Problem 4 What features distinguish the se... [FREE SOLUTION]

Chapter 33: Problem 4

What features distinguish the seven major categories of viruses?

Short Answer

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The seven major categories of viruses are distinguished based on their genetic material and replication strategies: 1. Double-stranded DNA viruses (dsDNA) have a double-stranded DNA genome and replicate in the host cell nucleus. 2. Single-stranded DNA viruses (ssDNA) have a single-stranded DNA genome and require host cell enzymes for replication. 3. Double-stranded RNA viruses (dsRNA) have a double-stranded RNA genome and use an RNA-dependent RNA polymerase (RdRP) for replication. 4. Positive-sense single-stranded RNA viruses (+ssRNA) have a single-stranded RNA genome that functions as mRNA and can be directly translated into protein. 5. Negative-sense single-stranded RNA viruses (-ssRNA) have a genome complementary to mRNA and require an RdRP to synthesize positive-sense RNA for protein translation. 6. Retroviruses (ssRNA-RT) have a single-stranded RNA genome and use reverse transcriptase (RT) to synthesize a DNA copy for integration into the host cell's DNA. 7. Double-stranded DNA viruses with reverse transcriptase (dsDNA-RT) have a double-stranded DNA genome and use RT to synthesize their mRNA via an RNA intermediate.

Step by step solution

Listing the Seven Major Categories of Viruses

The seven major categories of viruses are as follows: 1. Double-stranded DNA viruses (dsDNA) 2. Single-stranded DNA viruses (ssDNA) 3. Double-stranded RNA viruses (dsRNA) 4. Positive-sense single-stranded RNA viruses (+ssRNA) 5. Negative-sense single-stranded RNA viruses (-ssRNA) 6. Retroviruses (ssRNA-RT) 7. Double-stranded DNA viruses with reverse transcriptase (dsDNA-RT)

Describing Characteristics of Double-stranded DNA Viruses (dsDNA)

Double-stranded DNA viruses have a genome consisting of double-stranded DNA. These viruses replicate inside the host cell nucleus using the host cell's replication machinery. Examples of dsDNA viruses include herpesviruses, papillomaviruses, and adenoviruses.

Describing Characteristics of Single-stranded DNA Viruses (ssDNA)

Single-stranded DNA viruses have a genome consisting of single-stranded DNA. These viruses also replicate inside the host cell nucleus but require host cell enzymes to synthesize a complementary DNA strand before replication can occur. Examples of ssDNA viruses include parvoviruses and circoviruses.

Describing Characteristics of Double-stranded RNA Viruses (dsRNA)

Double-stranded RNA viruses have a genome consisting of double-stranded RNA. Their replication strategy involves synthesizing mRNA from the viral dsRNA using an RNA-dependent RNA polymerase (RdRP) enzyme. Examples of dsRNA viruses include rotaviruses and reoviruses.

Describing Characteristics of Positive-sense Single-stranded RNA Viruses (+ssRNA)

Positive-sense single-stranded RNA viruses have a genome consisting of single-stranded RNA that can be directly translated into protein by the host cell ribosomes. The viral genome functions as mRNA. Examples of +ssRNA viruses include picornaviruses, flaviviruses, and coronaviruses.

Describing Characteristics of Negative-sense Single-stranded RNA Viruses (-ssRNA)

Negative-sense single-stranded RNA viruses have a genome with an RNA sequence complementary to the mRNA. Therefore, these viruses must carry an RNA-dependent RNA polymerase (RdRP) to synthesize positive-sense RNA, which can then be translated into proteins. Examples of -ssRNA viruses include influenza viruses, paramyxoviruses, and rhabdoviruses.

Describing Characteristics of Retroviruses (ssRNA-RT)

Retroviruses have a genome consisting of single-stranded RNA, and what makes them unique is the presence of reverse transcriptase enzyme (RT). These viruses replicate by synthesizing a DNA copy of their RNA genome, which is then integrated into the host cell's DNA. Examples of retroviruses include human immunodeficiency virus (HIV) and some tumor viruses.

