Chapter 19 Bacteria and Viruses

19-1: Bacteria

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

Bacteria are prokaryotes

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

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

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

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

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

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

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

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

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

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

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

Bacteriophages only infect bacteria

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

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

Retroviruses can cause some types of cancer in animals

The virus that causes AIDS is a retrovirus

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

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

19-3: Diseases caused by

Bacteria and Viruses

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

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.

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

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

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

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