Question 1

You are working to characterize a novel protein in mice.Analysis shows that high levels of the primary transcript that codes for this protein are found in tissue from the brain, muscle, liver, and pancreas.However, an antibody that recognizes the C-terminal portion of the protein indicates that the protein is present in brain, muscle, and liver, but not in the pancreas.What is the most likely explanation for this result?

Accepted Answer

Alternative splicing in the pancreas may result in a protein variant that lacks the C-terminal portion recognized by the antibody, explaining why the protein is not detected in the pancreas despite the presence of the transcript.

Question 2

Eukaryotes have ____ type(s) of RNA polymerase.

Accepted Answer

Eukaryotes have three types of RNA polymerase: RNA polymerase I, II, and III, each responsible for transcribing different types of RNA.

Question 3

What is the likely consequence of a mutation that alters the branch point within an intron?

Accepted Answer

Failure to form a lariat is the likely consequence of a mutation that alters the branch point within an intron. The branch point is a specific sequence within the intron that is recognized by the spliceosome, a complex of proteins and RNA molecules that removes introns from pre-mRNA. If the branch point is mutated, the spliceosome will not be able to recognize it, and the intron will not be removed from the pre-mRNA. This will result in a mature mRNA that contains the intron, which will prevent the mRNA from being translated into protein.

Question 4

What would happen if snRNPs did not recognize the branch point within an intron?

Accepted Answer

Without recognition of the branch point, the snRNPs would not be able to form a lariat, which is necessary for proper splicing of introns from the pre-mRNA.

Question 5

In eukaryotes, each type of RNA polymerase recognizes a different

Accepted Answer

In eukaryotes, each type of RNA polymerase recognizes a different promoter, which is a specific DNA sequence that signals the start of transcription.

Question 6

Which molecule combines with proteins to form both the large and small ribosomal subunits?

Accepted Answer

Ribosomal RNA (rRNA) combines with proteins to form the large and small subunits of ribosomes, which are essential for protein synthesis in cells.

Question 7

Initiation of transcription differs from initiation of DNA replication in several ways.One difference is that initiation of transcription does not require

Accepted Answer

Initiation of transcription does not require a primer, which is required for initiation of DNA replication to initiate the synthesis of new DNA strands. Transcription uses a DNA template strand, as well as specific enzymes and a promoter to initiate gene expression.

Question 8

In prokaryotes, the RNA polymerase holoenzyme consists of

Accepted Answer

The RNA polymerase holoenzyme in prokaryotes consists of the core polymerase (which includes two alpha, one beta, and one beta' subunit) plus a sigma subunit, which is essential for initiating transcription.

Question 9

Cells conserve energy and resources by making active proteins only when they are needed.If a protein is not needed, which of the following methods of control would be the most energy-efficient?

Accepted Answer

Blocking transcription is the most energy-efficient method because it prevents the initial production of mRNA, thereby conserving resources that would be used in mRNA synthesis, translation, and potential degradation of unnecessary proteins.

Question 10

During protein synthesis in eukaryotes, what happens during RNA splicing?

Accepted Answer

During RNA splicing in eukaryotes, the primary transcript (pre-mRNA) is processed by removing introns and joining exons to form mature mRNA.

Question 11

During protein synthesis in eukaryotes, which molecule passes from the nucleus to the cytoplasm and specifies the sequence of amino acids in the new polypeptide?

Accepted Answer

mRNA (messenger RNA) is transcribed from DNA in the nucleus and then travels to the cytoplasm, where it serves as a template for protein synthesis, specifying the sequence of amino acids in the polypeptide.

Question 12

In eukaryotes, the 3' poly-A tail is attached to

Accepted Answer

The 3' poly-A tail is attached to mRNA in eukaryotes. This tail helps to protect the mRNA from degradation and also plays a role in translation.

Question 13

During the splicing reaction, the intron-exon junctions are recognized by

Accepted Answer

snRNPs (small nuclear ribonucleoproteins) are involved in recognizing the intron-exon junctions during the splicing reaction.

Question 14

Given the sentence "THE FAT CAT ATE THE RED RAT," which of the following would represent a frameshift mutation?

Accepted Answer

A frameshift mutation occurs when a nucleotide is inserted or deleted from the DNA sequence, causing a shift in the reading frame. In option C, there are several missing letters and extra spaces, causing the reading frame to shift and resulting in a frameshift mutation. Options A and B only involve substitutions and do not cause a frameshift mutation. Option D is the original sentence and does not involve any mutations.

Question 15

Eukaryotic pre-mRNA molecules are modified

Accepted Answer

Eukaryotic pre-mRNA molecules are modified inside the nucleus where processes like capping, polyadenylation, and splicing occur before the mRNA is exported to the cytoplasm.

Question 16

What is required for formation of the transcription initiation complex in eukaryotes?

Accepted Answer

In eukaryotes, the transcription initiation complex is formed when a transcription factor binds to the TATA box, which is a DNA sequence found in the promoter region. This initial binding is followed by the recruitment of additional transcription factors and RNA polymerase II, which is responsible for transcribing mRNA.

Question 17

The mutation responsible for Huntington's disease is a

Accepted Answer

The mutation responsible for Huntington's disease is a triplet repeat expansion mutation, specifically a CAG repeat expansion in the huntingtin gene. This results in an abnormally long glutamine stretch in the Huntingtin protein, which leads to neurodegeneration and the symptoms of the disease.

Question 18

Within the transcription bubble, the 9 most recently added nucleotides in the newly synthesized RNA strand temporarily form a helix with the template DNA strand.How might transcription be affected if helix formation did not occur?

Accepted Answer

The temporary helix formation stabilizes the 3' end of the RNA, aiding in proper elongation. Without it, the 3' end would be unstable, affecting elongation.

Question 19

Why are there fewer tRNA anticodons than the 61 needed to match each mRNA codon that codes for an amino acid?

Accepted Answer

The phenomenon known as "wobble base pairing" allows for flexibility in the pairing between the 3' base of the codon and the 5' base of the anticodon, enabling fewer tRNAs to recognize multiple codons.

Question 20

Two 6-base sequences are present in bacterial promoters: TATAAT (located 10 nt upstream from the start site) and TTGACA (located 35 nt upstream from the start site).What is the significance of the fact that these two base sequences are different?

Accepted Answer

The sequences help establish the location of the start site and the direction of transcription by serving as recognition sites for RNA polymerase and associated factors.

Quiz 15: Genes and How They Work