Wednesday in PAP Biology

• REMINDERS:– You have a vocabulary check today (list 3)– You have a Taxonomy assessment Monday– You have a Virus assessment next Friday, as well as a 4a

review assessment AND vocab check!!! BE READY!

• Today we are:– Finishing/reviewing classification– Taking notes and discussing Viruses – Creating a virus poster

Virus Poster (using book and notes to complete)

Include all of the following on your poster:1. Structure of a typical animal virus AND bacteriophage,

with labeled structures (capsid, envelope, genetic material, etc)

2. Function of viruses 3. Drawing and description of how viruses reproduce

(both cycles)4. Viruses caused by both Lytic and Lysogenic infections5. Section comparing viruses to prokaryotes

VirusesBiology 4(C)

Learning objectives– Know the structure of viruses– Compare viruses to cells– Understand viral reproduction– Understand the role of viruses in

diseases

Viruses

Do viruses fulfill the characteristics of life? NO– Viruses cannot reproduce on their own

• Need host machinery (ribosomes)

– Viruses cannot metabolize energy• Need host energy

– No, not considered biotic (a living thing)

What is a Virus?

Capsid – protein shell that protects genetic information of virus

Viral Structure - Bacteriophage

Genetic information – strands of DNA or RNA used to make viral proteins inside infected hosts

Viral Structure - Bacteriophage

Tail – protein shaft that contracts to inject viral genetic information into host

Viral Structure - Bacteriophage

Tail fibers – proteins that attach to the outside of a host

Viral Structure - Bacteriophage

Membranous envelope – lipids that attach and fuse to hosts

Viral Structure – Other Types

Viruses• DNA or RNA• Need a host to

replicate• Never contain

organelles• Do not convert

energy

Cellular Life• Only DNA• Can reproduce

independently• Eukaryotes

contain organelles• Convert energy to

perform tasks

Viruses vs. Cellular Life

• Viruses need a host to reproduce– Goal: create more copies of their genetic material

• Two methods– Lytic Cycle– Lysogenic Cycle

Viral Reproduction

• Lytic Cycle– Attaches to host– Injects genetic material into host– Cellular machinery duplicates genetic material and creates

viral proteins (capsids, tail fibers)– New viruses are assembled– New viruses exit the cell by bursting the cellular membrane

• End result – more viruses made, cell dies

Viral Reproduction – Lytic Cycle

Lytic Cycle Attachment

Entry

ReplicationAssembly

Release

Viral Reproduction – Lytic Cycle

• Lysogenic Cycle– Attaches to host– Injects genetic material into host– Viral genetic material is inserted into host genome– Viral genetic material lies dormant– When cell reproduces, new copies have viral genetic

information– Environmental stimulus sends viral DNA into lytic cycle

• End result – more viral genome made, cell lives

Viral Reproduction – Lysogenic Cycle

Lysogenic CycleAttachment

Entry

ReproductionInsertion

Separation

Viral Reproduction – Lysogenic Cycle

Lytic Cycle• New viruses

made• Cellular host dies

Lysogenic Cycle• Genome copies

made• Cellular host lives

Viruses can use both cycles1. Infect many cells with lysogenic2. Create many viruses at once with lytic

Viral Reproduction

Lysogenic Cycle:– Herpes– HPV– Chicken Pox (can

become shingles)– HIV– Hepatitis B

Lytic:– SARS– Common Cold– Influenza– Rabies– AIDS phase of HIV– Tobacco Mosaic

Virus (in plants)

Common Viral Infections

Lytic & Lysogenic Cycles

Viral Reproduction

• AIDS – acquired immune deficiency syndrome– Describes loss of immune system because of HIV

• Caused by HIV - human immunodeficiency virus– makes helper T cells useless

• Prevention– No vaccine– Limit transmission (use condoms)– Avoid transmission (use clean needles)

Viral Diseases - AIDS

• Influenza (the flu)– Causes fever, fatigue, and respiratory infections– More severe than common cold, can be deadly

Viral Diseases - Influenza

• Caused by a variety of influenza viruses– Change often, new vaccines yearly– Can blend with bird and swine

strains to produce new viruses

• Prevention– Seasonal vaccine– Limit transmission (wash hands)

Image by NIAD [Public Domain]

• The Common Cold– Causes fever, fatigue, and respiratory infections– Less severe than influenza

• Caused by a variety rhinoviruses– Over 200 different virus strains

• Prevention– No vaccine– Limit transmission

(wash hands)

Viral Diseases – Common Cold

Image by Robin S [GNU]

• Hepatitis A– Causes inflammation of liver, jaundice appearance– Rarely results in liver failure

• Caused by a hepatitis A virus– Carried through infected food or water

• Prevention– Vaccine– Limit transmission

(wash hands, food)

Viral Diseases – Hepatitis A

Image by The CDC [Public Domain]

• Some animal viruses exit without lysing the host– Envelopes that fuse to the host cell’s plasma membrane

Viral Reproduction in Animals

Images by Matt Gonda [Public domain]

Viral Diseases – AIDS – HIV Replication

Graoh by Jurema Oliveira [GFDL]

Viral Diseases - AIDS

• Initial infection– Helper T cells rapidly decline– Viral genome rapidly increases

• Clinical latency– Viral genomes lay mostly dormant in infected cells

• AIDS– Rate of viral creation outweighs helper T cell creation

• Death– Immune system too weak to fight common pathogens

Viral Diseases - AIDS