Positive Strand RNA Viruses: Picornaviruses Overview
45 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the structure of picornaviruses?

  • Enveloped helical capsid with a diameter of ~50 nm
  • Complex cylindrical structure with a diameter of ~100 nm
  • Naked icosahedral capsid with a diameter of ~30 nm (correct)
  • Naked filamentous capsid with a diameter of ~20 nm

What is the primary mode of transmission for viruses in the Flavivirus genus?

  • Via contaminated water supplies
  • Transmitted by arthropods (correct)
  • Through foodborne routes
  • Direct contact with infected individuals

Which protein remains buried within the capsid of picornaviruses?

  • VP1
  • VP4 (correct)
  • VP3
  • VP2

What type of genetic material do picornaviruses have?

<p>Single-stranded RNA with positive sense (B)</p> Signup and view all the answers

Which of the following statements about the Pestivirus genus is accurate?

<p>It causes economically important diseases in livestock. (A)</p> Signup and view all the answers

Which virus is contained within the Hepacivirus genus?

<p>Hepatitis C virus (B)</p> Signup and view all the answers

Which of the following diseases is NOT caused by picornaviruses?

<p>Influenza (B)</p> Signup and view all the answers

How many copies of M and E proteins are found in a flavivirus virion?

<p>180 copies each (D)</p> Signup and view all the answers

What is unique about the 5’ and 3’ ends of the picornavirus RNA genome?

<p>The 5’ end has a viral protein VPg instead of a 5’ cap (A)</p> Signup and view all the answers

What structural feature do mature flavivirus particles possess?

<p>They have a golf ball-like appearance. (C)</p> Signup and view all the answers

What is the primary role of eIF-4F complex in the translation process of cellular RNAs?

<p>It binds to the 5’ end of RNA and recruits ribosomal subunits. (D)</p> Signup and view all the answers

What impact does proteolytic cleavage of eIF-4G have on the host cell during picornavirus infection?

<p>It abolishes cap-dependent translation. (D)</p> Signup and view all the answers

How does the 40S ribosomal subunit initiate translation after scanning the mRNA?

<p>By finding the initiator codon (AUG) and assembling the 80S ribosome. (B)</p> Signup and view all the answers

What is a consequence of failing to properly recruit eIF-4E during picornavirus infection?

<p>Failure to initiate translation of cellular mRNA. (D)</p> Signup and view all the answers

Which of the following best describes how picornavirus proteins are produced?

<p>As a single precursor polyprotein that is cleaved by viral proteinases. (D)</p> Signup and view all the answers

What characterizes the genome of flaviviruses?

<p>It is a linear single-stranded RNA capped at the 5' end. (C)</p> Signup and view all the answers

How are the proteins of flaviviruses generated from their genome?

<p>As a long polyprotein followed by proteolytic cleavage. (C)</p> Signup and view all the answers

Which of the following structural proteins is found in the mature virion of flaviviruses?

<p>Three structural proteins. (B)</p> Signup and view all the answers

What is unique about the E protein in flaviviruses?

<p>It creates a hydrophobic fusion peptide protected by neighboring E proteins. (A)</p> Signup and view all the answers

What role do viral and cellular proteases play in flavivirus replication?

<p>They act to cleave the polyprotein into mature proteins. (C)</p> Signup and view all the answers

What mechanism assists in the entry of flaviviruses into host cells?

<p>Endocytosis within clathrin-coated vesicles. (D)</p> Signup and view all the answers

What is the consequence of antibody-dependent enhancement (ADE) in flavivirus infections?

<p>It can lead to more severe disease manifestations. (C)</p> Signup and view all the answers

Which characteristic distinguishes flaviviruses from togaviruses?

<p>Differences in genome structure and organization. (D)</p> Signup and view all the answers

What is the primary role of proteinases in the Picornavirus life cycle?

<p>To cleave the polyprotein into functional proteins (A)</p> Signup and view all the answers

What is the function of the internal ribosome entry site (IRES) in Picornaviruses?

<p>To allow translation initiation without a 5’ cap (D)</p> Signup and view all the answers

Which proteins are primarily encoded by the P1 region of the Picornavirus genome?

<p>Structural proteins (D)</p> Signup and view all the answers

What characterizes the structure of the IRES elements in Picornaviruses?

<p>They contain pyrimidine rich tracts (C)</p> Signup and view all the answers

How do virions of Picornaviruses typically enter host cells?

