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Viral Structure & Functions - Coggle Diagram
Viral Structure & Functions
Viral Morphology
Helical → Ebola, Rabies
Polyhedral (Icosahedral) → Adenovirus, Poliovirus
Enveloped Icosahedral → Herpesvirus
Shapes and forms of viruses
Complex → T-bacteriophage (dsDNA)
Yellow Fever
Transmission:
Sylvatic cycle: Mosquito–Monkey–Human
Urban cycle: Human–Mosquito–Human
Reservoir: Monkeys
Agent: Flavivirus (ssRNA, enveloped)
Prevention: Vaccine (attenuated 17D strain), mosquito control
First discovered human viral disease
No specific treatment
Host Range & Specificity
Viruses infect specific hosts or cells
Determined by attachment sites & host receptors
Broad range: rare
Narrow range: most viruses
Phage therapy: bacteriophages target specific bacteria
Animal Virus Replication
Attachment → Entry (fusion/pinocytosis) → Uncoating → Biosynthesis → Assembly → Release
DNA Viruses: replicate in nucleus (except poxvirus)
Steps in animal virus multiplication
RNA Viruses: replicate in cytoplasm
History of Virology
1886 — Adolf Mayer → Tobacco Mosaic Disease (TMD) transmissible
1892 — Dmitri Iwanoski → Filterable agent concept
Discovery of viruses as filterable agents
1930s — Wendell Stanley → Isolated TMV; electron microscope
First human viral disease → Yellow Fever (Walter Reed, 1901)
Bacteriophage Life Cycles
Lytic Cycle
T4 Phage (virulent)
Attachment → Penetration → Biosynthesis → Maturation → Release
Lysogenic Cycle
Lambda Phage (temperate)
Results of lysogeny:
Immunity to reinfection
Phage conversion (e.g., diphtheria toxin)
DNA integrates into host genome → prophage
Phage reproduction strategies
Viral Structure
Components and organization of viruses
Capsid
Protein coat
Made of capsomeres
Envelope
Derived from host membrane
Contains viral proteins
Nonenveloped = naked viruses
Spikes
Glycoprotein projections
Function: attachment to host cells
Example: Hemagglutinin (H), Neuraminidase (N)
Virion
Fully infectious particle (nucleic acid + coat)
Latent & Retroviruses
Latent infections: reactivated by stress
Herpes simplex (cold sores), Varicella-zoster (shingles)
Retroviruses: RNA → DNA via reverse transcriptase
Example: HIV integrates into host genome as provirus
Can remain latent or express genes later
Viruses that remain dormant or integrate into host DNA
Virus Overview
Definition
Nonliving entities
Require host cells for replication
Characteristics
Contain DNA or RNA (not both)
Protein coat (capsid)
May have an envelope
Viruses are obligatory intracellular parasites
Differences from bacteria
Sensitive to interferon
No plasma membrane, ribosomes, or ATP generation
Not sensitive to antibiotics
Influenza
Types:
A – pandemic potential
B – localized outbreaks
C – mild
Antigenic Drift: minor mutations (missense)
Spikes:
H (Hemagglutinin) – attachment
N (Neuraminidase) – release
Antigenic Shift: major recombination → pandemics
Genome: 8 RNA segments
Prevention: annual vaccine, antigen monitoring
Family: Orthomyxoviridae
Treatment: neuraminidase inhibitors
RNA virus with changing surface antigens
Viral Genetic Material
ssDNA → Parvoviridae (Parvovirus)
dsDNA → Herpesviridae (Simplexvirus), Poxviridae
Viral genomes vary by type of nucleic acid
+ssRNA → Picornaviridae (Enterovirus, Rhinovirus)
-ssRNA → Filoviridae (Ebola)
dsRNA → Reoviridae (Rotavirus)