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Virus and Bacteria Notes • Bacteria are grouped into two kingdoms: -Eubacteria and Arcahebacteria • -Eubacteria and Archaebacteria have different membrane lipids and archaebacteria lack the peptidoglycan found in eubacteria cell walls. • -Archaebacterial genes are more like those of eukaryotes than those of eubacteria. Bacteria are Prokaryotes and have: • • • • • • -Cell Wall -Cell Membrane -NO nucleus -Ribosomes -NO organelles -Flagella (for mobile species) • • • • Bacteria come in three shapes: Bacillus- rod shaped bacteria. Cocci- spherical shaped bacteria. Spirilla- spiral/corkscrew shaped bacteria Metabolic Diversity • Some bacteria are heterotrophs. They are referred to as chemoheterotrophs. • As bacteria take in organic molecules for both energy and a supply of carbon. • Some bacteria are autotrophs. They are photoautotrophs if they use light energy to convert CO2 and water to carbon compounds. These are often found near surfaces of lakes, streams, and oceans. • Chemoautotrophs can perform chemosynthesis that perform the same task as photoautotrophs except they do not need to use light. They rely on chemical reactions instead. Many are found at hydrothermal vents. Releasing Energy • Obligate aerobes- require a constant supply of oxygen • Obligate anaerobes- must live in the absence of oxygen • Facultative anaerobes- Can function with or without oxygen. Growth • _Binary_ Fission is when a bacteria divides in half producing identical cells. This is asexual and much simpler than mitosis. • _Conjugation__- Some bacteria can exchange genetic information this way when a hollow bridge forms between two bacteria cells and genes move from once cell to the other. SPORE Formation- In unfavorable conditions, bacteria can form spores that can remain dormant for months while conditions improve. Then the bacteria can germinate and grow again. Bacteria in the World Decomposers - Bacteria can help the ecosystem by breaking down dead tissue. Very important also in sewage treatments! Nitrogen Fixers- Bacteria can live in the nodules of plant roots and fix nitrogen (nitrogen fixation) which is critical in the nitrogen cycle. -Bacteria are also found in our intestines! They make vitamins that the body cannot produce by itself and we supply the bacteria with a warm and safe home. This is a mutual symbiotic relationship! • Bacteria can also cause disease in animals and plants. • -Bacteria can do this by damaging cells ant tissues directly. • -Or bacteria can release toxins that travel throughout the body and interfere with the normal activity of the host. http://www.nwlincs.org/mtlincs/pilot project/science/lsvirusbacteria.htm VIRUSES I. Virus Characteristics -Viruses are not considered alive as they do • • not have a metabolism or reproduce on their own. -Viruses are composed of DNA or RNA surrounded by a protein coat called a capsid. -If viruses are composed of RNA as their genetic material, they are called retroviruses Are Viruses Living or Non-living? • Viruses are both and neither • They have some properties of life but not others • For example, viruses can be killed, even crystallized like table salt • However, they can’t maintain a constant internal state (homeostasis). What are Viruses? • A virus is a noncellular particle made up of genetic material and protein that can invade living cells. II. Types of Viruses A. Bacteriophages •Viruses that attack bacteria are called bacteriophage or just phage •T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails T-phages •The most commonly studied T-phages are T4 and T7 •They infect E. coli , an intestinal bacteria •Six small spikes at the base of a contractile tail are used to attach to the host cell •Inject viral DNA into cell Diagram of T-4 Bacteriophage •Head with 20 triangular surfaces •Capsid contains DNA •Head & tail fibers made of protein B. Retroviruses Characteristics of Retroviruses •Contain RNA, not DNA •Contain enzyme called Reverse Transcriptase •When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell ENZYME Retroviruses cont… •HIV, the AIDS virus, is a retrovirus •Feline Leukemia Virus is also a retrovirus C. Viroids & Prions 1.Viroids •Small, circular RNA molecules without a protein coat •Infect plants •Potato famine in Ireland •Resemble