Question 1

Which of the following is NOT thought to be a mechanism by which viroids cause disease in their plant hosts?

Accepted Answer

E

Question 2

Which of the following is NOT a type of infectious RNA that can cause disease?

Accepted Answer

Prions are not RNA molecules but rather misfolded proteins that can cause disease in humans and animals. The other choices are all types of infectious RNA molecules that can cause disease.

Question 3

Which of the following describes the major difference between hepatitis delta virus (HDV)and the plant viroids and satellite RNAs?

Accepted Answer

The major difference between hepatitis delta virus (HDV) and plant viroids and satellite RNAs is that only the HDV genome encodes a protein. HDV encodes the hepatitis delta antigen, which is essential for its replication and assembly, whereas plant viroids and satellite RNAs do not encode any proteins.

Question 4

When studying the replication of viroids and hepatitis delta virus, which of the following allows scientists to distinguish which of the three cellular RNA polymerases is required?

Accepted Answer

The sensitivity of the RNA polymerase to the toxin a-amanitin is the best way to distinguish which of the three cellular RNA polymerases is required. Each of the three polymerases is sensitive or insensitive to a-amanitin. For example, RNA polymerase II is sensitive to a-amanitin, while RNA polymerase I and III are not. By testing the sensitivity of the RNA polymerase to a-amanitin, scientists can determine which polymerase is required for the replication of viroids and hepatitis delta virus.

Question 5

The deamination of an adenine residue in the genome of the hepatitis delta virus causes which of the following to occur?

Accepted Answer

Deamination of adenine converts it to hypoxanthine, which pairs with cytosine instead of thymine. This change can lead to a stop codon (TAA, TAG, TGA) being converted to a tryptophan codon (TGG) if the adenine is part of the stop codon sequence.

Question 6

Which of the following mechanisms is used to produce the two different forms of the delta antigen from the hepatitis delta virus?

Accepted Answer

The hepatitis delta virus uses RNA editing by deamination of a specific base in the genome to produce the two different forms of the delta antigen. This process involves the modification of an adenosine base to inosine, which changes the coding sequence of the mRNA.

Question 7

Which of the following describes the function of the large delta antigen, produced by hepatitis delta virus?

Accepted Answer

The large delta antigen is required to package the genome of the hepatitis delta virus into the hepatitis B virions.

Question 8

When the ribozyme activity in the avocado sunblotch viroid cleaves the RNA genome, which of the following describes the structure of the nucleotide on the 5' side of the cleavage?

Accepted Answer

The structure of the nucleotide on the 5' side of the cleavage site after ribozyme activity in the avocado sunblotch viroid cleaves the RNA genome is characterized by a 2', 3'-cyclic phosphate. This is a distinctive feature of RNA cleavage by certain ribozymes, where the cleavage mechanism involves the formation of a 2', 3'-cyclic phosphate end and a 5'-hydroxyl end.

Question 9

Which of the following is a major difference between the group A and the group B viroids?

Accepted Answer

Group A viroids have a self-cleaving RNA mechanism, while group B viroids do not. This is a major distinguishing feature between the two groups.

Question 10

Viroids encode a single protein which is used to package the RNA for transmission between hosts.

Accepted Answer

Viroids do not encode any proteins. They consist only of circular RNA molecules that can replicate and cause disease in plants. They are transmitted between hosts in a naked form, without the need for packaging proteins.

Question 11

The RNA polymerase that copies the genome of the avocado sunblotch viroid is highly sensitive to the toxin a-amanitin.

Accepted Answer

Avocado sunblotch viroid is a small, single-stranded RNA molecule that does not encode proteins and therefore does not require RNA polymerase. Therefore, the statement is false.

Question 12

Viroid RNA molecules have a high degree of base pairing throughout the molecule.

Accepted Answer

Viroid RNA molecules are short, circular, single-stranded RNA molecules that lack a protein coat. They have a high degree of base pairing, which helps to stabilize their structure and allows them to replicate efficiently by hijacking host cellular machinery.

Question 13

How do we differentiate between the positive and negative strands of a viroid genome?

Accepted Answer

The answer of How do we differentiate between the positive...

Question 14

Which of the following statements about the plant satellite RNAs is FALSE?

Accepted Answer

Satellite RNAs do not encode their own capsid protein. Instead, they rely on the capsid protein provided by the helper virus for encapsidation and transmission to new hosts.

Question 15

The typical structure of the genome of a viroid is described as?

Accepted Answer

Viroids have a circular single-stranded RNA genome with a length of 250-400 nucleotides.

Question 16

The formation of the antigenome template of hepatitis delta virus requires which of the following cellular enzymes?

Accepted Answer

The formation of the antigenome template of hepatitis delta virus requires RNA polymerase II, a cellular enzyme. This enzyme is crucial for the replication process of the virus, as it transcribes the viral RNA genome into a complementary antigenome, serving as a template for subsequent rounds of replication.

Question 17

Which of the following groups of organisms do viroids cause disease in?

Accepted Answer

Viroids are small, infectious RNA molecules that can cause disease in plants. They are not known to infect insects, mammals, algae, or paramecia.

Question 18

The ribozyme function found in virioids and hepatitis delta virus can be used to cleave exogenous RNA molecules.Which of the following is a requirement for the ribozyme to be recycled and cleave more than one substrate?

Accepted Answer

The ribozyme can be recycled and cleave more than one substrate if there is only a short region of complementarity between the target and the ribozyme. This allows the ribozyme to bind and cleave different substrates without being completely consumed or degraded, enabling it to be used repeatedly. A and E are incorrect because they relate to conditions that affect the activity or stability of the ribozyme or the substrate, but do not relate to its ability to be recycled. B is also incorrect because while stability of the ribozyme may be important for its function, it is not directly related to its ability to be recycled. D is incorrect because magnesium ions are often required for proper folding and activity of ribozymes, and their absence would likely decrease, rather than enhance, the ability of the ribozyme to recycle.

Question 19

What is surprising about the observation that a cellular RNA polymerase copies the viroid genome?

Accepted Answer

Viroids are RNA molecules and do not have a DNA template for transcription. Therefore, it is surprising that a cellular RNA polymerase copies the viroid genome, as RNA polymerases usually transcribe from a DNA template.

Answer: A and D
 RNA polymerases usually require a pre-existing RNA or DNA primer, but viroids do not have either of these. Additionally, RNA polymerases usually initiate synthesis from a promoter region of a DNA template, not from a protein primer. Therefore, it is surprising that a cellular RNA polymerase copies the viroid genome without a primer or promoter.

Question 20

How is the 3' end of the hepatitis delta virus mRNA formed?

Accepted Answer

The 3' end of the hepatitis delta virus mRNA is formed by cleavage and polyadenylation by cellular enzymes, similar to the processing of cellular mRNAs.

Quiz 31: Viroids and Hepatitis Delta Virus