• Spikes
• Found on both naked and enveloped viruses
• Project from either the nucleocapsid or envelope
• Allow viruses to dock with their host cells
• Virion
• Fully formed virus able to establish infection in a host
The Viral Capsid: The Protective Outer Shell
• Capsomeres
• Identical protein subunits that spontaneously self assemble to form the capsid
• Helical capsid
• Rod-shaped capsomeres that form a continuous helix around the nucleic acid
• Icosahedral capsid
• Three-dimensional, 20-sided figure with 12 evenly spaced corners
The Viral Capsid
• Complex capsids
– Found in bacteriophage, the viruses that infect bacteria
– Have multiple types of proteins
– Take shapes that are not symmetrical
The Viral Envelope
• Composed of the membrane system of the host
– Cell membrane or nuclear membrane
– Regular membrane proteins are replaced with viral proteins
– Spikes: protruding glycoproteins essential for attachment to the host cell
Nucleic Acids: At the Core of a Virus
• Genome: the full complement of DNA and RNA carried by a cell
• Viruses contain either DNA or RNA but not both
• The number of viral genes is small compared to that of a cell
• Possess only the genes necessary to invade host cells and redirect their activity
Nucleic Acids
• Positive-sense RNA
– Single-stranded RNA genomes ready for immediate translation into proteins
• Negative-sense RNA
– RNA genomes that need to be converted into the proper form to be made into
proteins
Other Substances in the Virus Particle
• Enzymes for specific operations within the host cell
– Polymerases: synthesize DNA and RNA
– Replicases: copy RNA
– Reverse transcriptase: synthesizes DNA from RNA
• Found on both naked and enveloped viruses
• Project from either the nucleocapsid or envelope
• Allow viruses to dock with their host cells
• Virion
• Fully formed virus able to establish infection in a host
The Viral Capsid: The Protective Outer Shell
• Capsomeres
• Identical protein subunits that spontaneously self assemble to form the capsid
• Helical capsid
• Rod-shaped capsomeres that form a continuous helix around the nucleic acid
• Icosahedral capsid
• Three-dimensional, 20-sided figure with 12 evenly spaced corners
The Viral Capsid
• Complex capsids
– Found in bacteriophage, the viruses that infect bacteria
– Have multiple types of proteins
– Take shapes that are not symmetrical
The Viral Envelope
• Composed of the membrane system of the host
– Cell membrane or nuclear membrane
– Regular membrane proteins are replaced with viral proteins
– Spikes: protruding glycoproteins essential for attachment to the host cell
Nucleic Acids: At the Core of a Virus
• Genome: the full complement of DNA and RNA carried by a cell
• Viruses contain either DNA or RNA but not both
• The number of viral genes is small compared to that of a cell
• Possess only the genes necessary to invade host cells and redirect their activity
Nucleic Acids
• Positive-sense RNA
– Single-stranded RNA genomes ready for immediate translation into proteins
• Negative-sense RNA
– RNA genomes that need to be converted into the proper form to be made into
proteins
Other Substances in the Virus Particle
• Enzymes for specific operations within the host cell
– Polymerases: synthesize DNA and RNA
– Replicases: copy RNA
– Reverse transcriptase: synthesizes DNA from RNA
