Chapter 19 Bacteria and Viruses

Bacteria are prokaryotes Recently prokaryotes were split into two different groups; eubacteria and archaebacteria

Eubacteria: a very wide range of prokaryotes that can live almost anywhere 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

Archaebacteria: many live in very harsh environments They lack the carb in their cell wall that eubacteria have Their DNA is also more like eukaryotes than the DNA of eubacteria

Prokaryotes are identified by things like shape, their cell wall, movement, and they way they get energy There are 3 main bacteria shapes; bacilli (rod-shaped), cocci (spherical), and spirilla (corkscrew-shaped)

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 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

Some prokaryotes do not move, some are propelled by flagella, some spiral forward, some slide along in slime they secrete Most prokaryotes are heterotrophs, but some are autotrophs 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

Some bacteria need oxygen, while others are killed by it Obligate aerobes must have oxygen Obligate anaerobes cannot live with oxygen Facultative anaerobes can live with or without oxygen

Bacteria can grow and reproduce in different ways Binary fission = when a bacterium has grown large enough that it can replicate its DNA and split in two Conjugation = when a hollow bridge forms between 2 bacteria so they can exchange genetic info

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

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…

19-2: Viruses

Viruses are particles of nucleic acid, protein, and sometimes lipids Viruses can reproduce only by infecting living cells They vary in terms of shape and size

A typical virus is composed of a core of DNA and RNA surrounded by a protein coat Capsid = the protein coat The proteins bind to the host cell and trick the cell into letting it in Once the viral DNA is inside the cell it uses transcription and translation to create more proteins

Bacteriophages only infect bacteria Most viruses are very specific to the type of cell they will infect

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 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

A retrovirus contains RNA as its genetic code 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

Retroviruses can cause some types of cancer in animals The virus that causes AIDS is a retrovirus

Comparison of viruses and bacteria 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 DNA Growth and development No Yes Obtain and use energy Response to environment Change over time

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

Diseases caused by Bacteria and Viruses 19-3: Diseases caused by Bacteria and Viruses

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 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

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.

Other examples of bacterial infections are lyme disease, tetanus, bacterial meningitus, and tooth decay Many bacterial diseases can be prevented with vaccines Antibiotics can be used to treat bacterial infections that have already occurred

Bacterial diseases can be seen in animals – many bacteria can affect both humans and animals There are various methods used to control bacterial growth, including sterilization, disinfectants, and food processing Ex. Anthrax

Like bacteria, viruses produce disease by disrupting the body’s normal equilibrium 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

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

Many viruses infect plants and cause serious threats to agricultural crops - ex. Tobacco mosaic virus and potato yellow dwarf virus