Virus Genome and Structure Quiz

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Questions and Answers

What percentage of amino acid residues in the HIV-1 nucleocapsid protein are basic?

25 per cent

40 per cent

33 per cent

29 per cent (correct)

What is the primary function of a virion?

To protect and deliver the virus genome (correct)

To promote virus replication in host cells

To aid in the synthesis of viral proteins

To regulate immune responses in the host

What types of nucleic acid can a virus genome consist of?

Either RNA or DNA molecules (correct)

Only RNA molecules

Protein and lipid combinations

Only DNA molecules

Which feature is characteristic of the HIV-1 nucleocapsid protein?

It has two zinc fingers. Signup and view all the answers

Which type of viruses predominantly have segmented genomes?

ssRNA viruses Signup and view all the answers

Which enzyme would be used to determine if a virus has RNA as its genome?

Ribonuclease Signup and view all the answers

Which of the following is a bond that forms specifically in ssRNA?

G–U bonds Signup and view all the answers

In which type of virus is the genome typically packaged in one virion?

Influenza viruses Signup and view all the answers

How many categories of virus genomes are there based on nucleic acid type and strand configuration?

Four categories Signup and view all the answers

What component do many viruses have that aids in the entry into host cells?

Envelope Signup and view all the answers

Which of the following viruses has a segmented genome?

Influenza viruses Signup and view all the answers

What is a potential disadvantage of segmented genomes in viruses with segments packaged in separate virions?

New cells may become infected only if all genome segments enter the cell. Signup and view all the answers

What form is often seen in regions of secondary structure in single-stranded nucleic acids?

Stem-loops Signup and view all the answers

What is the role of the internal ribosome entry site in poliovirus RNA?

Binds cellular proteins to initiate translation Signup and view all the answers

What structure is primarily responsible for packaging the virus genome?

Capsid Signup and view all the answers

How do tertiary structures of nucleic acids impact virus replication?

They facilitate molecular interactions. Signup and view all the answers

Which of the following is not a category of virus genome?

Mixed-strand RNA Signup and view all the answers

What additional information does a virus genome carry beyond encoding virus proteins?

Signals for gene expression control Signup and view all the answers

What is a characteristic structure that can form due to intramolecular base pairing in ssRNA?

Pseudoknots Signup and view all the answers

What is one benefit of having a segmented genome for a virus?

Possibility of new gene combinations. Signup and view all the answers

What distinguishes a double-stranded RNA virus from other types?

It consists of two RNA strands Signup and view all the answers

What is the length of the largest RNA genomes known, specifically those of coronaviruses?

33 kb Signup and view all the answers

Which characteristic is not associated with the nucleic-acid-binding proteins mentioned?

High molecular weight Signup and view all the answers

What type of bonding occurs in single-stranded DNA (ssDNA)?

G–C and A–T bonding Signup and view all the answers

Study Notes

Virus Genome Size

The largest known RNA genomes are those of some coronaviruses, which are 33 kb of ssRNA
Some viruses, such as the mimivirus, have larger genomes than the genomes of some simple cellular organisms
The smallest genomes of cellular organisms include some mycoplasmas

Secondary and Tertiary Structure

The viral genome stores additional information beyond just the genes to be expressed
This information may be contained in the nucleotide sequences, or in the structures created by intramolecular base pairing in single-stranded genomes
Secondary structures are formed by intramolecular base pairing, which results in regions like stemloops and bulges
Tertiary structures are formed when regions of secondary structure in single-stranded nucleic acids fold into specific shapes
Many of these tertiary structures are important in molecular interactions during virus replication, such as the 5' end of poliovirus RNA, which contains an internal ribosome entry site for binding of proteins to initiate translation
Most proteins associated with virus genomes are virus-coded, such as the HIV-1 nucleocapsid protein, which coats the virus RNA.

Protein Characteristics

Besides being basic, nucleic-acid-binding proteins may contain other characteristics, like zinc fingers
In some viruses, such as tobacco mosaic virus, the protein coating the genome constitutes the capsid of the virion

Segmented Genomes

Most virus genomes consist of a single molecule of nucleic acid
Some viruses have segmented genomes, where their genes are encoded in two or more nucleic acid molecules
Segmented genomes are more common among RNA viruses than DNA viruses
Examples of RNA viruses with segmented genomes include the influenza viruses, which package their segments in one virion, and brome mosaic virus, which packages the segments in separate virions
Most dsRNA viruses, such as members of the family Reoviridae, have segmented genomes
Segmented genomes provide the potential for new gene combinations and rapid evolution, but require that all genome segments enter a cell for infection to occur

Virus Structure

Outside of a host cell, viruses survive as virus particles, also known as virions
Virions act as gene delivery systems, protecting the viral genome and aiding its entry into a host cell
The viral genome is packaged within a protein structure called a capsid
Many viruses also have a lipid component, forming an envelope, which typically contains proteins that aid entry into host cells
Some viruses form protective protein occlusion bodies around their virions

Virus Genome Composition

Every virion contains the virus genome in the form of one or more molecules of nucleic acid
For any one virus, the genome is composed of either RNA or DNA
If a new virus is isolated, its susceptibility to a ribonuclease and a deoxyribonuclease can be tested to determine if it is an RNA or DNA virus
Each nucleic acid molecule is either single-stranded (ss) or double-stranded (ds), yielding four categories of virus genome: dsDNA, ssDNA, dsRNA, ssRNA

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Description

Test your knowledge about virus genomes, focusing on RNA sizes and structural formations. This quiz covers topics like the largest RNA genomes, secondary and tertiary structures, and their roles in virus replication. Delve into the fascinating world of viral genetics and its complexities.