Viruses, Viroids and Prion

Viral characteristics

*Viruses are extremely small *Viruses can cause cancer *Viruses can go underground *Viruses cause disease *Viruses are tools in research and medicine *Viruses can infect most any life form

Life cycle of virus

1. Adsorption 2. Entry 3. NA replication 4. Protein synthesis 5. Exit

Icosahedral

Adenovirus -20 sided -equilateral triangles -most common capsid type

Bacterial & Archaean viruses

Bacteriophages -usually DNA virus ex: T2, T4. lambon

Protein Spikes

Binds to receptor protein: lock and key Spikes are viral proteins (enzyme function, attachment) Examples: H5N1 influenza virus H= hemagglutinin N= neuraminidase HIV -gp120. The receptor determines which cell to infect.

Viral diseases

Blood: lukemia AIDS Respiratory: Influenza, cold Nervous: polio, meningitis, rabies Cancer: burkitt's lymphoma, cervial, liver Skin: measles, rubella, chickenpox, shingles, herpes, warts GI system: hepatitis (A,B,C,D,E) gastroenteritis, mumps

Penetration and Entry

Capsid Rearrangement -nucleic acid injection Envelope/membrane fusion Receptor mediated endocytosis

Protozoan & algal viruses

Chlorella virus ATCV-1 ( possible human infection?) Pithivirus- infects amoebas

Is there a virus tree of life?

Concept of virus "species" - phenotypic similarity, genetic similarity of specific genes, establish relationships between similar viruses, but not useful to connect the tree. *most virus families DO NOT share genes, 1 branch of all viruses like retro virus, can group into how similar their genes are for that specific protein.

Other virus shapes

Filamentous (filovirus) Bullet shapes (rhabdovirus) Cone shaped (HIV)

ss RNA Virus

HIV, influenza virus

ds DNA Virus

HSV, T-4 Bacteriophage

Animal virus families

Herpesviridae: herpes, chicken pox, mono Adenoviridae: respiratory infection Papovaviridae: genital warts, cervical cancer Hepadnaviridae: hepititis B, liver cancer Paramyxoviridae: cold, measles, mumps Filoviridae: evola, marburg Orthomyxoviridae: flu retrovirus: HIV, AIDS coronaviridae: SARS

Classification of viruses

Host Range Structure: nucleic acid, capsid, envelope, size.

Mycovirus

Infect fungi

Helical

Influenza virus Tobacco mosaic virus

Prions

Misfolded proteins Normal function -stem cells of bone marrow, neural stem cells? synaptic transmission? Nonliving, mad cow disease.

Receptor Mediated Endocytosis

Naked or enveloped viruses "Trojan Horse"

Virus Structure

Nucleic acid -DNA, RNA Protein coat Envelope

Virion release

Often involves cell death Naked viruses (host cell lysis) Enveloped viruses (host cell lysis, budding) Envelope- budding off virus assembles at very edge of cell and can push itself out, and punch off along with coated membrane., this allows virus to escape host cell, naked don't have any membrane- host cell just ruptures and spills all virus particles into the environment.

Genetic Material

Only one type of nucleic acid is ever found in a virus.

ds RNA Virus

Orbivirus

ss DNA Virus

Parvovirus

Envelope

Phospholipid membrane host derived ether inactivation herpes virus, influenza virus, HIV

Size range

Pithovirus: 1500 nm Mimivirus: 400 nm Parvovirus: 20 nm

Capsid

Protein coat: capsomeres/promoters Virus shape Protection of NA Host Recognition Entry

Special case: RETROVIRUS

RNA ->DNA reverse transcriptase (inserts complimentary DNA to match RNA) DNA -template for making RNA, integration into host DNA *unique to retrovirus

Adsorption

Receptor proteins (rabies: AchR, HIV: CD4) Binding is specific ( host organism, cell type) Helper T-Cells targeted, specific receptor necessary once connected, can trigger reception.

Other virus proteins

Reverse transcriptase RNA polymerase- proteins that are immediately needed for virus replication or assembly, not found in host cell.

Diversity of Virus Chromosomes

Single or segmented (16) Linear or circular (HPV) Haploid or Diploid (HIV) Can contain as few as 2 genes (circovirus) or as many as 2500 (Pandovirus) Genome size ranges from 1800 bp to 2,800,000 bp

Lytic cycle

Stands for lysis spilling out of virus, whole cell dies, infects nearby cells.

Complex

T-4 Bacteriophage Vaccinia (pox virus)

Plant viruses

Tobacco mosaic virus

Host Range

Which type of organisms can be your host. determines tissue that is infected.

Viroids

circular ssRNA plant disease, extremely smaller.

Life cycle of HIV

enveloped ss RNA virus *attachment: gp120 *entry of HIV: envelope/membrane fusion *replication:reverse transcriptase RNA->DNA *integrase: inserts HIV DNA -> host DNA *Transcription: HIV mRNA (in nucleus) *Translation: HIV polyprotein *assembly at plasma membrane *maturation: protease cuts polyprotein to right size

Envelope membrane fusion

enveloped viruses: HIV

Lysogenic cycle

infects the host cell, inserts DNA, DNA is integrated into host cell DNA, dormant state. *Bacteriophages *Herpes Virus/HIV *Dormancy *Latency *Lysogeny -prophage -provirus (once inside your chromosome)

Animal Virus

major human disease, when they infect cells, they usually damage them.

Viral Protein Synthesis

translation of mRNA self assembly use mRNA from virus to make virus proteins using our cell's ribosomes.

Viral NA Replication

virus shuts down whole cell, and all cells resources are used to make more of the virus. DNA viruses RNA viruses RNA -> RNA RNA -> DNA