Chapter 19 Bacteria and Viruses. 19-1 Bacteria The invention of the microscope opened our eyes to...
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Transcript of Chapter 19 Bacteria and Viruses. 19-1 Bacteria The invention of the microscope opened our eyes to...
Chapter
19Bacteria and Viruses
19-1 Bacteria• The invention of the microscope
opened our eyes to the hidden, living world around us
• Microscopic life covers nearly every square centimeter of Earth
Prokaryotes
• The smallest and most common microorganisms
• Unicellular organisms that lack a nucleusand membrane bound organelles
• bacteria
Classifying Prokaryotes• Until recently, all prokaryotes were
placed in a single kingdom - monera• More recently, biologists have
begun to appreciate that prokaryotes can be divided into two very different kingdoms: the eubacteriaand the archaebacteria
Eubacteria• Eubacteria include a wide range
of organisms with different lifestyles
• Eubacteria live almost everywhere
Archaebacteria• Lack the same carbohydrates of
eubacteria and also have different membrane lipids
• Also, the DNA sequences of key archaebacterial genes are more like those of eukaryotes than those of eubacteria
• Many archaebacteria live in extremely harsh environments
Identifying Prokaryotes• Prokaryotes are identified by
characteristics such as shape, the chemical nature of their cell walls, the way they move and the way they obtain energy
Shapes• Bacilli – rod shaped
• Cocci – spherical shaped
• Spirilla – spiral and corkscrew shaped
Cell Walls• Eubacteria – have peptigoglycan
• Archaebacteia – don’t have peptigoglycan
Movement• Some bacteria move differently
than others
Metabolic Diversity• No characteristic of prokaryotes
illustrates their diversity better than the way they obtain energy
Heterotrophs
• Must take inorganic molecules for both energy and a supply of carbon
Photoheterotrophs• These organisms are
photosynthetic using sunlight for energy but they also need to take in organic compounds as a carbon source
Photoautotrophs
• Use light energy to convert carbon dioxide and water to carbon compounds and oxygen in a process similar to that used by green plants
Ex.) cyanobacteria (blue-green algae)
Chemoautotrophs • Can perform chemosynthesis
• Make organic carbon molecules from carbon dioxide
• Unlike photoautotrophs, however they do not require light as a source of energy. Instead they use energy directly from chemical reactions
Releasing Energy• Like all organisms, bacteria need
a constant supply of energy
• This energy is released by the process of cellular respiration or fermentation or both
Obligate aerobes • Require a constant supply of
oxygen in order to live
Obligate anaerobes • Do not require oxygen and if fact
may be killed by it
Facultative anaerobes • Can survive with or without
oxygen
Growth and Reproduction
• Bacteria can grow really fast
• If unlimited space and food were available to a single bacterium and if all of its offspring divided every 20 minutes in just 48 hours they would reach a mass of approximately 4000 times the mass of the earth!
Binary Fission• When a bacterium has grown so
that it has nearly doubled in size, it replicates its DNA and divides in half producing 2 identical daughter cells
Binary Fission
• Bacterial reproduction, asexual reproduction
Conjugation• Many bacteria are also able to
exchange genetic information by a process called conjugation
• This transfer of genetic information increases genetic diversity
Spore Formation• When growth conditions become
unfavorable, many bacteria form structures called spores
Endospore
• A type of spore formed when a bacterium produces a thick internal wall that encloses a thick internal wall that encloses its DNA and a portion of its cytoplasm
Endospore
Importance of Bacteria• Bacteria are vital to maintaining the
living world• Some are producers that capture
energy by photosynthesis• Others are decomposers that break
down the nutrients in dead matter and the atmosphere
• Still other bacteria have human uses
Decomposers• As decomposers, bacteria help
the ecosystem recycle nutrients, therefore maintaining equilibrium in the environment
Nitrogen Fixers• You may recall that plants need nitrogen to
make amino acids, the building blocks of protiens
• Nitrogen gas (N2) makes up approximately 78 percent of Earth’s atmosphere
• However, plants can’t use nitrogen gas directly
• Nitrogen must first be changed chemically to ammonia (NH3) or other nitrogen compounds
Nitrogen fixation • Process which turns unusable nitrogen
gas into useful nitrogen containing compounds
• Allows nitrogen atoms to continually cycle through the biosphere
• Many plants have symbiotic relationships with nitrogen fixing bacteria
Human Uses of Bacteria• Used in food and beverage
production• Industries: petroleum, water,
mining, drugs• Inside of us (symbiosis)
–E.coli
• Drug research
19 – 2 Viruses
Viruses• Particles of nucleic acid, protein, and
sometimes lipids
• Viruses can reproduce only by infecting living cells
• A typical virus is composed of a core of DNA or RNA surrounded by a protein coat
• Viruses are very small. They can only be seen with an electron microscope
Capsid • A viruses protein coat
• The capsid proteins of a typical virus bind to receptors on the surface of a cell and “trick” the cell into allowing it inside
• Once inside, the viral genes are expressed and causes the host cell to make copies of the virus and in the process the host cell is destroyed
• Because viruses must bind precisely to proteins on the cell surface and then use a hosts genetic system, most viruses are highly specific to the cells they infect
Viral Infection• Once the virus is inside the host
cell, two different processes may occur
Lytic Infection• In a lytic infection, a virus enters a
cell, makes copies of itself, and causes the cell to burst
A literary approach to lytic virus infections
In its own way, a lytic virus is similar to a desperado in the Old West. First, the outlaw eliminates the town’s existing authority (host cell DNA). Then, the desperado demands to be outfitted with new weapons, horses, and riding equipment by terrorizing the local people (using the host cell to make proteins). Finally, the desperado forms a gang that leaves the town to attack new communities (the host cell bursts, releasing hundreds of virus particles).