Describing Characteristics of Double-stranded DNA Viruses with Reverse Transcriptase (dsDNA-RT)

Double-stranded DNA viruses with reverse transcriptase have a genome consisting of double-stranded DNA, but they use reverse transcriptase enzyme (RT) to synthesize their mRNA. These viruses replicate their genomes via an RNA intermediate, which is reverse-transcribed back into DNA. An example of a dsDNA-RT virus is the hepatitis B virus.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Double-Stranded DNA Viruses

Double-stranded DNA (dsDNA) viruses possess a genome structured as two complementary DNA strands that mirror each other, much like the two sides of a zipper. This construction allows them to use the host's cellular machinery to replicate, as their DNA can integrate smoothly into the host's genome.

In the cell nucleus, these viruses can craft their own 'blueprints' for new viral components by harnessing the host cell's replication systems. Think of it like a stealthy invader that slips into a factory and starts producing its own goods using the factory's equipment. Noteworthy members of this group include the well-known herpes viruses, which cause various diseases from cold sores to chickenpox, and the human papillomaviruses responsible for warts and, more critically, cervical cancer.

Single-Stranded RNA Viruses

Single-stranded RNA (ssRNA) viruses carry their genetic material as RNA, rather than DNA, and they can be further divided into positive-sense (+ssRNA) and negative-sense (-ssRNA) viruses.

Positive-Sense Single-Stranded RNA Viruses

These are the 'ready-to-go' viruses. Their RNA can directly serve as a template for protein synthesis immediately upon entering the host cell, similar to a plug-and-play device. Some of these viruses, like the ones that cause the common cold or the more severe hepatitis C, don't waste time before hijacking the host cell's machinery to begin making viral proteins.

Negative-Sense Single-Stranded RNA Viruses

On the other end, negative-sense ssRNA viruses come with a more roundabout approach. Their RNA is opposite to the mRNA needed for protein creation, meaning they must first craft a complementary strand. This can be likened to bringing a mirror-image instruction manual that needs to be translated before use, a method characteristic of the infamous influenza and rabies viruses. To achieve this, these cunning pathogens carry their own special enzyme, RNA-dependent RNA polymerase (RdRP), to kickstart the process inside the host cell.

Reverse Transcriptase

Reverse transcriptase is an enzyme with a 'backward' function, hence the name. Within certain viruses, like retroviruses, it defies the normal flow of genetic information by transcribing RNA back into DNA.

This remarkable ability allows retroviruses, including the widely known HIV (human immunodeficiency virus), to embed their genetic code into the DNA of the host cells they infect. The result is essentially a genetic 'sleeper cell' that can activate and produce new viruses at a later time.

Moreover, some unique dsDNA viruses also utilize reverse transcriptase, not to assimilate into the host genome, but to generate viral mRNA via an RNA intermediate. It's as if these viruses are bilingual, speaking both DNA and RNA fluently and using this skill to manipulate the host cell to produce viral proteins. The hepatitis B virus, for example, uses this enzyme to maintain its persistence in the infected organism, complicating treatment and vaccine development.

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What features distinguish the seven major categories of viruses?

Short Answer

Step by step solution

Listing the Seven Major Categories of Viruses

Describing Characteristics of Double-stranded DNA Viruses (dsDNA)

Describing Characteristics of Single-stranded DNA Viruses (ssDNA)

Describing Characteristics of Double-stranded RNA Viruses (dsRNA)

Describing Characteristics of Positive-sense Single-stranded RNA Viruses (+ssRNA)

Describing Characteristics of Negative-sense Single-stranded RNA Viruses (-ssRNA)

Describing Characteristics of Retroviruses (ssRNA-RT)

Describing Characteristics of Double-stranded DNA Viruses with Reverse Transcriptase (dsDNA-RT)

Key Concepts

Double-Stranded DNA Viruses

Single-Stranded RNA Viruses

Positive-Sense Single-Stranded RNA Viruses

Negative-Sense Single-Stranded RNA Viruses

Reverse Transcriptase

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