Viruses

Page 3: General Properties of Viruses

Characteristics of Viruses and Viroids

  • Nonliving particles that require living cells for reproduction

  • Composed of nucleic acid genomes

  • Tobacco Mosaic Virus (TMV) noted as the first virus discovered

  • Figure 19.1: Affected plant with TMV

Page 4: Hosts and Characteristics of Selected Viruses

Table 19.1 Overview

  • Virus or Group: Identifies various viruses and their characteristics.

  • Nucleic Acid Type: dsDNA or ssRNA

  • Genome Size: Expressed in kb (kilobases)

  • Example Viruses:

    • Phage (E. coli): Lytic or harmless in host

    • Tobacco Mosaic Virus (TMV): Causes leaf mottling

    • Herpes Simplex: Causes blisters

  • Effect on Host: Ranges from harmless to severe effects

Page 5: Properties of Viruses

Basic Structure and Diversity

  • Viruses are small infectious particles with nucleic acid and a protein coat

  • Over 4,000 different types exist

  • Variation in host ranges, structures, and genome compositions

Page 6: Differences Among Viruses

Key Differences

  • Host Range: Different species and cell types affected

  • Structural Features:

    • All have capsids, varying in shape

    • Envelopes derived from host membranes

  • Genome Variations:

    • DNA vs. RNA, single vs. double stranded, linear vs. circular

  • Examples of viruses affecting various body systems

Page 7: Viral Structures

Types of Virus Structures

  • Images illustrate structures:

    • a) Tobacco mosaic virus (helical, nonenveloped)

    • b) Adenovirus (polyhedral, nonenveloped)

    • c) Influenza virus (enveloped)

    • d) T4 bacteriophage (complex structure)

Page 9: Reproduction of Viruses

Nature of Viruses

  • Viruses are not considered alive

  • Not composed of cells

  • Unable to perform metabolism independently

  • Viral reproductive cycles vary among virus types

Page 10: Viral Reproductive Cycle

Steps in Reproduction

  1. Attachment

  2. Entry

  3. Integration

  4. Synthesis of Viral Components

  5. Viral Assembly

  6. Release

Page 11: Steps 1 and 2 - Attachment and Entry

Detailed Description

  • Attachment: Specific binding to cell surface molecules

  • Entry:

    • Bacteriophage: Injects DNA

    • HIV: Fusion with host membrane

    • Immediate expression of viral genes possible

Page 12: Step 3 - Integration

Integration Process

  • Viral gene for integrase facilitates integration

  • Prophage: Integration into bacterial DNA

  • HIV: Uses reverse transcriptase to convert RNA to DNA

Page 13: Step 4 - Synthesis of Viral Components

Synthesis Details

  • Host enzymes replicate phage DNA and transcribe genes to mRNA

  • In HIV: DNA is transcribed in the nucleus to produce viral RNA

Page 14: Steps 5 and 6 - Assembly and Release

Assembly Overview

  • Some viruses self-assemble; others require additional proteins

  • Release Mechanisms:

    • Phages lyse host cells

    • Enveloped viruses bud off from cells

Page 15: Latency in Bacteriophages

Latent Phases

  • Integration of viral genomes leads to inactive/prophage states

  • Host cell replication includes prophage

  • Lytic vs. Lysogenic Cycle: Understanding the differences

Page 16: Prophage Dynamics

Lifecycle Description

  • Overview of lytic and lysogenic cycles including infection and release mechanisms

Page 17: Latency in Human Viruses

Mechanisms of Latency

  • Virus integration into host genome can lead to dormancy

  • Examples: HIV, herpes simplex viruses

Page 18: Emerging Viruses

Characteristics of Emerging Viruses

  • Recently arisen or increased infectiousness

  • Typically results from mutations in existing viruses

  • Examples: Coronavirus, H1N1, Zika, HIV

Page 19: Overview of COVID-19

Coronavirus Information

  • SARS-CoV-2 causes COVID-19, identified as a pandemic

  • Symptoms include fever, cough, pneumonia

  • Statistics on global COVID-19 cases and deaths

Page 20: HIV and AIDS

Disease Transmission

  • Modes of HIV transmission: sexual contact, blood transfusion, mother to child

Page 21: AIDS Statistics

Key Data Points

  • Total AIDS-related deaths since 1981

  • Prevalence and incidence data for HIV

Page 22: Impact of AIDS on the Immune System

Effects on Immunity

  • Destruction of helper T cells significantly impacts immune function

  • Increased susceptibility to opportunistic infections

Page 23: Drugs for HIV

Treatment Advances

  • Decrease in AIDS-related death rates

  • New antiviral drugs inhibit virus proliferation

Page 24: Drug Strategies for HIV

Approach to Treatment

  • Binding virus proteins and blocking necessary proteases

  • Challenges: Avoiding binding to host proteins

  • Utilizing drug cocktails to reduce resistance