Lysogenic Infection• In a lysogenic infection, a virus integrates its
DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cells DNA
• Unlike lytic viruses, lysogenic viruses do not lyse the host cell right away. Instead, a lysogenic virus remains inactive for a period of time
• Eventually, only one of a number of factors may activate the DNA of a prophage which will then remove itself from the host cell DNA and direct the synthesis of new viruses particles
Retroviruses• Viruses that contain RNA as their
genetic information
• When retroviruses infect a cell, they produce a DNA copy of their RNA
• Ex.) Human Immunodeficiency Virus (HIV) and Feline leukemia virus
Viruses and Living Cells• Viruses must infect a living cell in
order to grow and reproduce• They also take advantage of the
host’s respiration, nutrition and all the other functions that occur in living things
• Therefore, viruses are considered to be parasites
Parasites • organisms that live on or in a host
organism from which it obtains nutrients, and it usually does harm to the host
Cells and VirusesCharacteristic Cell Virus
Structure Cell membrane, cytoplasm; eukaryotes also contain nucleus and organelles
Reproduction Independent cell division either asexually or sexually
Genetic Code DNA
Growth and Development Yes; in multicellular organisms, cells increase in number and differentiate
Obtain and Use Energy yes
Response to Environment yes
Change Over Time yes
Are viruses alive?
19 – 3 Diseases Caused by Bacteria and Viruses
• Bacteria and viruses are everywhere in nature, but only a few cause disease
Pathogens • Disease causing agents
• All viruses reproduce by infecting living cells, and disease results when the infection causes harm to the host
• All bacteria require nutrients and energy: however, disease results when bacteria interfere with the host’s ability to obtain enough of those elements to function properly
Bacterial Disease in Humans• Bacteria produce disease in one of
two general ways
1. Some bacteria damage the cells and tissues of the host by breaking down the cells for food
2. Other bacteria release toxins that travel throughout the body interfering with the normal activity of the host
Preventing Bacterial Disease
• Many bacterial disease can be prevented by stimulating the bodies immune system with vaccines
Vaccine • A preparation of weakened or killed
pathogen
• When injected into the body, a vaccine sometimes prompts the body to produce immunity to the disease
• If a bacterial infection does occur, a number of drugs can be used to attack and destroy the invading bacteria
Antibiotics
• Compounds that block the growth and reproduction of bacteria NOT virus
Controlling Bacteria• There are various methods used
to control bacterial growth, including sterilization, disinfectants, and food processing
Sterilization by Heat• Many bacteria cannot survive
high temperatures for a long time, so most can be killed by exposure to high heat
• Ex.) pasteurization
Disinfectants • Chemical solutions that kill
pathogenic bacteria (chlorine)
Food Storage and Processing
• Food that is stored at a low temperature will stay fresh longer because bacteria cannot reproduce fast at cold temperatures
• Also, a lot of the processing procedures that are used in the food industry raise the temperature of food to a point where the bacteria are killed
Viral Disease in Humans• Like bacteria, viruses produce
disease by disrupting the body’s normal equilibrium
• Unlike bacterial diseases, viruses can’t be treated with antibiotics
• The best way to protect against most viral diseases lies in prevention by the use of vaccines
Viral Disease in Animals• Viruses produce serious animal diseases
Ex.) Foot-and-mouth disease, Rous sarcoma
Viral Disease in Plants• Many viruses infect plants
• Ex.) Tobacco mosaic virus, potato yellow dwarf virus
Viroids and Prions• Scientists have discovered two
virus-like particles that also cause disease
Viroids• Single stranded RNA molecules
that have no surrounding capsid
• Cause disease in plants
Prions• Proteins that cause disease in animals
Ex.) Mad cow disease