<p>Through receptor-mediated endocytosis (C)</p> Signup and view all the answers

What structural feature allows Picornavirus virions to bind to cellular receptors?

<p>Loop regions or ‘canyons’ on their surface (A)</p> Signup and view all the answers

What is the composition of the VP1-4 proteins in Picornaviruses?

<p>A jelly roll structure composed of β-barrels (B)</p> Signup and view all the answers

What is the likely function of the pyrimidine-rich tract found in IRES elements?

<p>To initiate translation at the correct position (B)</p> Signup and view all the answers

What mechanism facilitates the entry of Flaviviruses into host cells?

<p>Endocytosis (D)</p> Signup and view all the answers

Which protein is cleaved to release the mature C protein after its synthesis?

<p>NS2B/NS3A (C)</p> Signup and view all the answers

What role does the prM protein play in the Flavivirus lifecycle?

<p>Protects E protein from premature changes (D)</p> Signup and view all the answers

During Flavivirus replication, what is produced in significantly larger amounts?

<p>Plus-strand RNA (A)</p> Signup and view all the answers

What is the function of the furin protease in the Togavirus lifecycle?

<p>Cleaves prM before virion release (C)</p> Signup and view all the answers

What type of RNA genome do Togaviruses possess?

<p>Linear single-stranded positive-sense RNA (B)</p> Signup and view all the answers

How many structural proteins are translated from Togavirus subgenomic mRNA?

<p>Five (A)</p> Signup and view all the answers

What component is crucial for the assembly of the Flavivirus at intracellular membranes?

<p>Endoplasmic reticulum (D)</p> Signup and view all the answers

What initiates the translation of the Flavivirus genome in the host cell?

<p>Ribosomes binding to a poly(A) tail (C)</p> Signup and view all the answers

What term describes the viral RNA replication process that results in new plus-strand RNA for various purposes?

<p>Asymmetrical replication (B)</p> Signup and view all the answers

What is the primary consequence of receptor-mediated endocytosis for Togaviruses?

<p>Release of viral RNA into the cytosol (B)</p> Signup and view all the answers

What characteristic feature do Togavirus particles exhibit?

<p>Icosahedral symmetry with spikes (D)</p> Signup and view all the answers

What type of signal sequence is involved in the synthesis of the capsid protein precursor in Flaviviruses?

<p>20 AA signal sequence (C)</p> Signup and view all the answers

What is a major public health concern related to Togaviruses?

<p>Transmission via mosquitoes (C)</p> Signup and view all the answers

Flashcards

Picornavirus structure

Small, non-enveloped RNA viruses with an icosahedral capsid.

Picornavirus genome

Single-stranded positive-sense RNA genome with a single large protein-coding region (ORF).

Picornavirus proteins

The virus contains 60 copies of VP1, VP2, VP3, and VP4 to form the capsid.

VPg protein function

A viral protein (VPg) covalently bound to the 5' end of RNA genome.

Signup and view all the flashcards

Picornavirus RNA Location

A portion of the genome consists of a 5' end of the RNA genome, and short 3' end.

Signup and view all the flashcards

Polyprotein Cleavage

Picornaviruses translate their genome as a single, large protein (polyprotein) which is then cut into smaller, functional proteins by viral proteases.

Signup and view all the flashcards

Picornavirus Proteases

These enzymes are responsible for cutting the polyprotein into individual proteins, crucial for the virus's replication and assembly.

Signup and view all the flashcards

P1 Protein

The P1 region of the polyprotein encodes structural proteins, which form the viral capsid.

Signup and view all the flashcards

P2 and P3 Proteins

These regions of the polyprotein encode non-structural proteins, which are involved in viral replication and other functions within the host cell.

Signup and view all the flashcards

IRES

An internal ribosome entry site allows the virus to initiate translation at an internal site on its genome, bypassing the need for a 5' cap.

Signup and view all the flashcards

IRES Structure

The IRES has complex secondary and tertiary structures that interact with cellular proteins, essential for its function.

Signup and view all the flashcards

Virion Attachment

Picornaviruses attach to host cells through 'canyons' or loop regions on their surface, using cellular receptors as entry points.

Signup and view all the flashcards

Virion Entry

After attachment, the virus can enter the cell either through pores in the membrane formed by capsid proteins or through receptor-mediated endocytosis.

Signup and view all the flashcards

Cap-dependent translation

The process by which eukaryotic cells use the 5' cap structure of mRNAs to initiate protein synthesis.

