Podcast
Questions and Answers
Why must the repair process precede mRNA synthesis?
Why must the repair process precede mRNA synthesis?
- The repair process enhances mRNA stability.
- The repair process is not necessary for mRNA synthesis.
- Host RNA polymerase can only work with single-stranded RNA.
- Host RNA polymerase can only transcribe fully double-stranded DNA. (correct)
What is produced from an RNA template by a virus-encoded enzyme?
What is produced from an RNA template by a virus-encoded enzyme?
- Double-stranded RNA
- Single-stranded DNA (correct)
- Circular RNA
- Protein
Which of the following viral families is recognized to contain ssDNA genomes?
Which of the following viral families is recognized to contain ssDNA genomes?
- Adenoviridae
- Circoviridae (correct)
- Poxviridae
- Herpesviridae
What type of genome must be repaired before entering the replication cycle?
What type of genome must be repaired before entering the replication cycle?
What common feature is found in the structure of dsDNA viral genomes?
What common feature is found in the structure of dsDNA viral genomes?
Which statement about the replication cycle of some viral genomes is true?
Which statement about the replication cycle of some viral genomes is true?
What characterizes the viral families with dsDNA genomes in terms of size?
What characterizes the viral families with dsDNA genomes in terms of size?
Which type of enzyme is responsible for synthesizing single-stranded DNA from RNA?
Which type of enzyme is responsible for synthesizing single-stranded DNA from RNA?
Which of the following families include viruses that infect vertebrates?
Which of the following families include viruses that infect vertebrates?
What is the first step in the replication process of (+) strand RNA genomes?
What is the first step in the replication process of (+) strand RNA genomes?
What do the (+) strand RNA genomes of viruses typically require for protein translation?
What do the (+) strand RNA genomes of viruses typically require for protein translation?
In the case of retroviruses, what is significant about their (+) strand RNA genome?
In the case of retroviruses, what is significant about their (+) strand RNA genome?
Which of the following virus families does NOT contain (+) strand RNA viruses?
Which of the following virus families does NOT contain (+) strand RNA viruses?
During the genome replication process, what is produced after the (−) strand is copied?
During the genome replication process, what is produced after the (−) strand is copied?
What unique feature distinguishes the genome of retroviruses from other (+) strand RNA viruses?
What unique feature distinguishes the genome of retroviruses from other (+) strand RNA viruses?
Which component is considered part of the structure of viral single-stranded (+) RNA genomes?
Which component is considered part of the structure of viral single-stranded (+) RNA genomes?
Which viruses were first found in aquatic vertebrates?
Which viruses were first found in aquatic vertebrates?
What are the two largest known viral genomes?
What are the two largest known viral genomes?
What is the genome size of anelloviruses?
What is the genome size of anelloviruses?
What is the significance of viral genome sequences?
What is the significance of viral genome sequences?
Which of the following is NOT true regarding viroids?
Which of the following is NOT true regarding viroids?
What does the phylogenetic diversity of fish viruses indicate?
What does the phylogenetic diversity of fish viruses indicate?
Which of the following statements regarding viral genome studies is accurate?
Which of the following statements regarding viral genome studies is accurate?
What is a characteristic of viroids compared to other viruses?
What is a characteristic of viroids compared to other viruses?
What does the genetic analysis of Pandoravirus salinus indicate about its genes?
What does the genetic analysis of Pandoravirus salinus indicate about its genes?
What conclusion can be made regarding the evolutionary lineage of viruses?
What conclusion can be made regarding the evolutionary lineage of viruses?
Which of the following represents a significant challenge in understanding the origin of viral genomes?
Which of the following represents a significant challenge in understanding the origin of viral genomes?
What type of genes are considered 'hallmark genes' in different viruses?
What type of genes are considered 'hallmark genes' in different viruses?
The discovery of ancient viral DNA in environmental samples provides evidence for what aspect of viral evolution?
The discovery of ancient viral DNA in environmental samples provides evidence for what aspect of viral evolution?
What is suggested about viral replication enzymes in relation to their origins?
What is suggested about viral replication enzymes in relation to their origins?
Why is the RNA-dependent RNA polymerase significant among viral proteins?
Why is the RNA-dependent RNA polymerase significant among viral proteins?
What process contributes to the diversity of capsid protein genes in viruses?
What process contributes to the diversity of capsid protein genes in viruses?
What is meant by the term 'wild type' in virology?
What is meant by the term 'wild type' in virology?
Which of the following best describes temperature-sensitive mutants?
Which of the following best describes temperature-sensitive mutants?
What characteristic is commonly sought after in viral mutants during screening?
What characteristic is commonly sought after in viral mutants during screening?
What is the difference between laboratory wild types and field isolates?
What is the difference between laboratory wild types and field isolates?
Which terms are commonly used by virologists to describe variations of a virus?
Which terms are commonly used by virologists to describe variations of a virus?
What does the term 'lethal mutations' refer to?
What does the term 'lethal mutations' refer to?
Which characteristic is NOT associated with silent mutations?
Which characteristic is NOT associated with silent mutations?
What does the term 'host range' refer to in virology?
What does the term 'host range' refer to in virology?
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Study Notes
Viral Genome Repair and Replication Strategies
- Host RNA polymerase can only transcribe fully double-stranded DNA (dsDNA).
- Gapped DNA genomes produced by some viruses require repair before mRNA synthesis.
- Viral genomes can enter the replication cycle directly or first necessitate the synthesis of essential viral gene products.
Types of Viral Genomes
-
Single-Stranded DNA (ssDNA):
- Thirteen families of ssDNA viruses identified, including Anelloviridae and Circoviridae.
-
Double-Stranded DNA (dsDNA):
- Includes families such as Polyomaviridae, Adenoviridae (30–50 kbp), Herpesviridae (120–240 kbp), and Poxviridae (130–375 kbp).
- Structures and expression processes vary across families.
RNA Virus Classification and Replication
-
+ Strand RNA Viruses:
- Families include Picornaviridae and Togaviridae.
- Preferentially translatable into proteins by host ribosomes.
- Replication occurs in two steps: copying the + strand into a full-length - strand, then back to + strand genomes.
-
Retroviruses:
- Defining trait includes converting the + strand RNA genome into a dsDNA intermediate via reverse transcriptase, a hallmark of Retroviridae.
Genome Size and Diversity
- The largest known viral genomes belong to Pandoravirus salinus and Pandoravirus dulcis, with 2.4 million and 1.9 million bases of dsDNA, respectively.
- Viroids represent the smallest known viral genomes, with lengths of 246 to 401 nucleotides and no coding capacity.
- Viiral genomes exhibit a wide range in sizes, impacting their evolutionary trajectories and adaptations.
Importance of Viral Genome Sequences
- Viral genome sequences are crucial for cataloging and classifying viruses.
- Partial genome sequences can assist in identifying responsible viruses during outbreaks and tracking their spread.
- Some viroid and anellovirus genomes indicate pollution in agricultural sectors, emphasizing their economic impact.
Origin of Viral Genomes
- No solid evidence of viral fossils complicates the understanding of the origins of viral genomes.
- Evidence suggests that viral replication enzymes may have originated from precellular self-replicating elements in ancient cells.
- Capsid proteins have been found to derive from unrelated genes, highlighting the complex evolutionary pathways of viruses.
Terminology and Concepts in Virology
- The term "wild type" refers to the natural strain from which mutants are derived, differentiated from laboratory adaptations.
- Viral strains are categorized based on genetic heritability and pathogenesis through terms such as "strains," "variants," and "mutants."
- Clinical isolates are distinct from laboratory wild types, as they originate from natural infections.
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