18.1 Studying Viruses and Prokaryotes KEY CONCEPT Infections can be caused in several ways.

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 A virus is made of DNA or RNA and a protein coat. –non-living pathogen –can infect many organisms A viroid is made only of single-stranded RNA. –causes disease in plants –passed through seeds or pollen

18.1 Studying Viruses and Prokaryotes A prion is made only of proteins. –causes misfolding of other proteins –results in diseases of the brain –Mad cow, scrapie, CJD, chronic wasting

18.1 Studying Viruses and Prokaryotes KEY CONCEPT Viruses exist in a variety of shapes and sizes.

18.1 Studying Viruses and Prokaryotes Viruses differ in shape and in ways of entering host cells. Viruses have a simple structure. –genetic material –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 Bacteriophages infect bacteria. capsid DNA tail sheath tail fiber

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 also fuse with membrane Viruses enter cells in various ways.

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. Viruses cause two types of infections. A lytic infection causes the host cell to burst with new viruses. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

18.1 Studying Viruses and Prokaryotes A lysogenic infection does no immediate harm. Can be activated later. Herpes simplex activates periodically 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 KEY CONCEPT Some viral diseases can be prevented with vaccines.

18.1 Studying Viruses and Prokaryotes Prevention of Viral infection Vaccines are made from weakened pathogens. A vaccine stimulates the body’s own immune response. Vaccines prepare the immune system for a future attack.

18.1 Studying Viruses and Prokaryotes Prevention of Viral disease Vaccines are one way to prevent the spread of viral disease. What else is effective? Hand washing Condoms Avoiding direct contact Preventing fluid transfer (sneeze, blood, saliva) Bleach, lysol, strong cleaners

18.1 Studying Viruses and Prokaryotes History of Vaccination Smallpox spread throughout Europe in the 1700’s influenza (flu) type symptoms, rash covering much of body, turning into puss filled sores that most often left blisters and deep scars complications from the disease led to blindness, kidney damage, and death in 40% of its victims

18.1 Studying Viruses and Prokaryotes in 1796, Edward Jenner, an English Physician, observed that there were many young women that were not affected by the virus, while some or all of the rest of the family was stricken

18.1 Studying Viruses and Prokaryotes Milkmaids often caught a mild form of cowpox, a similar disease that caused sores on the udders of cows, these women were often immune to smallpox Jenner found that by rubbing the pus from cowpox sores into scratches in the skin prevented people from getting smallpox Outbreaks of smallpox occurred in the1970's, and the World Health Organization declared eradication of the disease in 1980 (viral samples are kept in Moscow and in Atlanta)

18.1 Studying Viruses and Prokaryotes Treatment of Viral Diseases There are a very few number of viral diseases that can be actually Treated once infection has taken hold… Antivirals like Acyclovere & AZT stop viral replication

18.1 Studying Viruses and Prokaryotes KEY CONCEPT Bacteria and archaea are both single-celled prokaryotes.

18.1 Studying Viruses and Prokaryotes Prokaryotes are widespread on Earth. Prokaryotes can be grouped by their need for oxygen. –obligate anaerobes are poisoned by oxygen –obligate aerobes need oxygen –facultative aerobes can live with or without oxygen

18.1 Studying Viruses and Prokaryotes Bacteria and archaea are structurally similar but have different molecular characteristics. Bacteria commonly come in three forms. –rod-shaped, called bacilli Lactobacilli: rod-shaped Enterococci: spherical Spirochaeta: spiral Archaea have many shapes. – spiral, called spirilla or spirochetes – spherical, called cocci

18.1 Studying Viruses and Prokaryotes The bacterial colonies also are part of their naming… Staph are clumps Strep are chains

18.1 Studying Viruses and Prokaryotes Bacteria and archaea have similar structures. flagellum pili plasmid cell wall chromosome plasma membrance This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences. –plasmid –flagellum –pili

18.1 Studying Viruses and Prokaryotes Bacteria and archaea have molecular differences. GRAM NEGATIVEGRAM POSITIVE –Archaea have different lipids entirely –The amount of peptidoglycan within the cell wall can differ between bacteria

18.1 Studying Viruses and Prokaryotes Gram staining identifies bacteria. Gram-negative bacteria have a thin layer of peptidoglycan and stain red. Gram-positive bacteria have a thicker peptidoglycan layer and stain purple. –stains polymer peptidoglycan –gram-positive stains purple, more peptidoglycan –gram-negative stains pink, less peptidoglycan

18.1 Studying Viruses and Prokaryotes Bacteria have various strategies for survival. Prokaryotes exchange genes during conjugation. conjugation bridge TEM; magnification 6000x Bacteria may survive by forming endospores.

18.1 Studying Viruses and Prokaryotes KEY CONCEPT Prokaryotes perform important functions for organisms and ecosystems.

18.1 Studying Viruses and Prokaryotes Bacteria - what comes to mind? Diseases, Infections, Epidemics, Food Spoilage But, **Only 1% of all known bacteria cause human diseases **About 4% of all known bacteria cause plant diseases ***95% of known bacteria are non-pathogens

18.1 Studying Viruses and Prokaryotes Benefits of Microorganisms 1.Bacteria are primary decomposers - recycle nutrients back into the environment (sewage treatment plants) 2. Microbes produce various food products –cheese, pickles, sauerkraut, green olives –yogurt, soy sauce, vinegar, bread –Beer, Wine, Alcohol

18.1 Studying Viruses and Prokaryotes Prokaryotes provide nutrients to humans and other animals. Prokaryotes live in digestive systems of animals. –make vitamins (vitamin K and B vitamins) –break down food

18.1 Studying Viruses and Prokaryotes Prokaryotes play important roles in ecosystems. Prokaryotes have many functions in ecosystems. –photosynthesize –recycle carbon, nitrogen, hydrogen, sulfur –fix nitrogen

18.1 Studying Viruses and Prokaryotes KEY CONCEPT Understanding bacteria is necessary to prevent and treat disease.

18.1 Studying Viruses and Prokaryotes Some bacteria cause disease. Bacteria cause disease by invading tissues or making toxins. A toxin is a poison released by an organism.

18.1 Studying Viruses and Prokaryotes Normally harmless bacteria can become destructive. –may colonize new tissues

18.1 Studying Viruses and Prokaryotes –immune system may be lowered Normally harmless bacteria can become destructive.

18.1 Studying Viruses and Prokaryotes Antibiotics are used to fight bacterial disease. Antibiotics may stop bacterial cell wall formation. Antibiotics do not work on viruses. Prevention is best method to fight bacterial disease.

18.1 Studying Viruses and Prokaryotes Antibiotics can be used to help fight off bacteria

18.1 Studying Viruses and Prokaryotes Bacteria can evolve resistance to antibiotics. A bacterium carries genes for antibiotic resistance on a plasmid. A copy of the plasmid is transferred through conjugation. Resistance is quickly spread through many bacteria. Bacteria are gaining resistance to antibiotics. –overuse –underuse –misuse Antibiotics must be used properly.