Signup and view all the flashcards

What are Flaviviruses?

Flaviviruses are a genus of RNA viruses that are transmitted by arthropods (insects). They cause several important human diseases, including dengue fever and Zika virus infection.

Signup and view all the flashcards

eIF-4F complex

A group of proteins (eIF-4A, eIF-4E, and eIF-4G) that bind to the 5' cap and recruit the small ribosomal subunit (40S) to the mRNA.

Signup and view all the flashcards

What are Pestiviruses?

Pestiviruses are a genus of RNA viruses that primarily infect animals, especially livestock like cattle and sheep. They are not transmitted by insects and do not infect humans.

Signup and view all the flashcards

What is Hepacivirus?

Hepacivirus is a genus of RNA viruses that contains only one species: Hepatitis C virus. It infects humans through blood contact, such as blood transfusions, shared needles, or sexual contact.

Signup and view all the flashcards

How do picornaviruses enter the cytoplasm?

Picornaviruses enter the cytoplasm by forming a channel in the cell membrane using VP4 and the hydrophobic N-terminal of VP1.

Signup and view all the flashcards

Flavivirus Virion Structure

The flavivirus virion is surrounded by an envelope. The envelope contains 180 copies of M and E proteins arranged with icosahedral symmetry. Immature virions have spikes, while mature ones have a golf ball-like appearance.

Signup and view all the flashcards

How does picornavirus infection affect translation?

Picornavirus infection blocks cap-dependent translation by cleaving eIF-4G and sequestering eIF-4E.

Signup and view all the flashcards

How is Flavivirus Structure Different in Immature vs. Mature?

Immature Flaviviruses have spikes on their surface due to prM-E heterodimers arranged perpendicularly to the surface bilayer. During maturation, the prM component is cleaved, resulting in a mature virion with a golf ball-like appearance.

Signup and view all the flashcards

Flavivirus Genome

Single-stranded, positive-sense RNA genome (~10-11 kb) with a 5' cap but no poly(A) tail.

Signup and view all the flashcards

Flavivirus Protein Synthesis

All genes are translated as a single polyprotein, which is then cleaved into individual proteins by proteases.

Signup and view all the flashcards

Flavivirus Structural Proteins

The three structural proteins are capsid (C), membrane (M), and envelope (E).

Signup and view all the flashcards

Flavivirus Non-structural Proteins

These seven proteins are involved in replication and other functions within the host cell.

Signup and view all the flashcards

Flavivirus Polyprotein Cleavage

Both viral and cellular proteases are required to cleave the polyprotein into individual proteins.

Signup and view all the flashcards

Flavivirus E Protein Function

The E protein mediates receptor binding and membrane fusion, allowing the virus to enter the host cell.

Signup and view all the flashcards

Flavivirus Entry Mechanism

Entry is usually through endocytosis within clathrin-coated vesicles.

Signup and view all the flashcards

Antibody-dependent Enhancement (ADE)

Antibodies can bind to the virus and enhance its entry into cells that have Fc receptors, potentially causing more severe disease.

Signup and view all the flashcards

Dengue Virus (DENV)

A type of flavivirus that causes dengue fever, a mosquito-borne illness characterized by high fever, headache, muscle and joint pain, and rash.

Signup and view all the flashcards

Flavivirus Entry

Flaviviruses enter host cells through endocytosis, a process where the cell membrane engulfs the virus and forms a vesicle.

Signup and view all the flashcards

Endocytosis

A cellular process where the cell membrane wraps around a particle, forming a vesicle that engulfs the particle and brings it into the cell.

Signup and view all the flashcards

Fusion-active State

A conformational change in the E protein, triggered by low pH, that allows the virus to fuse with the cell membrane.

Signup and view all the flashcards

Capsid Protein

A structural protein that forms the protective shell of the virus.

Signup and view all the flashcards

Signal Sequence

A short segment of amino acids that directs proteins to specific cellular locations.

Signup and view all the flashcards

PrM & E Proteins

Two structural proteins that associate with each other during viral assembly.

Signup and view all the flashcards

Furin Protease

An enzyme that cleaves the prM protein during viral maturation.

Signup and view all the flashcards

RNA Replicase

A complex of enzymes that replicates the viral RNA.

Signup and view all the flashcards

Plus-Strand RNA

The viral RNA that serves as the messenger RNA for protein synthesis.

Signup and view all the flashcards

Minus-Strand RNA

A complementary copy of the plus-strand RNA used as a template for making more plus-strand copies.

