Introduction to Medical Virology: Understanding Viruses

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Questions and Answers

Which type of RNA viruses have to synthesize mRNA to the host cell?

(+) polarity RNA viruses

Retroviridae viruses

(-) polarity RNA viruses (correct)

Influenza viruses

Where do RNA viruses assemble?

Mitochondria

Nucleus

Endoplasmic reticulum

Cytoplasm (correct)

In which stage the viral structure components, called capsid and peplomers are synthesized.

Exit from the Cell

Synthesis of late proteins (correct)

Assembly

Viral genome synthesis

How do non-enveloped viruses leave the cell?

By disrupting the cytoplasm membrane (C) Signup and view all the answers

What are viruses that use their own RNA as mRNA called?

(+) polarity RNA viruses (D) Signup and view all the answers

Where do protein building blocks of DNA viruses migrate to for recovery?

Nucleus (D) Signup and view all the answers

In which stage of replication does the synthesis of replication enzymes occur?

Viral genome synthesis (B) Signup and view all the answers

What is the term for the stage in which viral structure components, called capsid and peplomers, are synthesized?

<ul> <li>Synthesis of late proteins (C)</li> </ul> Signup and view all the answers

How do enveloped viruses leave the cell?

<ul> <li>By budding from various host membranes (A)</li> </ul> Signup and view all the answers

Where do DNA virus recovery occur?

<ul> <li>Nucleus (A)</li> </ul> Signup and view all the answers

Which of the following best describes a virus?

An acellular organism that depends on the host's metabolism (C) Signup and view all the answers

What is the primary reason why viruses must live in a host cell?

To replicate using the host's metabolism (C) Signup and view all the answers

What is the main characteristic of viruses in terms of their metabolic activity outside living cells?

They are completely inert outside living cells (A) Signup and view all the answers

What is the key factor affecting the diversity of hosts for viruses?

The ability of the virus to enter the host cell (D) Signup and view all the answers

Which statement best describes the relationship between viruses and host cells?

Viruses show a high degree of specificity to host cells (B) Signup and view all the answers

What is the nature of a virus's dependence on the host's metabolism?

Complete dependence for replication and energy (C) Signup and view all the answers

Why are viruses classified as obligate intracellular parasites?

As they are completely dependent on cellular metabolism and energy (C) Signup and view all the answers

What determines the ability of a virus to enter a host cell?

The presence of specific entry receptors on the host cell membrane (A) Signup and view all the answers

What is the primary reason why viruses replicate inside a host cell?

To ensure viral spread and infection within the host (B) Signup and view all the answers

What distinguishes viruses from cellular microorganisms?

The lack of their own metabolism and energy production (B) Signup and view all the answers

Which structure of the virus allows naked viruses to attach to the host cell?

Capsid (B) Signup and view all the answers

What is the main function of a virion?

To transport the viral genome into the host cell (D) Signup and view all the answers

Which type of virus has a segmented genome?

RNA viruses (A) Signup and view all the answers

What determines the length of the nucleocapsid in viruses with helical symmetry?

Length of the nucleic acid (C) Signup and view all the answers

Which type of symmetry is exhibited by large viruses with a diameter of 200-300 nm?

Complex symmetry (C) Signup and view all the answers

Where does the envelope of enveloped viruses originate from?

All of the above (D) Signup and view all the answers

What is the main structure that forms the envelope of enveloped viruses?

Lipid layer (B) Signup and view all the answers

Study Notes

RNA Viruses and mRNA Synthesis

Positive-sense RNA viruses synthesize mRNA directly for host translation.
Negative-sense RNA viruses must first be converted to mRNA before being translated by host ribosomes.

Virus Assembly and Components

RNA viruses typically assemble in the cytoplasm of host cells.
Capsid and peplomers are synthesized during the maturation stage of viral replication.

Virus Release Mechanisms

Non-enveloped viruses exit host cells via cell lysis, causing the cell to burst.
Enveloped viruses leave the host cell through budding, acquiring a portion of the host cell membrane as their envelope.

Viral RNA and Host Interaction

Viruses that utilize their own RNA as mRNA are classified as positive-sense RNA viruses.
Protein building blocks of DNA viruses migrate to the nucleus for recovery and assembly.

Stages of Viral Replication

Synthesis of replication enzymes occurs during the early phase of the viral replication cycle.
The term "maturation" refers to the stage where viral structure components, like capsid and peplomers, are synthesized.

Virus Characteristics and Host Dependency

Viruses are classified as obligate intracellular parasites due to their dependence on host cellular machinery for replication.
The primary reason for viral dependence on host cells is to harness cellular resources for energy and protein synthesis.

Viral Interaction with Host Cells

Viruses exhibit metabolic inactivity outside host cells, relying on hosts for metabolic functions.
The diversity of hosts for viruses is largely determined by the presence of specific receptor proteins on the host cell surface.

Viral Entry and Host Relationships

The ability of a virus to enter a host cell is dictated by the presence of specific receptors that the virus can attach to.
The primary reason viruses replicate within host cells is to ensure efficient production and assembly of new virions.

Distinction from Cellular Microorganisms

Viruses are distinguished from cellular microorganisms by their lack of cellular structure and independent metabolism.
The attachment structure of naked viruses is usually a protein that interacts with host cell receptors.

Structure and Symmetry of Viruses

A virion's main function is to deliver the viral genome into the host cell.
Segmented genome viruses include certain influenza viruses, characterized by multiple RNA segments.
The length of the nucleocapsid in helical viruses is determined by the length of the viral RNA and the encapsidation process.
Large viruses, around 200-300 nm in diameter, typically exhibit icosahedral symmetry.

Envelopes in Viruses

The envelope of enveloped viruses originates from the host cell membrane during the budding process.
The main structure that forms the envelope of enveloped viruses is composed of lipid bilayers and viral glycoproteins.

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Description

This quiz provides an introduction to medical virology, focusing on the nature of viruses, their genetic makeup, and their dependence on host cells for metabolism and replication. It covers the basic characteristics of viruses and their classification as acellular organisms.