Eukaryotes and Viruses Chapters 12 and 13

Viral Characteristics and Structure Why Viruses aren’t Alive

General Characteristics of Viruses Name derives from the Latin for “poison” Obligatory intracellular parasites Referred to as filterable Contain a single type of nucleic material The nucleic material is covered in a protein coat. Use the synthesis machinery of the host to multiply.

Why are they not Alive? No independent metabolism or reproduction No single phylogenetic origin No cellular structure No ribosomes Though they DO evolve and reproduce.

Host Range Viruses have a specific subset of cell types they will infect, referred to as Host Range. Most viruses can only infect a single species Some viruses can cross species barriers Numerous factors influence host range Viruses that infect bacteria are referred to as bacteriophage or simply phage.

Staphylococcus Bacteria Viral Particle Size Staphylococcus Bacteria 1 μm in diameter Poxviridae Lentiviruses Picornaviridae Bacteriophage

Viral Structure A Virion is a complete, infectious viral particle and is composed of… Nucleic Acid Capsid and Envelope

Nucleic Acid Only a single type of nucleic acid (RNA or DNA) is present in any species of virus. Unlike cellular life, viral nucleic acid can be either single or double-stranded (again only a single type per species) Size of the genetic structure can range from a few thousand base pairs to a quarter of a million

Capsid and Envelope Capsids are regular repeating protein structures composed of capsomeres. Some viral species also have a host-derived envelope surrounding the capsid Some viral species have protein/ carbohydrate “spikes” rising from the surface that can be used for identification

Viral Morphology

Viral Taxonomy How do you do a taxonomy of something that isn’t alive?

Viral Taxonomy Without a shared phylogeny there is no use for the higher taxons (Domain, Kingdom, Phylum, and Class) Typically viral species are referred to by Order, Family, Genus and a descriptive common name (in place of a species epithet) Based on Nucleic Acid type Strategy of replication Morphology Host range

Viral Replication No, not 1 becomes 2, more like 1 becomes 1000.

Growing Bacteriophage

Growing Animal Viruses

Viral Identification Polyphasic Identification Morphology Detection of Antibodies Western Blotting of known viral proteins Nucleic Methodologies PCR RFLP RNA PCR

Lytic Bacteriophage Cycle Attachment Release Penetration Biosynthesis Maturation

Lysogenic Bacteriophage Cycle Lytic Cycle

Animal Unenveloped DNA Viral Replication

DNA vs. RNA Viral Replication There are various types of RNA viruses. Replication of the Genetic Material can be simple or a multistep process. +RNA, direct translation and replication by viral protein -RNA, indirect translation and replication by viral protein dsRNA, direct translation and relication by viral protein Retroviruses, conversion of RNA to DNA, integration and then production by host.

Comparison Bacteriophage Animal Attachment to Cell Wall proteins. Viral DNA is injected into cell No removal of capsid required Biosynthesis in cytoplasm Lysogeny Host cell lysed for release Attachment to plasma membrane proteins and glycoproteins. Capsid enters cells Capsid removed by enzymes Biosynthesis in nucleus or cytoplasm Latency Enveloped viruses bud and nonenveloped rupture.

Viruses and Cancer One of many factors

Oncogenic Viruses Some viruses and known to help trigger cancers, called oncogenic viruses. These viruses affect oncogenes, natural parts of our genetic structure that can cause cancer. The process of becoming cancerous is termed transformation. Oncogenic Viruses integrate into the host genetic material.

Known Oncogenic Viruses Type of Virus Viral Species Associated Cancer DNA Human Papillomavirus Cervical Cancer Epstein-Barr Virus Burkitt’s Lymphoma Hepatitis B Virus Liver Cancer Kaposi Sarcoma-Associated Hepervirus Kaposi Sarcoma Merkel Cell Polyomavirus Merkel Cell Carcinoma RNA Human T-Lymphotropic Virus 1 Leukemia Hepatitis C Virus

Latency, Persistence and the Prions

Acute, Latent, and Persistent Viral Infections Acute Infections are those that cause immediate proliferation. Latent infections can occur by itself or after an acute infection, where the viral load remains undetected for a long period of time before reemerging quickly. Persistent Infections are ones where the viral load build over a long period of time.

Graph of Acute, Latent and Persistent Viral Infections

Prions Prions are infectious protein particles Prions are altered forms of a normal protein in the host that can catalyze the alteration of other “normal” protein particles to the “prion” state They cause neurological degradation and death with no known treatment. Since each prion protein is infectious, they are extremely resistant to control measures.

Prion Reaction PrPC + PrPSc  2 PrPSc