Viral Replication and Structure Overview

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Questions and Answers

Which RNA viruses replicate in the nucleus during certain stages of their lifecycle?

Retroviruses and Orthomyxoviruses (correct)

Picornaviruses and Flaviviruses

Coronaviruses and Astroviruses

Paramyxoviruses and Rhabdoviruses

What is the primary role of structural proteins in viral assembly?

To inhibit host immune responses

To transport viral RNA to the cell membrane

To assist in promoting cell division

To form the viral capsid and encapsidate the genome (correct)

Which group in the Baltimore Classification is characterized by replication of double-stranded DNA viruses?

Group 3

Group 1 (correct)

Group 2

Group 5

During the release of enveloped viruses, what mechanism do these viruses primarily use?

Budding through the cell membrane Signup and view all the answers

What is a key feature of positive-sense RNA viruses during replication?

They directly translate to form proteins Signup and view all the answers

What is the role of the host's DNA-dependent DNA polymerase in the replication of double-stranded DNA viruses?

It replicates the viral genome into new viral DNA strands Signup and view all the answers

In what compartment does assembly of nucleocapsids generally occur for most RNA viruses?

In the cytoplasm Signup and view all the answers

Which of the following best describes the viral replication process?

It combines both protein synthesis and the copying of genetic material. Signup and view all the answers

Which protein allows the influenza virus to attach to host cells?

Hemagglutinin (HA) Signup and view all the answers

What mechanism do enveloped viruses like HIV utilize to enter host cells?

Direct fusion Signup and view all the answers

What is the primary site of nucleic acid synthesis for most DNA viruses?

Nucleus Signup and view all the answers

What process leads to the loss of virion infectivity in viral replication?

Uncoating Signup and view all the answers

Which of the following viruses utilizes receptor-mediated endocytosis as a method of entry?

Adenovirus Signup and view all the answers

What is the function of the M2 ion channel in the influenza virus?

Enables uncoating Signup and view all the answers

In the context of Baltimore classification, which type of virus does NOT replicate in the nucleus?

Pox viruses Signup and view all the answers

Which mechanism is used by viruses to release their newly-formed virions from host cells?

Budding Signup and view all the answers

What is the primary genetic material that RNA viruses utilize for replication?

Single-stranded RNA Signup and view all the answers

Which step follows uncoating in the viral replication process?

Synthesis Signup and view all the answers

What characterizes the assembly step in viral replication?

New virions are formed from replicated components Signup and view all the answers

What does the Baltimore classification system categorize viruses by?

Genetic material and replication strategy Signup and view all the answers

Which of the following describes a common release mechanism of viruses?

Viruses are released through cell lysis or budding Signup and view all the answers

In the context of viral attachment, what role do viral surface proteins play?

They bind to specific receptors on the host cell Signup and view all the answers

What is a defining feature of DNA viruses during their replication process?

They can integrate into the host cell's genome Signup and view all the answers

Which of the following viruses is categorized as an enveloped virus?

HIV Signup and view all the answers

Study Notes

Viral Replication Overview

Viral replication is a complex process encompassing multiple steps
The fundamental steps of viral replication are: attachment (adsorption), penetration (entry), uncoating, synthesis (replication & protein production), assembly (maturation), and release (egress).

Basic Structure of Viruses

Components: genetic material (DNA or RNA, but not both), protein coat (capsid), envelope (some viruses), shapes and sizes (helical, icosahedral, complex).
Examples of enveloped viruses: HIV, influenza virus; examples of non-enveloped viruses: adenovirus, poliovirus.

Viral Classification

Based on genetic material: DNA viruses, RNA viruses.
Based on replication strategy: different classifications exist (Baltimore Classification).

Viral Replication Steps: Step 1 - Attachment (Adsorption)

Mechanism: viral surface proteins bind to specific receptors on the host cell membrane.
Receptors are proteins, carbohydrates, or parts of the lipid bilayer.
Specificity: determines host range and tissue tropism (which cells the virus can infect).
Examples: HIV's gp120 binds to CD4 receptors; influenza virus' hemagglutinin binds to sialic acid.

Viral Replication Steps: Step 2 - Penetration (Entry)

Mechanisms: direct fusion (enveloped viruses); receptor-mediated endocytosis (enveloped and non-enveloped viruses).
Direct fusion: viral envelope merges with the host cell membrane.
Receptor-mediated endocytosis: cell membrane invaginates to engulf the virus.

Viral Replication Steps: Step 3 - Uncoating

Definition: separation of the capsid from the viral genome, resulting in loss of infectivity.
Mechanisms: lysosomal enzymes (degrade capsid proteins) and conformational changes (triggered by pH shifts).
Example: influenza virus' uncoating facilitated by M2 ion channel.

Viral Replication Steps: Step 4 - Synthesis: Replication and Protein Production

Viral nucleic acid synthesis begins after uncoating.
Location varies: most DNA viruses replicate in the nucleus, except Pox and Herpes viruses which replicate in cytoplasm. All RNA viruses replicate in the cytoplasm, except Orthomyxoviruses and retroviruses, which use nucleus at certain stages.

Viral Replication Steps: Step 5 - Assembly (Maturation)

Process: assembly of viral genome and proteins into new virions.
Locations: nucleocapsid assembly generally in the cytoplasm (for RNA viruses) or nucleus (for DNA viruses).

Viral Replication Steps: Step 6 - Release

Process: cell breaks open to release the virus.
Enveloped viruses: acquire their envelope by budding through the cell membrane.

Negative vs. Positive Sense Strand of DNA and RNA

Negative strand DNA/RNA must be copied (transcribed/reverse transcribed) into a complementary form (plus strand), before mRNA synthesis can start.
Positive strand DNA/RNA can be used directly as mRNA.

Baltimore Classification

A system for classifying viruses based on their genetic material, and how mRNA is made.
Different groups (1-7) have various genetic material and steps of synthesis. Each virus group replicates slightly differently.

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Description

This quiz covers the essential processes of viral replication, including the steps involved from attachment to release. It also explores the basic structure of viruses and their classification, providing examples of both enveloped and non-enveloped viruses. Test your knowledge on viral biology and the mechanisms behind these fascinating pathogens.