Virus es Big Idea 3: Living systems store, retrieve, transmit, and respond to info essential to life processes.

Essential Knowledge 3C3: Viral replication results in genetic variation, and viral infection can introduce genetic variation into the hosts.

Structure of Viruses Viruses are not cells  small infectious particles consisting of nucleic acid in a protein coat or a membranous envelope

Viral Genomes Made of either: –Double- or single-stranded DNA, or –Double- or single-stranded RNA

RNA Viruses Need Reverse Transcriptase: enzyme that makes double stranded DNA to match w/ host cell Lack replication error-checking mechanisms  higher rates of mutation (HIV!)

Herpes Virus- DNA

Ebola Virus- RNA

Capsids and Envelopes A protein shell that encloses viral genome Built from protein subunits called capsomeres

Fig RNA Capsomere of capsid DNA Glycoprotein 18  250 nm 70–90 nm (diameter) Glycoproteins 80–200 nm (diameter) 80  225 nm Membranous envelope RNA Capsid Head DNA Tail sheath Tail fiber 50 nm 20 nm (a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4

Highly efficient  allow for rapid evolution and acquisition of new phenotypes ! Viral Replication

AKA: phages, viruses that infect bacteria Have a long capsid head that encloses DNA A protein tail attaches phage to host and injects DNA inside Bacteriophage

Fig µm

Viruses Need Hosts! Intracellular parasites that have a host range (a limited number of host cells that it can infect)

Viral Reproductive Cycles Virus VC

Transcription and manufacture of capsid proteins Self-assembly of new virus particles and their exit from the cell Entry and uncoating Fig VIRUS DNA Capsid 4 Replication HOST CELL Viral DNA mRNA Capsid proteins Viral DNA

Reproductive Cycles of Phages 1 st Rep Cycle: lytic cycle  Death of host cell Virulent phage: virus that only reproduces via lytic cycle

Fig Attachment 1

Fig Entry of phage DNA and degradation of host DNA Attachment 1 2

Fig Synthesis of viral genomes and proteins Entry of phage DNA and degradation of host DNA Attachment 1 2 3

Fig Phage assembly Assembly Synthesis of viral genomes and proteins Entry of phage DNA and degradation of host DNA Attachment HeadTailTail fibers 3

Fig Phage assembly HeadTailTail fibers Assembly Release Synthesis of viral genomes and proteins Entry of phage DNA and degradation of host DNA Attachment

2 nd reprod. Cycle: latent/lysogenic cycle No destroying host cell  viral DNA is mixed into host cell’s chromosome  prophage Gives host cell properties like increased pathogenicity in bacteria Reproductive Cycles of Phages

Phages that use both lytic and lysogenic cycles Env. signal can trigger switch Temperate Phages Lambda Phage  Attacks E. Coli

Fig Phage DNA Phage The phage injects its DNA. Bacterial chromosome Phage DNA circularizes. Daughter cell with prophage Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Cell divisions produce population of bacteria infected with the prophage. The cell lyses, releasing phages. Lytic cycle is induced or Lysogenic cycle is entered Lysogenic cycle Prophage The bacterium reproduces, copying the prophage and transmitting it to daughter cells. Phage DNA integrates into the bacterial chromosome, becoming a prophage. New phage DNA and proteins are synthesized and assembled into phages.

Evolution of Viruses Maybe plasmids?? (circular DNA in bacteria and yeasts) and transposons, small mobile DNA segments

Mimivirus (double-stranded DNA) is 2 nd largest virus discovered Virus evolved before or after cells?

Megavirus (2 strand DNA) Oct. 2011, largest virus

Harmless derivatives of pathogenic microbes that stimulate immune system to mount defenses against actual pathogen Viral infections cannot be treated by antibiotics Vaccines

With your partner, make a list of vaccines you have received!

Epidemic: New cases of a disease appear in a local area  aka outbreak If epidemic spreads to another locale  pandemic Epidemics vs Pandemics

Plant Viruses Most have an RNA genome –Horizontal transmission, entering through damaged cell walls –Vertical transmission, inheriting the virus from a parent

Viroids and Prions: Simple Viroids: circular RNA molecules that infect plants and disrupt growth Prions: slow-acting, virtually indestructible infectious proteins that cause brain diseases in mammals

Ex: Prion Mad Cow Disease

Ex: Prion Creutzfeldt Jakob Syndrome

Understanding Viruses Movie o/360cafa902fb60e55f61/Under standing-Viruses o/360cafa902fb60e55f61/Under standing-Viruses