18.1 Studying Viruses and Prokaryotes Characteristics of Living Organisms Made up of cell(s) Reproduce on their own Have genetic information, DNA Grow and Develop Obtain and use materials and energy (metabolism) Maintain and internal balance (homeostasis) Respond to their environment Evolve, change over time

18.1 Studying Viruses and Prokaryotes Viruses, bacteria, viroids, and prions can all cause infection. Any disease-causing agent is called a pathogen. viruses nm prokaryotics cells ,000 nm prion 2-10 nm viroids nm eukaryotics cells 10, ,000 nm 100 nm 1 nanometer (nm) = one billionth of a meter

18.1 Studying Viruses and Prokaryotes What is the difference between bacteria and viruses? A virus is made of DNA or RNA and a protein coat. –non-living pathogen –can infect many organisms Bacteria are one- celled microorganisms that can cause infection. –living pathogen

18.1 Studying Viruses and Prokaryotes Viruses differ in shape and in ways of entering host cells. Viruses have a simple structure. –genetic material (DNA or RNA) –Capsid (a protein shell) –maybe a lipid envelope, a protective outer coat capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

18.1 Studying Viruses and Prokaryotes Viruses enter cells in various ways. colored SEM; magnifications: large photo 25,000; inset 38,000x –bacteriophages pierce host cells

18.1 Studying Viruses and Prokaryotes –viruses of eukaryotes enter by endocytosis Viruses enter cells in various ways.

18.1 Studying Viruses and Prokaryotes They are simply packaged sets of genes that move from one host cell to another. The different viral shapes, play a role in how viruses work. It is how they identify their host cell. capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

18.1 Studying Viruses and Prokaryotes Enveloped Virus Ex: influenza

18.1 Studying Viruses and Prokaryotes Helical virus Example: Rabies

18.1 Studying Viruses and Prokaryotes

Polyhedral Virus Example: Foot and mouth (coxsackie virus)

18.1 Studying Viruses and Prokaryotes

Viruses are specific in what they infect Most viruses are species specific –Ex. Small pox-humans only, tobacco mosaic virus- plants only, bacteriophages-bacteria only can only affect a limited range of hosts –host range is determined by the specificity of attachment to the cells, which depends on properties of both the virion's coat and specific receptors on the cell surface Some can affect a number of species with in mammals ex. Rabies

18.1 Studying Viruses and Prokaryotes The genetic material in viruses differ from prokaryotes and eukaryotes. They can have either DNA or RNA, but never both. capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

18.1 Studying Viruses and Prokaryotes A prion is made only of proteins. –causes misfolding of other proteins –results in diseases of the brain -Alzheimer's disease -Creutzfeldt-Jakob disease (mad cow disease) -Down's syndrome -Fatal familial insomnia -Kuru Leprosy

18.1 Studying Viruses and Prokaryotes A viroid is made only of single-stranded RNA. –causes disease in plants –passed through seeds or pollen Tobacco mosaic virus

18.1 Studying Viruses and Prokaryotes Viruses can only reproduce after they have infected host cells. HIV leaving host cell

18.1 Studying Viruses and Prokaryotes Bacteriophages infect bacteria. The T-4 Bacteriophage virus is about to attack the bacterium. The virus injects its genetic material into the bacterium. The bacterium explodes after it is forced to make copies of the virus!

18.1 Studying Viruses and Prokaryotes Several viruses have been linked to certain types of cancer: The Epstein-Barr virus has been linked with Burkitt's lymphoma. The Hepatitis B and C viruses have been linked with liver cancer in people with chronic infections. HTLV-I, a retrovirus, has been linked to T-cell leukemia. Papilloma viruses have been linked with cervical cancer.

18.1 Studying Viruses and Prokaryotes Lytic infection 1. Bacteriophage injects DNA into cell 2. Viral DNA forms plasmid in host 3. May enter lysogenic cycle 4. Host makes new virus Final: Host explodes (lyses), spreading virus

18.1 Studying Viruses and Prokaryotes host bacterium The bacterophage attaches and injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are able to infect new host cells. The viral DNA directs the host cell to produce new viral parts. The parts assemble into new bacteriophages. The viral DNA forms a circle (plasmid). Lytic infection causes the cell to burst. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

18.1 Studying Viruses and Prokaryotes Lysogenic Cycle 1. Bacteriophage injects DNA into cell 2. Viral DNA forms prophage (part of host DNA) 3. Viral DNA replicates with host 4. Cell reproduces producing many copies of virus Final: Cell has dormant virus or may enter lytic cycle

18.1 Studying Viruses and Prokaryotes A lysogenic infection does no immediate harm. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. The prophage may leave the host’s DNA and enter the lytic cycle.

18.1 Studying Viruses and Prokaryotes –HIV –Retrovirus destroys white blood cells –Causes AIDS HIV-infected white blood cell Viruses cause many infectious diseases

18.1 Studying Viruses and Prokaryotes Vaccines are made from weakened pathogens. A vaccine stimulates body’s immune system to prepare for attack from microbes

18.1 Studying Viruses and Prokaryotes Vaccines Characteristics: Made of weakened virus or parts of virus Body’s immune system allowed to recognize and build antibodies