Acellular MicrobesAcellular Microbes

Infectious AgentsInfectious Agents

VirusesViruses

Range from 10-300 nm.

academic.pgcc.edu/.../Chapter%2013/size.html

All Organisms Have the Potential to be All Organisms Have the Potential to be Infected by Some Type of Virus.Infected by Some Type of Virus.

E. Coli being attacked by lambda bacteriophage.

www.asm.org/division/m/foto/LamAttack.html

Tobacco Mosaic Virus.

www.ncbi.nlm.nih.gov/.../Milne/tobamo1.htm

Leaf left = uninfected tobacco leaf. Right leaf = infected leaf.

www.nature.com/.../v411/n6839/full/411848a0.html

Man infected with small pox.

www.idph.state.il.us/Bioterrorism/spoxphoto1.htm

Small pox virus.

www.ncbi.nlm.nih.gov/ICTVdb/Images/Murphy/Dow..

Sooooo……….Sooooo……….what is a virus?what is a virus?

Virus CharacteristicsVirus Characteristics

1. Have genetic material, either DNA or RNA. 2. Can’t replicate without a host cell. 3. Can’t divide by binary fission, mitosis, or

meiosis. 4. Can’t make their own energy (steal it from host

cell). 5. Can’t make their own protein or genetic

material (steal from host cell).

Characteristics of a Typical VirusCharacteristics of a Typical Virus

1. Consists of a genome of either RNA or DNA.

2. Genetic material surrounded by a capsid or protein coat.

Composed of small protein units called capsomeres.

3. Some viruses have an outer envelope.4. May also have a tail, sheath, and tail

fibers.

A Typical VirusA Typical Virus

Virus ClassificationVirus Classification

1. Type of genetic material. 2. Shape of the capsid. 3. Number of capsomeres. 4. Size of the capsid. 5. Presence or absence of an envelope. 6. Type of host it infects. 7. Type of disease it produces. 8. Target cell. 9. Immunologic or antigenic properties.

Viral ClassificationViral Classification

www.biotech100.com www.antibac2k.com

Where did Where did viruses come from?viruses come from?

Virus OriginVirus Origin

3 Major Theories1. Viruses are remnants of past infections

(e.g. mitochondrion/chloroplasts).2. Cells came before viruses.

• Viruses are degenerate cells or cell fragments.

3. Viruses represent a separate evolutionary branch

What if. . . .What if. . . .

Scientists found a cell that was as large or larger than some bacteria and that cell had the capabilities to produce almost everything it needed to “live.”

It required a host cell only to make some ribosomes.

Is it a virus or a living cell?

Meet Mimi!Meet Mimi!

http://www.microbiologybytes.com/virology/Mimivirus.html

RetrovirusRetrovirus Genetic information is

single-stranded RNA. Have a special enzyme

called reverse transcriptase.

This enzyme makes DNA from RNA.

Integrate their newly formed double-stranded DNA into the host cell.

Example = HIV

Human Immunodeficiency Virus (www.msu.edu)

““Junk DNA”Junk DNA”Many retroviruses are responsible for “junk DNA” in our genome.

Illustration by James Collins (www.rps.psu.edu )

Sheep, Viruses, and Dr. SpencerSheep, Viruses, and Dr. Spencer

BacteriophageBacteriophage

A virus that infects bacteria.2 types

1. Virulent Bacteriophage 2. Temperate Bacteriophage

Virulent BacteriophageVirulent Bacteriophage

Causes Lytic Cycle (5 steps)

1. Attachment 2. Penetration 3. Biosynthesis 4. Assembly 5. Release

textbookofbacteriology.net oceanworld.tamu.edu

Temperate BacteriophageTemperate Bacteriophage

Do not immediately begin lytic cycle.Their DNA remains embedded in bacterial

cell chromosome.

Animal VirusesAnimal Viruses Species specific. Attach to specific binding

sites on cells. This affects what species

and which cell type is infected.

Multiplication of Animal Viruses (6 steps)– 1. Attachment– 2. Penetration– 3. Uncoating– 4. Biosynthesis– 5. Assembly– 6. Release

www.heritageparkzoo.org

Budding Budding

A transmission electron microscopy (TEM) image of

influenza viruses budding from the surface of an infected cell.

(CNRI/Science Photo Library, National Audubon Society Collection/Photo Researchers, Inc.)

Antiviral AgentsAntiviral Agents Interfere with the

phases of viral multiplication.

May disrupt a binding site.

May disrupt an enzyme or protein.

May interfere with the synthesis of viral parts like DNA, RNA, or protein synthesis.

Oncogenic VirusesOncogenic Viruses

Viruses that cause cancer.

Ex. Human papillomaviruses (HPV – wart viruses) cause different types of cancers.– i.e. cervical cancer

and other types of cancers of the genital tract. Kaposi Sarcoma – caused by human

herpesvirus 8.

www.hyle.org

Plant VirusesPlant Viruses

Maize chlorotic mottle virus (MCMV) nu-distance.unl.edu

Viroids and PrionsViroids and Prions

ViroidsViroids

Consist of short, fragments of single-stranded RNA.

Only found in plants (so far).

Can interfere with plant’s metabolism, resulting in the plant being stunted or killed.

Ex. Potato spindle tuber

Left: normal potatoes; Right – infected potatoeswww.unece.org

ProteinsProteins

Left = unfolded protein; Right = folded protein

PrionsPrions

Left = correct protein folding; Right = wrong protein foldingwww.cogs.susx.ac.uk

PrionsPrions

Small infectious proteins.Cause fatal neurologic diseases in animals.Cause fatal spongiform encephalopathies.

– Brain becomes riddled with holes.

Brain with spongiform encephalopathy

webs.wichita.edu

Prion Animal InfectionsPrion Animal Infections

Sheep infected with scrapie. (www.gov.mb.ca)

Deer infected with “chronic wasting disease.” (http://www.fw.delaware.gov)

Bovine spongiform encephalopathy, “mad cow disease.”

Prion Human InfectionsPrion Human Infections

Kuru infected boy. Papua, New Guinea. pathology.mc.duke.edu

Creutzfeldt-Jakob disease. www.nlm.nih.gov

Fatal familial insomnia

The EndThe End