Question 1

The enzyme RNA polymerase synthesizes a specific RNA when provided with which of the following as a template?

Accepted Answer

RNA polymerase synthesizes RNA using a double-stranded DNA molecule as a template. The enzyme unwinds the double helix, reads the template strand, and synthesizes a complementary RNA molecule. The other answer choices (soluble RNA, ribosomal RNA, and messenger RNA) are types of RNA that are synthesized by different mechanisms and do not serve as templates for RNA polymerase. Single-stranded DNA is not a suitable template because it lacks a complementary strand for the enzyme to read.

Question 2

In a comparison of typical eukaryotic and prokaryotic mRNA, all of the following are true EXCEPT

Accepted Answer

Prokaryotic mRNA can be translated as it is being transcribed, a process called coupled transcription-translation, whereas eukaryotic mRNA must undergo post-transcriptional processing and be transported out of the nucleus before translation can occur. Therefore, statement D is false. The other statements are true.

Question 3

All of the following statements about the RNA polymerase are true EXCEPT which one?

Accepted Answer

RNA polymerase synthesizes RNA by using a DNA template, but the product (RNA) is not covalently linked to the DNA template. The RNA strand is synthesized complementary to the DNA template strand and is released once the transcription is complete.

Question 4

Small nuclear RNAs such as U1, U2 and U5 affect gene expression by

Accepted Answer

Small nuclear RNAs U1, U2 and U5 function as essential components of the spliceosome, which is responsible for removing introns and splicing exons together to form mature mRNA. Therefore, they play a crucial role in regulating gene expression by influencing mRNA splicing.

Question 5

Splicing of eukaryotic mRNA precursors involves all of the following EXCEPT

Accepted Answer

Although poly(A) polymerase is involved in the processing of mRNA, it is not directly involved in splicing of the mRNA precursor. The other answer choices are all involved in the splicing process.

Question 6

RNA polymerases in eukaryotic cells

Accepted Answer

RNA polymerases in eukaryotic cells exist in multiple molecular forms, referred to as RNA polymerase I, II, and III. These different polymerases have different specificities for different types of RNA molecules. For example, RNA polymerase II is responsible for transcribing protein-coding genes, while RNA polymerase III transcribes genes for tRNAs, 5S rRNA, and some other small RNA molecules.

Question 7

A characteristic of transcription by RNA polymerase II in eukaryotic cells is:

Accepted Answer

RNA polymerase II adds a modified nucleotide cap (7-methylguanosine) to the 5' end of the mRNA and a string of 100-250 adenine nucleotides to the 3' end in a process called capping and polyadenylation, respectively. These nucleotides are not encoded by DNA, hence covalent addition of these non-encoded nucleotides occurs during transcription.

Question 8

Many eukaryotic and some prokaryotic genes have their coding regions interrupted by introns (intervening sequences). These intronic sequences are removed

Accepted Answer

Intronic sequences are removed from pre-mRNA (also known as heterogeneous nuclear RNA) by a process called splicing, which results in the formation of mature mRNA that can then undergo translation to produce a functional protein. Introns are not removed during translation, polyadenylation is the addition of a poly-A tail to the 3' end of mRNA and does not affect introns, and nucleases are involved in the degradation of DNA and RNA but not specifically in the removal of introns. Transfer RNA does not typically contain introns.

Question 9

Which ONE of the following nuclear RNA processing events is correct?

Accepted Answer

The 5'-end of many RNAs is capped with a unique structure involving a 5'-5' triphosphate link to a 7-methylguanosine. This cap structure is critical for RNA stability, export from the nucleus, and translation initiation in eukaryotes. The other options describe processes that do not accurately represent RNA processing events.

