DNA And RNA Transcription, Translation And Transport Quiz

Explanation
Pararetroviruses are a class of DNA viruses that are capable of reverse transcription. Reverse transcription is a process in which the viral RNA genome is converted into DNA by the enzyme reverse transcriptase. This DNA can then integrate into the host cell's genome and be transcribed and translated to produce viral proteins. Therefore, the statement that Pararetroviruses (Class VII) carry out reverse transcription is true.

Explanation
AP-1, AP-2, Sp1, and NF-κB are all transcription factors that are involved in HIV-1 transcription. These transcription factors play a crucial role in regulating the expression of HIV-1 genes by binding to specific DNA sequences in the viral promoter region. AP-1 and AP-2 are activator proteins that enhance HIV-1 transcription, while Sp1 is a stimulatory protein that also promotes transcription. NF-κB is a nuclear factor that is activated during HIV-1 infection and plays a key role in the transcriptional activation of viral genes. Therefore, all of these transcription factors are involved in HIV-1 transcription.

Explanation
When classes IV and VI viruses infect cells, only the Class IV genomes can function as mRNA. This means that the genetic material of Class IV viruses can directly serve as a template for protein synthesis, while the genomes of Class VI viruses cannot. Therefore, the statement is true.

Explanation
Some viruses are known to be tissue-specific, meaning they infect and replicate in specific types of cells or tissues in the body. This statement suggests that tissue-specific transcription factors, which are proteins that control the expression of genes in specific tissues, are required by some viruses. This implies that these viruses have evolved to exploit the cellular machinery of specific tissues in order to infect and replicate effectively. Therefore, the statement is true as it provides a plausible explanation for why some viruses exhibit tissue-specificity.

Explanation
In a (+) RNA genome, the RNA strand has the same sequence as the corresponding mRNA. This means that the RNA genome can directly serve as a template for protein synthesis without the need for any additional steps or modifications. Therefore, the statement is true.

Explanation
The given consensus sequence, TATAAA/TAA/G, is indeed present in the promoters of many eukaryotic cell and virus genes. This sequence, known as the TATA box, is crucial for the binding of transcription factors and the initiation of transcription. It helps in positioning the RNA polymerase at the correct site on the DNA, allowing for the efficient transcription of genes. Therefore, the statement "TRUE" is correct.

Explanation
Some viruses have the ability to produce their own transcription factors. For example, the herpes simplex virus VP16 is a component of the virus particle itself, while the human T cell leukemia virus I Tax protein is produced within the infected cell. This means that the statement is true.

Explanation
The statement is true because viruses that replicate in the nucleus of a cell rely on the cell's enzymes to complete their replication process. This is because the nucleus is where the cell's genetic material is located, so the virus needs to utilize the cell's machinery to access and replicate its own genetic material. On the other hand, viruses that replicate in the cytoplasm of a cell have evolved to encode their own enzymes, as they do not have direct access to the cell's nucleus. This allows them to independently replicate their genetic material in the cytoplasm.

Explanation
This statement is true because DNA viruses do require a DNA-dependent RNA polymerase to transcribe their genes into mRNA. Unlike RNA viruses, which have their own RNA-dependent RNA polymerase, DNA viruses lack this enzyme and therefore rely on the host cell's DNA-dependent RNA polymerase to carry out transcription. This allows the viral DNA to be transcribed into mRNA, which can then be translated into viral proteins.

Explanation
The explanation for the given correct answer is that viruses that carry out transcription in the cytoplasm, except for plus-strand RNA viruses, have the transcriptase enzyme present in the virion. This allows for immediate availability of the enzyme to transcribe the virus genome upon infecting a cell. This is important because transcription is a crucial step in the replication and survival of the virus within the host cell. Therefore, the statement is true.

Explanation
Retroviruses and pararetroviruses both use reverse transcriptases to perform reverse transcription. Reverse transcription is the process of converting RNA into DNA, which is then integrated into the host cell's genome. This is a characteristic feature of retroviruses and pararetroviruses, making the statement true.

Explanation
Many viruses that replicate in the cytoplasm have their own capping and methylating enzymes. This includes poxviruses, reoviruses, and coronaviruses. These enzymes are important for the viral replication process as they modify the viral mRNA, allowing it to evade host immune responses and ensuring efficient translation of viral proteins. Therefore, the correct answer is "All of the above" as all three types of viruses mentioned encode their own capping and methylating enzymes.

Explanation
The given statement is true. Hepadnaviruses, which are a type of DNA virus that infects mammals, use the sequence TATAAA as polyadenylation signals. Polyadenylation is a process in which a string of adenine nucleotides, known as a poly(A) tail, is added to the end of mRNA molecules. This modification is important for stability and proper functioning of mRNA. In hepadnaviruses, the TATAAA sequence serves as a recognition signal for the addition of the poly(A) tail.

Explanation
The statement is true because the first evidence of split genes was indeed reported in 1977 after studies with adenoviruses. This discovery revolutionized our understanding of gene structure and expression, revealing that genes are composed of exons and introns. Exons are the coding regions of genes that are expressed, while introns are non-coding regions that are spliced out during the process of gene expression. This finding had significant implications for our understanding of genetic regulation and paved the way for further research in molecular biology.

