Conserved Proteins Quiz

Eukaryotic mRNAs have well-defined 3' ends terminating in poly(A) tails of approximately 250 nucleotides. This poly(A) tail plays a crucial role in mRNA stability, transport, and translation. It helps protect the mRNA from degradation and allows it to be recognized and bound by specific proteins involved in various cellular processes. In contrast, prokaryotic mRNAs do not typically possess poly(A) tails and have different mechanisms for regulating mRNA stability and translation.

In eukaryotic cells, mRNAs are synthesized in the nucleus through a process called transcription. The DNA is transcribed into pre-mRNA, which is then processed and modified to form mature mRNA. After mRNA synthesis, it is transported out of the nucleus into the cytosol, where most of the translation process occurs. Translation is the process of protein synthesis, where the mRNA is used as a template to assemble amino acids into a polypeptide chain. Therefore, the correct answer is nucleus, cytosol.

RNA interference is a mechanism in which small RNA molecules, such as microRNAs, bind to and degrade or inhibit the translation of specific messenger RNA (mRNA) molecules. This process leads to gene silencing, where the expression of a particular gene is reduced or completely turned off. Therefore, the correct answer is gene silencing.

snRNAs, or small nuclear ribonucleoproteins, are essential factors that mediate splicing. They form complexes with proteins to create spliceosomes, which are responsible for removing introns and joining exons during mRNA processing. These snRNAs recognize specific sequences at the splice sites and catalyze the splicing reaction. Promoters, TBP (TATA-binding protein), SMURFs, and TAFs (TBP-associated factors) are not directly involved in the splicing process.

The preinitiation complex begins to form at a TATA box-containing eukaryotic promoter when the TATA-binding protein binds to the TATA box. This binding event is crucial for the recruitment of other transcription factors and RNA polymerase to the promoter region, leading to the initiation of transcription. The TATA box serves as a recognition site for the TATA-binding protein, which then helps to position the RNA polymerase at the correct location on the DNA template for transcription to begin.

Eukaryote RNA polymerase recognize the different promoters with the help of transcription factors.

Option E was also accepted.

Prokaryotic mRNA encodes multiple proteins because it is polycistronic. In prokaryotes, a single mRNA molecule can contain multiple coding regions called cistrons, each encoding a different protein. This is possible due to the presence of Shine-Dalgarno sequences and ribosome binding sites within the mRNA molecule, which allow multiple ribosomes to simultaneously bind and initiate translation at different start codons along the mRNA. As a result, multiple proteins can be produced from a single mRNA transcript in prokaryotes.

RNA transcription is the process by which genetic information from DNA is copied into RNA. In this process, immobile protein complexes act as a machinery to reel in the DNA template and synthesize RNA molecules. Therefore, the correct answer is DNA, as it is the template from which RNA is transcribed.

During the shift from initiation to elongation in eukaryotes, RNA polymerase undergoes structural changes, including phosphorylation of its C-terminal domain. Phosphorylation refers to the addition of a phosphate group to a molecule, which can regulate protein activity and function. In this case, phosphorylation of the C-terminal domain of RNA polymerase is necessary for the transition from initiation to elongation, indicating that this modification plays a crucial role in the regulation of transcription in eukaryotes.

Eukaryotic transcription involves transcription factors, which are proteins that bind to specific DNA sequences called promoters. These transcription factors facilitate transcription by interacting with the DNA and other proteins involved in the transcription process. This interaction helps to recruit the RNA polymerase enzyme to the promoter and initiate transcription. Therefore, the statement that "It involves transcription factors, which facilitate transcription through protein-DNA and protein-protein interactions" is true.

Euchromatin is the correct answer because it refers to the portion of DNA that is actively transcribed and involved in gene expression in eukaryotic cells. Euchromatin is less condensed and more accessible to transcription factors and RNA polymerase, allowing for gene expression. In contrast, heterochromatin is highly condensed and transcriptionally inactive. Cytosol, endoplasmic reticulum, and liposomes are not directly involved in containing transcriptionally active DNA in eukaryotes.

The correct answer is to use siRNA to target the mRNA transcript encoding the aberrant protein and stop its production. siRNA is a powerful tool used to specifically silence the expression of a target gene by degrading its mRNA. By targeting the mRNA transcript encoding the aberrant protein, siRNA can effectively reduce its expression within the cell. This approach allows for a direct and specific manipulation of the protein levels, providing valuable insights into its impact on cellular function. The other options mentioned, such as adding Neomycin, lactose, or an inhibitor of cellular DNA polymerase, do not directly target the mRNA transcript of the aberrant protein and would not be effective in reducing its expression.

