Question 1

What is the function of the group of amino acids on the RNA polymerase,called the rudder?

Accepted Answer

The group of amino acids on the RNA polymerase, called the rudder, moves the template and non-template strands of DNA through channels inside the enzyme. This helps ensure that the correct nucleotide is added to the growing RNA molecule in a processive and accurate manner.

Question 2

Which of the following does not occur in post-transcriptional modifications occurring in eukaryotic mRNAs?

Accepted Answer

RNA polymerase termination is a step in transcription and does not occur in post-transcriptional modifications. The other options - addition of a poly (A) tail, addition of a methyl-guanosine cap, and removal of introns - are all common post-transcriptional modifications in eukaryotic mRNAs.

Question 3

Figure 16.1
 
-The enzyme complex associated with DNA in the figure is _____.

Accepted Answer

C

Question 4

Eukaryotes have three nuclear RNA polymerases.The primary function of RNA polymerase II is _____.

Accepted Answer

RNA polymerase II is responsible for transcribing protein-coding genes.

Question 5

Put the following events of transcription in chronological order.
1)Sigma binds to the promoter region.
2)The double helix of DNA is unwound,breaking hydrogen bonds between complementary strands.
3)Sigma binds to RNA polymerase.
4)Sigma is released.
5)Transcription begins.

Accepted Answer

Sigma first binds to RNA polymerase, then it binds to the promoter region, the DNA double helix unwinds, transcription begins, and finally, sigma is released.

Question 6

Codons are three-base sequences that specify the addition of a single amino acid.How do eukaryotic codons and prokaryotic codons compare?

Accepted Answer

Codons are a nearly universal language among all organisms, meaning they are generally shared across both eukaryotic and prokaryotic organisms. While there are some minor variations in codon usage between these groups, the fundamental genetic code is largely the same. Therefore, choices A, B, and C are incorrect.

Question 7

As scientists were unraveling the mysteries associated with transcription and translation,they discovered there was not a one-to-one correspondence between nucleotide sequence of a gene and base sequence of the mRNA it codes for.They proposed the genes-in-pieces hypothesis.How can the genes-in-pieces hypothesis be explained?

Accepted Answer

Introns are noncoding segments of DNA that are transcribed into RNA but are removed during RNA processing, resulting in a mature mRNA that only includes exons.

Question 8

David Pribnow studied the base sequences of promoters in bacteria and bacterial viruses.He found two conserved regions in these promoters (the -10 box and the -35 box).What is the function of these two regions of the promoter?

Accepted Answer

The -10 box and the -35 box are recognized by the sigma subunit of RNA polymerase, which helps to initiate transcription by binding to the promoter region. Therefore, the function of these two regions is to bind the sigma subunit that is associated with RNA polymerase.

Question 9

Alpha-amanitin is a toxin produced by the death cap mushroom.It blocks the synthesis of mRNA.What effect would it have on health of the organism that ate death cap mushrooms?

Accepted Answer

Alpha-amanitin blocks the synthesis of mRNA, which is necessary for protein synthesis. Without protein synthesis, the organism would be unable to carry out essential cellular functions, eventually leading to death.

Question 10

Which molecule or reaction supplies the energy for polymerization of nucleotides in the process of transcription?

Accepted Answer

The phosphate bonds in nucleotide triphosphates, such as ATP and GTP, provide the energy for polymerization of nucleotides during transcription. The energy is released when the high-energy phosphate bond is broken, allowing for the monomers to be added to the growing RNA chain. The other choices, such as the interaction between RNA polymerase and the promoter, or the unwinding of the DNA molecule, are important steps in the transcription process, but they do not directly supply the energy for polymerization.

Question 11

During elongation,RNA polymerase has three prominent channels,or grooves.These channels provide sites for all of the following,except _____.

Accepted Answer

RNA polymerase has channels for the DNA template, entry of ribonucleoside triphosphates, and exit of the growing RNA strand, but not specifically for the exit of diphosphates.

Question 12

How are RNA hairpin turns related to termination?