Explanation
The given statement is false because Sendai virus does not use AUG as the initiation codon for one of its genes. The initiation codon AUG is typically used by most organisms, including viruses, to start protein synthesis. However, some viruses, like Sendai virus, may use alternative initiation codons such as GUG or UUG. Therefore, the statement is incorrect.

Explanation
IRESs are indeed present in a number of RNA viruses, including hepatitis C virus and the picornaviruses. These internal ribosome entry sites allow for cap-independent translation initiation, which is crucial for the efficient translation of viral proteins. This mechanism allows the virus to bypass the host cell's normal translation machinery and ensure the production of viral proteins even under unfavorable conditions. Therefore, the statement is true.

Explanation
Most eukaryotic cell and virus mRNAs have one ORF, which stands for Open Reading Frame. An ORF is a sequence of DNA or RNA that can be translated into a protein. However, there are certain virus mRNAs that have two or more ORFs, meaning they can produce multiple proteins from a single mRNA molecule. This allows viruses to maximize their coding capacity and produce different proteins that are necessary for their replication and survival. Therefore, the statement "Most eukaryotic cell and virus mRNAs have one ORF, but there are a number of virus mRNAs that have two or more ORFs" is true.

Explanation
Some virus glycoproteins, like the rotavirus protein NSP4, are nonstructural proteins. This means that they do not play a role in the structure or replication of the virus. Instead, they may have other functions, such as aiding in viral entry into host cells or modulating the host immune response. Therefore, the statement that a few virus glycoproteins are nonstructural proteins, like NSP4, is true.

Explanation
This statement is true because viruses are intracellular parasites that rely on the host cell's machinery to replicate and produce proteins. After infecting a host cell, the virus's genetic material is transcribed into mRNA in the nucleus. This mRNA is then transported out of the nucleus and into the cytoplasm, where it can be translated into viral proteins. Additionally, some virus proteins may be transported back into the nucleus for various purposes, such as modifying the host cell's environment to favor viral replication. Therefore, both virus mRNAs and proteins can be transported between the nucleus and cytoplasm.

Explanation
Progeny virions, which are newly formed viral particles, have the ability to bud from either the plasma membrane or the nuclear envelope of infected cells. This means that they can be released from the cell by budding off from these two different locations. This process allows the virus to spread and infect other cells. Therefore, the statement that progeny virions may bud from the plasma membrane or the nuclear envelope is true.

Explanation
Enrique Rodriguez-Boulan and David Sabatini did not discover that vesicular stomatitis virus buds from the apical surface and influenza virus buds from the basolateral surface in 1978. Therefore, the statement is false.

Explanation
The statement is true because a nuclear localization signal (NLS) consisting of the amino acid sequence PKKKRKV was indeed first identified in a simian virus 40 protein called large T antigen. This NLS is responsible for targeting proteins to the nucleus of a cell.

Explanation
The Rev protein of HIV-1 contains both a nuclear localization signal and a nuclear export signal, allowing it to shuttle between the nucleus and the cytoplasm. This ability is crucial for the proper functioning of the Rev protein, as it is responsible for transporting unspliced viral RNA from the nucleus to the cytoplasm for translation and assembly of new viral particles. Thus, the statement is true.

Explanation
Introns are non-coding regions of DNA that are present in eukaryotic organisms, such as plants and animals. They are typically removed during the process of gene expression. Bacteria and their viruses, which are prokaryotic organisms, do not have introns in their genes. Therefore, the statement that introns are rarely present in the genes of bacteria and their viruses is true.

Explanation
The statement is false because while eukaryotic mRNAs are capped at the 5' end and polyadenylated at the 3' end, bacterial mRNAs do not have these modifications. Instead, bacterial mRNAs have different mechanisms to initiate translation and stabilize the mRNA molecule.

Explanation
Some phages have overlapping genes, meaning that the coding sequences of two or more genes overlap with each other. In these cases, the translation of these genes can occur in different ways. One way is by reading through a stop codon, which means that the ribosome continues translating the mRNA even after encountering a stop signal. Another way is through ribosomal frameshifting, where the ribosome shifts its reading frame to allow for the translation of a different gene. Therefore, the statement is true.

Explanation
If the virus replicates in the nucleus, it means that it needs to access the cellular machinery present in the nucleus to replicate its genetic material and produce new virus particles. This requires the transport of virus proteins into the nucleus, as these proteins are responsible for facilitating the replication process. Therefore, it is likely that most, if not all, of the virus proteins need to be transported into the nucleus for successful replication. Hence, the statement is true.

Explanation
Many viruses, including rhabdoviruses, have proteins that become phosphorylated. Phosphorylation is a process in which a phosphate group is added to a protein, often resulting in changes to its structure or function. This modification is important for various viral processes, such as viral replication, assembly, and interaction with host cells. Therefore, the statement that many structural and non-structural virus proteins become phosphorylated, including the phosphoproteins of rhabdoviruses, is true.