Acellular Microbes

Infectious Agents

Viruses Range from nm. academic.pgcc.edu/.../Chapter%2013/size.html

All Organisms Have the Potential to be Infected by Some Type of Virus. E. Coli being attacked by lambda bacteriophage. /m/foto/ LamAttack.html Tobacco Mosaic Virus. /tob amo1.htm Leaf left = uninfected tobacco leaf. Right leaf = infected leaf. /n68 39/full/411848a0.html Man infected with small pox. ism/spoxphoto1.htm Small pox virus. ih.gov/ICTVdb/I mages/Murphy/ Dow..

Sooooo………. what is a virus?

Virus 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 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 Virus

Virus 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 Classification

Where did viruses come from?

Virus Origin 3 Major Theories 1. 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.... 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!

Retrovirus 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 (

“Junk DNA” Many retroviruses are responsible for “junk DNA” in our genome. Illustration by James Collins ( )

Sheep, Viruses, and Dr. Spencer

Bacteriophage A virus that infects bacteria. 2 types 1. Virulent Bacteriophage 2. Temperate Bacteriophage

Virulent Bacteriophage Causes Lytic Cycle (5 steps) 1. Attachment 2. Penetration 3. Biosynthesis 4. Assembly 5. Release textbookofbacteriology.net oceanworld.tamu.edu

Temperate Bacteriophage Do not immediately begin lytic cycle. Their DNA remains embedded in bacterial cell chromosome.

Animal 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

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 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 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.

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

Viroids and Prions

Viroids 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 potatoes

Proteins Left = unfolded protein; Right = folded protein

Prions Left = correct protein folding; Right = wrong protein folding

Prions 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 Infections Sheep infected with scrapie. ( Deer infected with “chronic wasting disease.” ( Bovine spongiform encephalopathy, “mad cow disease.”

Prion Human Infections Kuru infected boy. Papua, New Guinea. pathology.mc.duke.edu Creutzfeldt-Jakob disease. Fatal familial insomnia

The End