VIRAL STRUCTURE Image source: healthoma.com

Sources: raritanval.edu; slavirusportfolio.wikispaces.com, virology.wisc.edu

Vocabulary Overview Nucleic Acid: The genetic material that determines the structure and function of a specific virus The RNA or DNA may be either… double-stranded (like the DNA in your own cells) -or- single-stranded (much like the mRNA made during transcription) Image source: DNA-chem.ucsb.edu RNA-human.freescience.org

Vocabulary Overview Sense Strand (+): A single stranded RNA that can serve as it’s own mRNA for replication Antisense Strand (-): A single stranded RNA that CAN NOT serve as its own mRNA for replication. The antisense strand MUST synthesize a complementary mRNA strand before replication can occur.

Vocabulary Overview Lipid Bilayer: The lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cells. Generally, the envelope is made from a lipid bilayer and contains glycoprotein spikes. Glycoprotein Spikes: Protein spikes that are important in determining the host range and antigenic properties. These are the structures that a host cell will “recognize” and allow viral attachment.

Vocabulary Overview Capsid: The protein coat or shell of a virus particle, surrounding the nucleic acid or nucleoprotein core. The capsid of Kaposi’s Sarcoma Associated Herpes Virus Image source: mdicine.virigina.edu

Vocabulary Overview Envelope: An additional covering that consists of a lipid bilayer that closely surrounds the capsid. The exterior of the envelope is studded with glycosylated proteins that aid the virus in attacking specific receptor cells. Virus entering/exiting host cell The envelope of a virus is obtained when a virus “buds” out of a host cell, taking the proteins of the cell with it. Detailed Description of Herpes Virus Exiting Cell Source: youtube.com ( (

Image Sources:molbio.princeton.edu biotechlean.org.nz concerncrisis.blogspot.com

So…How are viruses different from other cells?? VirusesProkaryoteEukaryote Size: nanometers micrometers1-100 micrometers Genetic Material (nucleic acid): DNA or RNA (can be double or single stranded) DNA (circular or linear) DNA Outer Covering:Capsid or envelope Cell membrane and cell wall Cell wall or Cell Membrane Replication Method: Lytic or Lysogenic Cycle Binary fissionMitosis/Meiosis Living or Non- Living: Non-livingLiving

The Genetic Code: What is in a Virus?? Unlike prokaryotes or eukaryotes, viruses may contain either DNA or RNA as their genetic basis. They are not limited to the use of ONLY DNA In addition to using either RNA or DNA, viruses may use single (ss) or double (ds) stranded nucleic acids The type of genetic material within a viral capsid dictates the type of virus

Types of Viruses based on Nucleic Acid Type of Nucleic AcidExample Double Stranded (ds) DNAAdenovirus, Herpesvirus, Poxvirus Single Stranded (ss)(+) sense DNAParvovirus Double Stranded (ds) RNARotavirus Single Stranded (ss)(+) sense RNAPicornavirus, Togavirus Single Stranded (ss)(-) sense RNAOrthomyxovirus, Rhabdovirus Single Stranded (ss)(+) RNA with DNA Intermediate Retrovirus (this genome is (+) sense, BUT it does not serve as mRNA as expected. The ssRNA serves as a reverse transcription template. A common example is HIV) Source:

Types of Viral Structures Icosahedral Helical Tailed Phages

Icosahedral Viruses Example: Human Adenovirus These viruses have a polyhedron shape that allows for 20 equilateral triangular faces and 12 vertices between the faces. These viruses may either be covered in a single capsid (naked) or include an outer envelope (enveloped) Image source: serc.carleton.edu

Helical Viruses Example: Tobacco Mosaic Virus Helical viruses have a rod-like symmetry Identical proteins assemble themselves into a helical array surrounding the nucleic acid. The enclosed nucleic acid follows a similar spiral path Image source: britannica.com

Tailed Phage Viruses example: T-4 Bacteriophage Tailed phage viruses normally attack bacterial cells. These viruses have a complex structure that consists of a capsid head (where DNA or RNA is stored), a helical tube (comprised of a rod and sheath), and tail fibers (which aid in attachment to host cells) Image source: microscopesblog.com

FIVE BASIC STRUCTURAL FORMS OF VIRUSES IN NATURE Naked icosahedral e.g. poliovirus, adenovirus, rhinovirus hepatitis A virus, human papilloma virus Naked helical e.g. tobacco mosaic virus. So far no human viruses with this structure are known Enveloped icosahedral e.g. herpes virus, yellow fever virus, rubella virus, chicken pox (varicella zoster virus) Enveloped helical e.g. rabies virus, influenza virus, parainfluenza virus, mumps virus, measles virus Complex e.g. poxvirus, T-4 bacteriophage Source:

DNA or RNA Icosahedral (enveloped) Capsomere protein Helical (naked) Helical (enveloped) Icosahedral (naked)