CH 12: Virus Infection and Viral Genomes Overview

Virus

Noncellular particle with a genome and capsid.

Bacteriophages

Viruses that infect bacterial cells.

Virus-First Model

Ancient viruses predated cellular organisms.

Reduction Model

Viruses evolved from parasitic cells through genome reduction.

Escape Model

Viruses arose from cellular components that escaped.

Host Range

Specific group of host species a virus infects.

Transmission

Process of reaching and infecting new hosts.

Tissue Tropism

Range of tissue types a virus can infect.

Broad Tropism

Virus infects many tissue types.

Narrow Tropism

Virus infects specific tissue types.

Antiviral Agents

Chemicals designed to combat viral infections.

Viral Genomes

Composed of either DNA or RNA.

Baltimore Model

Classifies viruses based on genome type and structure.

Group I

Double-stranded DNA viruses.

Group II

Single-stranded DNA viruses.

Group III

Double-stranded RNA viruses.

Group IV

Single-stranded RNA viruses, directly translated.

Group V

Single-stranded RNA viruses, require complement synthesis.

Group VI

Retroviruses, RNA reverse-transcribing viruses.

Group VII

Pararetroviruses, DNA reverse-transcribing viruses.

Capsid

Protein package enclosing a viral genome.

Icosahedral Capsid

Radial symmetry, 20 triangular faces.

Filamentous Viruses

Helical symmetry, flexible filament structure.

Complex-Tailed Bacteriophages

Icosahedral head with a tail for injection.

Amorphous Viruses

No symmetrical form, flexible core wall.

Viral Envelope

Membrane derived from host cell structures.

Spike Proteins

Aid viral attachment during host cell infection.

Tegument Proteins

Expressed during infection, aid viral replication.

Viral Genome Size

Varies greatly; RNA can be very small.

Retroviruses

Small genomes maximize virion production efficiency.

Avian Leukosis Virus (ALV)

Has three protein-encoding genes: gag, pol, env.

Double-Stranded DNA Viruses

Large genomes encoding numerous cellular-like proteins.

Herpes Simplex Virus

152 kilobases, encodes over 70 gene products.

Viroids

Infectious agents with circular RNA genomes.

Hepatitis Delta Ribozyme

RNA portion that catalyzes its own cleavage.

Prions

Infectious proteins with no nucleic acid.

PrPC

Normal protein that misfolds into infectious form.

PrPSc

Abnormal prion form that aggregates and kills cells.

Creutzfeldt-Jakob Disease

Neurodegenerative disease caused by prions.

Lytic Lifecycle

Immediate viral replication producing many progeny.

Lysogenic Lifecycle

Viral DNA integrates into host DNA as prophage.

Adsorption

Virus binds to specific host cell receptors.

Penetration

Virus injects nucleic acid into host cell.

Replication

Host cell produces viral components.

Maturation

Assembly of new virus particles.

Release

Host cell lyses, releasing infectious particles.

Burst Size

Number of virus particles released per cell.

Multiplicity of Infection (MOI)

Every host cell infected by viruses.

Eclipse Period

Phase where viruses are undetectable in medium.

Rise Period

Phase where phage particles begin to appear.

Antigenic Drift

Accumulation of mutations evading host antibodies.

Human Papillomavirus (HPV)

Infects basal epithelial cells, can cause cancer.

Gardasil Vaccine

Prevents certain strains of HPV effectively.

Icosahedral viruses

Small viruses, twice ribosome size, non-enveloped.

ds-DNA

Double-stranded DNA, circular structure.

Base pairs

8,000 base pairs encode eight genes.

Open reading frames

Multiple frames allow overlapping gene expression.

HPV integration

HPV integrates into host genome, causing cancer.

Oncogenes

Genes that promote cancer development.

Influenza A virus

Orthomyxovirus causing respiratory infections.

Antigenic drift

Minor mutations in envelope proteins.

Antigenic shift

Major genetic reassortment from different strains.

Virion structure

Asymmetrical, amorphous, no fixed capsid.

RNA segments

Eight segments required for influenza infection.

Hemagglutinin (HA)

Protein involved in virus entry into cells.

Neuraminidase (NA)

Protein facilitating viral release from host cells.

Defective particles

Majority of influenza particles are non-infectious.

Virion production

Infected cells can produce over 10,000 virions.

H5N1 avian influenza

Current outbreak affecting birds and potentially mammals.

Bird flu impact

Killed nearly 60 million birds in 49 states.

Influenza susceptibility

Elderly and young are most affected during epidemics.

Genome reassortment

Influenza maximizes gene mixing to evade immunity.

Influenza mortality

Causes approximately 36,000 deaths annually in the US.

Egg price increase

Average price rose $2.60 due to bird flu.

Virus transmission potential

Concerns about bird flu jumping to humans.

Pandemic

Widespread disease affecting global human population.

Influenza Virus Strain

Variant of virus causing flu, potentially zoonotic.

Avian H5N1 Flu

Bird flu strain with high human mortality rate.

Mortality Rate

Percentage of deaths in infected population.

1918 Influenza Pandemic

Deadly flu outbreak killing 20% of global population.

CDC Statistics

Data on disease prevalence and impact from CDC.

H5N1 Transmission

Spread occurs through contact with infected poultry.

HIV

Retrovirus causing acquired immunodeficiency syndrome (AIDS).

Lentivirus

Slow-progressing retrovirus affecting immune system.

Global HIV Prevalence

Approximately 33 million people living with HIV.

AIDS Mortality

3 million deaths annually due to AIDS.

Initial AIDS Case

First reported case in the US was 1981.

HIV Infection Rate

1 in 100 adults infected, equal among genders.

High-Risk Behavior

Includes unprotected sex and needle sharing.

CD4+ T Lymphocytes

White blood cells crucial for immune response.

Clinical Latency

Phase of slow T cell loss in HIV infection.

Opportunistic Infections

Infections taking advantage of weakened immune system.

HIV Structure

Includes capsid, envelope, and spike proteins.

Reverse Transcriptase

Enzyme converting viral RNA into DNA.

HIV Treatment

Combination of antiviral drugs to manage infection.

HIV Genome

Contains gag, pol, and env genes for replication.

gag Gene

Encodes capsid and matrix proteins in HIV.

pol Gene

Encodes reverse transcriptase and integrase enzymes.

env Gene

Encodes envelope proteins for HIV virion.