Exons are the expressed sequences of eukaryotic pre-mRNAs. They are the coding regions of the gene that are transcribed into mRNA and eventually translated into protein. Introns, on the other hand, are non-coding regions that are removed during RNA splicing. Operons are found in prokaryotes and consist of multiple genes controlled by a single promoter. Promoters are DNA sequences that initiate transcription. AUG box is a sequence found in the mRNA that signals the start of translation.

The phosphorylation of the CTD of RNA polymerase II is important for the progression from initiation to elongation phase of transcription. This phosphorylation event allows for the recruitment of factors that are necessary for the transition from the initiation complex to the elongation complex. It also facilitates the release of RNA polymerase II from the promoter and allows it to start transcribing the DNA template. Therefore, the phosphorylation of the CTD is crucial for the efficient and successful progression of transcription from initiation to elongation.

Splicing is the correct answer because it is a process in which the non-coding regions (introns) are removed from the pre-mRNA molecule, and the coding regions (exons) are joined together to form the mature mRNA. This process allows for the production of multiple proteins from one gene, as different combinations of exons can be spliced together to generate different mRNA transcripts and subsequently different protein products.

When an activator binds to the enhancer, a protein complex known as Mediator links the enhancer-bound activator to the transcription machinery poised at the promoter. The promoter is a region of DNA that signals the start of a gene and is responsible for initiating transcription. The Mediator complex helps in facilitating the communication between the activator and the transcription machinery, allowing for the efficient initiation of gene expression.

TFIIG is not one of the six highly conserved proteins that initiate transcription in eukaryotes. The other options, TFIIA, TFIIB, TFIID, TFIIF, and TFIIG, are all part of the transcription initiation complex and play crucial roles in the process. However, TFIIG is not a known protein involved in transcription initiation, making it the correct answer.

During transcription, the DNA strands separate, and RNA polymerase constructs an RNA molecule that forms a short hybrid helix with the template strand. The template strand is the strand of DNA that is used as a template to synthesize the complementary RNA molecule. RNA polymerase recognizes and binds to a specific region on the template strand, and then moves along the strand, adding complementary RNA nucleotides to form the RNA molecule. Therefore, the template strand is the correct answer as it is the strand of DNA that is directly involved in the synthesis of RNA during transcription.

The statement that promoters are recognized by siRNA is false. Promoters are typically recognized by transcription factors, which are proteins that bind to specific DNA sequences to regulate gene expression. siRNA (small interfering RNA) is involved in post-transcriptional gene silencing and does not directly recognize promoters.

In the absence of allolactose, the lac repressor protein binds to the operator, which is a DNA sequence near the lac operon. This binding prevents the transcription machinery from accessing the promoter region, thus inhibiting transcription of the genes involved in lactose metabolism. This mechanism ensures that the lac operon is not transcribed when lactose is not available as an energy source.

The TATA-binding protein (TBP), a subunit of TFIID, binds the TATA box and aids in transcription initiation. This is because the TATA box is a canonical sequence found in eukaryotic promoter regions that marks the site of transcription initiation. TBP specifically recognizes and binds to the TATA box, which helps to recruit RNA polymerase and initiate transcription.

Methylation of the promoters is not a way that transcriptionally inactive DNA maintains a condensed state. Methylation of the promoters can actually lead to gene silencing and inhibition of transcription. In contrast, chromatin remodeling can involve the presence of variant histones, changes in the pattern of histone modification, and the histone code, all of which can contribute to maintaining a condensed state of DNA and inhibiting transcription. Additionally, the degree of DNA methylation can also play a role in gene regulation, with highly methylated DNA often associated with transcriptional silencing.

RNA-DNA hybrids are observed during both replication and transcription in both eukaryotic and prokaryotic organisms. In replication, RNA primers are used to initiate DNA synthesis, resulting in RNA-DNA hybrids. In transcription, RNA molecules are synthesized using DNA as a template, forming RNA-DNA hybrids. Therefore, the correct answer is that RNA-DNA hybrids are observed during both replication and transcription in both eukaryotic and prokaryotic organisms.

Eukaryotic rRNA genes are processed in the nucleolus. The nucleolus is a specialized region within the nucleus where ribosomal RNA (rRNA) is transcribed, processed, and assembled into ribosomes. This process involves the removal of non-coding regions, called introns, from the primary rRNA transcript. After processing, the mature rRNA molecules are exported to the cytoplasm where they combine with proteins to form ribosomes. This statement accurately describes the location and process of rRNA gene processing in eukaryotic cells.

Sigma factors are proteins that bind to RNA polymerase and direct it to specific promoters on the DNA molecule. These promoters contain consensus sequences, such as the TATA box, that are recognized by sigma factors. By binding to different sigma factors, RNA polymerase can recognize different promoters and initiate transcription of specific genes. Therefore, a cell's complement of sigma factors determines which of its genes are transcribed.