Accepted Answer

RNA hairpin turns are formed by complementary base pairing within the RNA molecule, creating a structure that causes the RNA transcript to dissociate from the RNA polymerase, leading to termination of transcription.

Question 13

A primary transcript in the nucleus of a eukaryotic cell is _____ the functional mRNA,while a primary transcript in a prokaryotic cell is _____ the functional mRNA.

Accepted Answer

In eukaryotes, the primary transcript undergoes processing (splicing, capping, polyadenylation) to become functional mRNA, making it initially larger. In prokaryotes, the primary transcript is often the functional mRNA, so they are the same size.

Question 14

Death cap mushrooms produce a substance called alpha-amanitin.Alpha-amanitin efficiently blocks synthesis of mRNA,but not of tRNA or rRNA in eukaryotic organisms.How is that possible?

Accepted Answer

Alpha-amanitin efficiently interferes with the action of RNA polymerase II, but not RNA polymerase I or III. This is because RNA polymerase II is the enzyme responsible for mRNA synthesis, while RNA polymerase I and III are responsible for rRNA and tRNA synthesis, respectively. Therefore, alpha-amanitin is specific to inhibiting RNA polymerase II and blocking mRNA synthesis.

Question 15

Figure 16.2.
 
-Refer to Figure 16.2.The mRNA is smaller than the length of the DNA that codes for it because _____.

Accepted Answer

Post-transcriptional modification removes the introns, leaving only the exons to be spliced together to form the mature mRNA. This results in a smaller mRNA molecule than the original DNA coding sequence because the introns are not included in the final transcript.

Question 16

What molecule in the spliceosome lowers the activation energy so intron removal reactions can occur?

Accepted Answer

Ribozymes are RNA molecules that catalyze chemical reactions, including the intron removal reactions in the spliceosome. They lower the activation energy required for the reaction to occur, making it proceed more efficiently. While proteins are also involved in the spliceosome, they do not directly lower the activation energy of the reaction like ribozymes do. RNA polymerase is involved in transcription, not splicing. Autocatalysis by introns is not a known mechanism for intron removal in the spliceosome.

Question 17

If RNA polymerase is missing _____ then transcription initiation would not occur but elongation could.

Accepted Answer

Sigma is the subunit of the RNA polymerase holoenzyme that is responsible for recognizing and binding to the promoter region of DNA to initiate transcription. Without sigma, the RNA polymerase would not be able to recognize and bind to the promoter, so transcription initiation would not occur. However, once transcription has been initiated, elongation of the RNA transcript would be carried out by the core RNA polymerase enzyme even in the absence of sigma. Therefore, if sigma is missing, transcription initiation would not occur but elongation could still occur.

Question 18

Which of the following processes is central to the initiation of transcription?

Accepted Answer

The binding of sigma (a subunit of RNA polymerase) to the promoter region (a sequence of DNA that initiates transcription) is central to the initiation of transcription in prokaryotes. This binding enables RNA polymerase to recognize and bind to the promoter, leading to the unwinding of the DNA double helix and the initiation of RNA synthesis.

Question 19

Which of the following is part of a DNA molecule?

Accepted Answer

Promoters are specific DNA sequences that signal the beginning of a gene and provide a binding site for RNA polymerase, the enzyme responsible for transcription. Sigma, holoenzyme, and initiation factors are all components of the bacterial transcription machinery, but are not part of the DNA molecule itself.

Question 20

The TATA box of the eukaryotic promoter is analogous to which structure of the prokaryotic promoter?

Accepted Answer

The TATA box of the eukaryotic promoter and the -10 box of the prokaryotic promoter are similar in that they serve as recognition sites for RNA polymerase to bind and initiate transcription. The -35 box of the prokaryotic promoter is also recognized by RNA polymerase but serves a different function than the TATA box. The site of initiation is not a structure within the promoter, but rather the point at which transcription actually begins. Sigma is a subunit of prokaryotic RNA polymerase that helps to recognize the promoter region and facilitate transcription initiation, but it is not directly analogous to the TATA box.

Quiz 16: Transcription and Translation