Signup and view all the flashcards

Viral Assembly

The process of assembling new virions within the host cell.

Signup and view all the flashcards

Study Notes

Positive Strand RNA Viruses

  • Picornaviruses, Flaviviruses, Togaviruses are positive strand RNA viruses.

Picornaviruses - Structure

  • Picornaviruses are small RNA genome viruses.
  • They have a naked icosahedral capsid (non-enveloped).
  • The diameter is approximately 30 nm.
  • Hundreds of viral species infect humans, mammals, birds, fish, and other organisms.
  • They cause diseases like hepatitis, myocarditis, the common cold, and polio.

Picornaviruses - Genome and Proteins

  • Picornaviruses bind to cellular receptors.
  • Mature virions have 60 copies of each of the following three to four proteins: VP1, VP2, VP3, and VP4.
  • Viral protein VPg is covalently bound to the 5' end of the RNA, instead of a 5' cap.
  • P1 encodes structural proteins.
  • P2 and P3 encode non-structural proteins.
  • The 5' non-coding region contains an internal ribosome entry site (IRES) that allows translation initiation.
  • This IRES has extensive secondary and tertiary structures that interact with other cell proteins.
  • The polyprotein is processed into individual proteins by viral proteinases.

Picornaviruses - Entry

  • Poliovirus RNA enters the cytoplasm after major rearrangement of VP4 and hydrophobic N-terminal VP1, creating a channel in the membrane.

Flaviviruses - Structure

  • Flaviviruses are spherical, enveloped particles about 50nm in diameter.
  • They have a spherical nucleocapsid with icosahedral symmetry.
  • They lack projections, having a "golf ball" appearance.
  • Surface glycoproteins are arranged with icosahedral symmetry.

Flaviviruses - Genome and Proteins

  • Flaviviruses have a linear, positive sense, single-stranded RNA genome (~10-11 kB).
  • It's capped at the 5' end and lacks a poly(A) tail at the 3' end.
  • All genes are translated as single polyproteins and cleaved into proteins, including one capsid protein (C), two envelope proteins (M and E), and seven non-structural proteins.

Flaviviruses - Attachment and Entry

  • No specific cellular receptor has been identified.
  • Entry occurs by endocytosis within clathrin-coated vesicles.

Togaviruses - Structure

  • Togaviruses are spherical, enveloped viruses about 70nm in diameter.
  • They have envelope projections (spikes) and icosahedral symmetry in both the nucleocapsid and in the envelope glycoproteins.

Togaviruses - Genome and Proteins

  • Togaviruses are positive-sense, single-stranded RNA viruses (9.7-11.8 kb).
  • They possess a 5' methylated cap and a 3' poly(A) tail (~70 nucleotides).
  • They have four non-structural proteins involved in RNA synthesis.
  • They have five structural proteins translated from subgenomic mRNAs: one capsid protein, three envelope proteins, and a small hydrophobic protein.

Togaviruses - Genome and Proteins

  • The translated genome initially creates a single polyprotein that's later cleaved by host and viral proteases.
  • The RNA is initially translated into P123, then further cleaved by proteases into non-structural proteins, then the RNA is further translated into structural proteins from a subgenomic mRNA.

Togaviruses - Assembly and Exit

  • Togavirus capsid proteins interact with cytoplasmic tails of envelope proteins.
  • Togaviruses exit the cell by budding.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

BIOC20 - Lecture 7: Picornaviruses, Flaviviruses, and Togaviruses PDF

Description

Explore the world of positive strand RNA viruses with a focus on Picornaviruses. Learn about their structure, genome, and how they interact with host cells. Understand the diseases they can cause and the significance of their proteins in viral life cycles.

More Like This

Picornaviruses: Structure and Genome
34 questions

Picornaviruses: Structure and Genome

ComfortableComprehension avatar
ComfortableComprehension
Picornaviruses: Structure and Genomic Information
12 questions

Picornaviruses: Structure and Genomic Information

ComfortableComprehension avatar
ComfortableComprehension
Enteroviruses and Picornavirus Family
20 questions

Enteroviruses and Picornavirus Family

FeatureRichDeciduousForest avatar
FeatureRichDeciduousForest
RNA Viruses in Virology
10 questions

RNA Viruses in Virology

CoherentLouisville avatar
CoherentLouisville
Use Quizgecko on...
Browser
Open
Browser
Browser