Question 10

Splicing of pre-mRNA introns is accomplished by:

Accepted Answer

Splicing of pre-mRNA introns is accomplished by two transesterification reactions. During the first reaction, the 2'OH group of an adenosine residue within the intron attacks the phosphate at the 5' end of the intron, resulting in the formation of a lariat structure and the release of the 5' exon. During the second reaction, the 3'OH group of the 5' exon attacks the phosphate at the 3' end of the 3' exon, resulting in the release of the intron and the joining of the two exons. No ATP, no GTP, no guanosine, and no covalent attachment of the exon to the intron are involved in the splicing mechanism.

Question 11

Regarding RNA synthesis, which of the following statements is correct?

Accepted Answer

Choice A is incorrect as the rho subunit is involved in termination of transcription, not initiation. Choice B is correct as RNA polymerase reads the DNA template strand in the 3' to 5' direction and synthesizes the complementary RNA strand in the 5' to 3' direction. Choice C is also correct as the first nucleotides placed in an RNA transcript of prokaryotic cells are GTP and ATP. Therefore, E is the correct answer.

Question 12

Which statement is true?

Accepted Answer

Transcription of DNA to RNA initiates at a region of the DNA called a promoter region. This is where RNA polymerase binds to start transcription.

Question 13

Which of the following is not characteristic of tRNAs?

Accepted Answer

tRNAs do not contain codons; they contain anticodons that pair with the codons on mRNA during the process of translation. Codons are found on mRNA and dictate the amino acid sequence.

Question 14

Genes containing intervening sequences (or introns)

Accepted Answer

Genes containing intervening sequences, or introns, are common in eukaryotic cells. These introns do not code for proteins but are instead transcribed into mRNA precursors, which must be spliced before translation can occur. This splicing removes the introns and joins together the remaining exons to form a mature mRNA molecule.

Question 15

All of the following statements about RNA polymerase and DNA polymerase are correct EXCEPT

Accepted Answer

RNA polymerase does not require a primer to initiate synthesis, whereas DNA polymerase does.

Question 16

The beta-globin gene from a thalassemic patient was cloned and sequenced. The technician who characterized this gene informs you that a point mutation was found, but that it can not account for the thalassemia because the mutation occurred within an intron sequence. What doesn't the technician understand?

Accepted Answer

The technician doesn't understand that certain intron sequences are absolute requirements for splicing. These sequences are recognized by the spliceosome and are essential for the proper splicing of the pre-mRNA into the mature mRNA. Mutations in these sequences can result in aberrant splicing, which can lead to diseases such as thalassemia. Therefore, even though the mutation occurred within an intron, it could still be responsible for the thalassemia if it disrupted an essential splicing sequence.

Question 17

Leucine zipper domains found in many transcription factors function directly in

Accepted Answer

Leucine zipper domains are involved in dimerization, which allows the transcription factors to form functional complexes that can bind to DNA and activate transcription.

Question 18

All of the following statements about ribosomes are correct EXCEPT which one?

Accepted Answer

Mitochondria have 70S ribosomes, not 80S.

Question 19

Eukaryotic RNA polymerase II differs from the prokaryotic RNA polymerase because it

Accepted Answer

Eukaryotic RNA polymerase II requires multiple accessory proteins, whereas prokaryotic RNA polymerase does not.

(Note: A is incorrect because sigma factor is associated with prokaryotic RNA polymerase, not eukaryotic RNA polymerase II. B is incorrect because both prokaryotic and eukaryotic RNA polymerases can incorporate ribonucleotide precursors. D is incorrect because eukaryotic RNA polymerase II transcribes all protein-coding genes, not just ribosomal RNA genes. E is incorrect because termination in eukaryotes is typically mediated by different factors than in prokaryotes; eukaryotic RNA polymerase II interacts with a termination factor called TTF-I.)

Question 20

In what part of the mammalian cell is ribosomal RNA produced?

Accepted Answer

Ribosomal RNA is produced in the nucleolus of the mammalian cell. The nucleolus is a specialized organelle within the nucleus where ribosomal RNA is transcribed, processed, and assembled with ribosomal proteins to form ribosomes which are used for protein synthesis.

Quiz 5: RNA: Transcription and Rna Processing