the gene. Introns are rare in prokaryotic and mitochondrial DNA; in human nuclear DNA, this fraction is about 95%. The intron is transcribed into mRNA, but this noncoding mRNA is edited out before translation of the coding portion, or exon, of a gene. The edited exon segments are then spliced together by a spliceosome, a very large and complex collection of RNAs and proteins. Although introns do not encode proteins, they have functions. In particular, they amplify expression of the exon, although the mechanism is unknown. When introns are very long, which is common among mammalian genes with roles in development, they can significantly extend the time required to complete transcription. Analysis of genes common to different plant and animal species shows many shared intronic positions and base sequences, although in some organisms, such as yeast, many introns have been deleted. Because introns do not encode proteins, mutations can remain silent and accumulate. A. As described above, introns are ancestral remnants that are replicated because they do not disadvantage the organism. Consider the claim that introns are 鈥渏unk DNA.鈥� Evaluate the claim with supporting evidence. B. Introns may be retained during transcription. Explain how the retention of a transcribed intron between two transcribed exons within a gene could do the following: 鈥� block expression of one polypeptide sequence 鈥� increase expression of a polypeptide 鈥� alter the polypeptide expressed
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