chapter 19 bacteria and viruses 19-1: bacteria. recently prokaryotes were split into two different...
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Chapter 19 Bacteria and Viruses
19-1: Bacteria
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Recently prokaryotes were split into two different groups; eubacteria and archaebacteria
Bacteria are prokaryotes
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They have a cell wall for protection – the wall contains a carbohydrate for extra support
Some even have another membrane that sits outside the cell membrane
Eubacteria: a very wide range of prokaryotes that can live almost anywhere
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They lack the carb in their cell wall that eubacteria have
Archaebacteria: many live in very harsh environments
Their DNA is also more like eukaryotes than the DNA of eubacteria
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There are 3 main bacteria shapes; bacilli (rod-shaped), cocci (spherical), and spirilla (corkscrew-shaped)
Prokaryotes are identified by things like shape, their cell wall, movement, and they way they get energy
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Gram positive appears purple and means the cell wall has the carb
Gram negative appears pink and means the cell wall doesn’t have the carb
There are 2 different types of cell walls; a Gram stain can be used to tell them apart
A Gram stain test uses 2 different dyes to tell if the cell wall contains a specific carbohydrate
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Photoautotrophs use light energy to make they energy the need (almost like plants)
Chemoautotrophs use carbon molecules from carbon dioxide to make the energy they need
Most prokaryotes are heterotrophs, but some are autotrophs
Some prokaryotes do not move, some are propelled by flagella, some spiral forward, some slide along in slime they secrete
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Obligate aerobes must have oxygen
Obligate anaerobes cannot live with oxygen
Some bacteria need oxygen, while others are killed by it
Facultative anaerobes can live with or without oxygen
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Conjugation = when a hollow bridge forms between 2 bacteria so they can exchange genetic info
Bacteria can grow and reproduce in different waysBinary fission = when a bacterium has grown large enough that it can replicate its DNA and split in two
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Bacteria can form spores bacteria DNA gets surrounded by a thick cell wall
Spores can lay dormant until conditions are favorable for more growth – this lets bacteria survive harsh conditions
Anthrax
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While we tend to think of bacteria as a bad thing, many bacteria are very useful
Uses include decomposition, nitrogen fixation, food production, helping humans produce vitamins, digestion of oil and poison, etc…
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19-2: Viruses
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They vary in terms of shape and size
Viruses are particles of nucleic acid, protein, and sometimes lipids
Viruses can reproduce only by infecting living cells
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Capsid = the protein coat
The proteins bind to the host cell and trick the cell into letting it in
A typical virus is composed of a core of DNA and RNA surrounded by a protein coat
Once the viral DNA is inside the cell it uses transcription and translation to create more proteins
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Most viruses are very specific to the type of cell they will infect
Bacteriophages only infect bacteria
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In a lysogenic infection, a virus integrates its DNA into the DNA of the host cell, and the viral genetic info replicates along with the host cell DNA
Once a virus is inside a cell, two things can happen
In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst
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Once a retrovirus enters a cell, it makes a DNA copy of its RNA
The new DNA gets inserted into the DNA of the host cell and can stay dormant for some time
A retrovirus contains RNA as its genetic code
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Retroviruses can cause some types of cancer in animals
The virus that causes AIDS is a retrovirus
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Characteristic Virus Cells (bacteria and others)
Structure DNA or RNA core, capsid
Cell membrane, cytoplasm
Reproduction Only within a host cell
Independent cell division
Genetic Code DNA or RNA DNAGrowth and development
No Yes
Obtain and use energy
No Yes
Response to environment
No Yes
Change over time Yes Yes
Comparison of viruses and bacteria
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Viruses are not considered living even though they have many characteristics of living things
Viruses are considered parasites since they must infect a living cell to grow and reproduce
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19-3: Diseases caused by
Bacteria and Viruses
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Some bacteria damage cells and the tissues of the infected organism directly by breaking down the cells for food
Ex. The bacterium that causes tuberculosis is inhaled into the lungs and destroys lung tissue
Bacteria produce disease in one of two general ways
Some bacteria damage cells and the tissues of the infected organism directly by breaking down the cells for food
Ex. The bacterium that causes tuberculosis is inhaled into the lungs and destroys lung tissue
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Other bacteria release toxins that travel throughout the body interfering with the normal activity of the host
Ex. The bacterium that causes strep throat releases toxins in the bloodstream these can even cause scarlet fever.
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Many bacterial diseases can be prevented with vaccines
Antibiotics can be used to treat bacterial infections that have already occurred
Other examples of bacterial infections are lyme disease, tetanus, bacterial meningitus, and tooth decay
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There are various methods used to control bacterial growth, including sterilization, disinfectants, and food processing
Bacterial diseases can be seen in animals – many bacteria can affect both humans and animals
Ex. Anthrax
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In many viral infections, viruses attack and destroy certain cells in the body
Examples include the common cold, influenza, smallpox, AIDS, chickenpox, measles, and west nile
Like bacteria, viruses produce disease by disrupting the body’s normal equilibrium
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Viral diseases CANNOT be treated with antibiotics
The best way to protect against viral infections is with vaccines
Viruses can produce serious animal diseases also
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Many viruses infect plants and cause serious threats to agricultural crops - ex. Tobacco mosaic virus and potato yellow dwarf virus