introns cut out of eukaryotic 2. Prions •Prions are “infectious proteins” • They are normal body proteins that get converted into an alternate configuration by contact with other prion protein involved in human and mammalian prion proteins • They have no DNA or RNA •The main diseases is called “PrP” Prions cont…. •Prions form insoluble deposits in the brain •Causes neurons to rapidly degeneration. Ex. Mad cow disease (bovine spongiform encephalitis: BSE) is an example •People in New Guinea used to suffer from kuru, which they got from eating the brains of their enemies III Viral History Discovery of Viruses •Beijerinck (1897) coined the Latin name “virus” meaning poison •He studied filtered plant juices & found they caused healthy •plants to become sick Tobacco Mosaic Virus •Wendell Stanley (1935) crystallized sap from sick tobacco plants •He discovered viruses were made of nucleic acid and protein Smallpox •Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses •Deadly viruses are said to be virulent •Smallpox has been eradicated in the world today IV. SIZE of Viruses •Viruses are smaller than the smallest cell •Measured in nanometers •Viruses couldn’t be seen until the electron microscope was invented in the 20th century V.Viral Reproduction: 1. LYTIC CYCLE -a virus enters a cell and makes copies of itself that results in the immediate destruction of the host cell as it LYSES or BURSTS. 5 Steps of Lytic Cycle • 1. Attachment to the cell • 2. Penetration (injection) of viral DNA or RNA • 3. Replication (Biosynthesis) of new viral proteins and nucleic acids • 4. Assembly (Maturation) of the new viruses • 5. Release of the new viruses into the environment (cell lyses) Lytic Cycle Review • Attachment • Penetration • Biosynthesis • Maturation • Release Phage attaches by tail fibers to host cell Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell Production of phage DNA and proteins Assembly of phage particles Phage lysozyme breaks cell wall Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath 1 Attachment: Phage attaches to host cell. Tail fiber Base plate Pin Cell wall Tail Plasma membrane 2 Penetration: Phage pnetrates host cell and injects its DNA. Sheath contracted Tail core 3 Merozoites released into bloodsteam from liver may infect new red blood cells Tail DNA 4 Maturation: Viral components are assembled into virions. Capsid 5 Release: Host cell lyses and new virions are released. Tail fibers 2. Lysogenic Cycle •Phage DNA injected into host cell •Viral DNA joins host DNA forming a prophage •When an activation signal occurs, the phage DNA starts replicating Lysogenic Cycle •Viral DNA (part of prophage) may stay inactive in host cell for long periods of time •Replicated during each binary fission •Over time, many cells form containing the prophages The Lysogenic Cycle Viral Latency •Once a prophage cell is activated, host cell enters the lytic cell •New viruses form a & the cell lyses (bursts) •Virus said to be virulent (deadly) ACTIVE STAGE INACTIVE STAGE Viral Latency •Some viruses have the ability to become dormant inside the cell •Called latent viruses •They may remain inactive for long periods of time (years) •Later, they activate to produce new viruses in response to some external signal •HIV and Herpes viruses are examples Virulent Viruses HOST CELL LYSES & DIES Virulence VIRUS DESTROYING HOST CELL Lytic and Lysogenic Cycles copyright cmassengale 47 Viral Disease Like bacteria, viruses also can cause disease by disrupting the body’s normal equilibrium. Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola Some viruses may cause some cancers like leukemia - Herpes Virus SIMPLEX I and II Adenovirus COMMON COLD Influenza Virus Treatment for Viral Disease Unlike bacterial diseases, antibiotics do NOT work on viruses. -A vaccine can be used to prevent a viral disease. Vaccines • An attenuated virus is a weakened, less vigorous virus • “Attenuate" refers to procedures that weaken an agent of disease (heating) • A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus • Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness Other Viral Treatments •Interferon are naturally occurring proteins made by cells to fight viruses •Genetic altering of viruses (attenuated viruses) •Antiviral drugs (AZT) •Protease inhibitors – prevent capsid formation