Bacteria and VirusesBacteria and Viruses

Ch. 19Ch. 19

Page 470Page 470

Bacteria 19-1Bacteria 19-1

Bacteria are Bacteria are prokaryotesprokaryotes

That is, they That is, they contain no nucleuscontain no nucleus

Classifying bacteriaClassifying bacteria

Eubacteria are organisms Eubacteria are organisms like like EscherichiaEscherichia colicoli, or , or E. coliE. coli

They contain a cell wall that They contain a cell wall that contains a carbohydrate contains a carbohydrate known as peptidoglycanknown as peptidoglycan

ArchaebacteriaArchaebacteriaArchaebacteria lack the Archaebacteria lack the peptidoglycan of Eubacteria peptidoglycan of Eubacteria and also have different and also have different membrane lipidsmembrane lipids

The DNA sequence is also The DNA sequence is also more like those of more like those of EukaryotesEukaryotes

Identifying prokaryotesIdentifying prokaryotes

They are identified by shape, They are identified by shape, cell wall composition, cell wall composition, movement, and the way they movement, and the way they obtain energyobtain energy

Shape: Bacilli – Rod-shaped Shape: Bacilli – Rod-shaped bacteria; Spirilla – Spiral and bacteria; Spirilla – Spiral and corkscrew shaped bacteriacorkscrew shaped bacteria

Identifying prokaryotesIdentifying prokaryotesCell walls – Bacteria that are gram Cell walls – Bacteria that are gram

positive have a thick positive have a thick peptidoglycan layer; Bacteria that peptidoglycan layer; Bacteria that are gram negative have thinner are gram negative have thinner wallswalls

Movement- Some prokaryotes do Movement- Some prokaryotes do not move at all, others are not move at all, others are propelled by flagella, whip-like propelled by flagella, whip-like structures used for movementstructures used for movement

MetabolismMetabolism Most prokaryotes are heterotrophs, Most prokaryotes are heterotrophs,

some are autotrophssome are autotrophs Most heterotrophic prokaryotes must Most heterotrophic prokaryotes must

take in organic compounds for food; take in organic compounds for food; they are known as they are known as chemoheterotrophs.chemoheterotrophs.

Humans are also chemoheterotrophs Humans are also chemoheterotrophs which means we compete with some which means we compete with some prokaryotes for food!prokaryotes for food!

Metabolism-cont.Metabolism-cont.

Photoheterotrophs are Photoheterotrophs are prokaryotes that are prokaryotes that are both photosynthetic (use both photosynthetic (use sunlight for energy) and sunlight for energy) and take in their food.take in their food.

Metabolism-contMetabolism-contAutotrophsAutotrophsPhotoautotrophs- use light energy Photoautotrophs- use light energy

to convert carbon dioxide and to convert carbon dioxide and water to carbon compounds; water to carbon compounds; similar to plants.similar to plants.

Chemoautotrophs- Make organic Chemoautotrophs- Make organic compounds from carbon dioxide. compounds from carbon dioxide. They do not use light energy, they They do not use light energy, they use chemical reactions as energy.use chemical reactions as energy.

Releasing energyReleasing energy Obligate aerobes are organisms that Obligate aerobes are organisms that

require a constant supply of oxygen require a constant supply of oxygen to live. Ex. to live. Ex. Mycobacterium Mycobacterium tuberculosistuberculosis

Obligate anaerobes do not need Obligate anaerobes do not need oxygen, and in fact may be killed by oxygen, and in fact may be killed by it! Ex. it! Ex. Clostridium botulinumClostridium botulinum

Facultative anaerobes can survive Facultative anaerobes can survive with or without oxygen. with or without oxygen. E. coliE. coli

Growth and ReproductionGrowth and Reproduction

Binary fission is a type of asexual Binary fission is a type of asexual reproduction in which bacteria reproduction in which bacteria form two identical daughter cells.form two identical daughter cells.

Conjugation involves the Conjugation involves the formation of a hollow bridge formation of a hollow bridge between bacteria and movement between bacteria and movement of genes from one cell to anotherof genes from one cell to another

Growth and Reprodcution-Growth and Reprodcution-contcont

Spore formation occurs when Spore formation occurs when growing conditions are growing conditions are unfavorable for bacteriaunfavorable for bacteria

A thick wall encloses the bacterial A thick wall encloses the bacterial DNA and part of its cytoplasm.DNA and part of its cytoplasm.

Spores can wait for months and Spores can wait for months and even years for conditions to even years for conditions to improve before they germinate.improve before they germinate.

Importance of BacteriaImportance of Bacteria

Bacteria are vital to Bacteria are vital to maintaining the living maintaining the living world.world.

Some are producersSome are producersSome are decomposersSome are decomposersOthers have human usesOthers have human uses

Importance of Bacteria-contImportance of Bacteria-contDecomposers help maintain Decomposers help maintain

equilibrium in the environment by equilibrium in the environment by recycling nutrients in an ecosystem.recycling nutrients in an ecosystem.

Nitrogen fixers such as the Nitrogen fixers such as the bacterium bacterium RhizobiumRhizobium convert convert nitrogen gas into ammonia, a nitrogen gas into ammonia, a useable form for plants.useable form for plants.

Human uses- E.coli in our intestine Human uses- E.coli in our intestine makes vitamins for us that we makes vitamins for us that we cannot make ourselves.cannot make ourselves.

VirusesViruses

A virus is composed of DNA A virus is composed of DNA or RNA surrounded by a or RNA surrounded by a protein coatprotein coat

The protein coat is called a The protein coat is called a capsidcapsid

A bacteriophage is a virus A bacteriophage is a virus that attacks bacteriathat attacks bacteria

Viral InfectionViral InfectionLytic infection – In a lytic Lytic infection – In a lytic

infection, a virus enters a cell, infection, a virus enters a cell, makes copies of itself, and causes makes copies of itself, and causes the cell to burstthe cell to burst

Lysogenic infection – A virus Lysogenic infection – A virus integrates its DNA into the DNA of integrates its DNA into the DNA of the host cell, and the viral genetic the host cell, and the viral genetic information replicates along with information replicates along with the host cell’s DNA.the host cell’s DNA.

Viral infectionViral infection

The viral DNA that The viral DNA that is embedded in the is embedded in the host cell’s DNA is host cell’s DNA is called a prophage.called a prophage.

RetrovirusesRetroviruses

Retroviruses contain RNA as Retroviruses contain RNA as their genetic informationtheir genetic information

They get their name from the They get their name from the fact that their genetic fact that their genetic information is copied backward, information is copied backward, that is from RNA to DNA.that is from RNA to DNA.

AIDS is a retrovirusAIDS is a retrovirus

Bacterial/Viral diseasesBacterial/Viral diseasesPathogens are disease Pathogens are disease causing agents.causing agents.

Bacteria produce disease in Bacteria produce disease in one of two ways: 1. They one of two ways: 1. They break down cells for food. 2. break down cells for food. 2. They release toxins that travel They release toxins that travel throughout the body and throughout the body and interfere with normal activityinterfere with normal activity

Preventing bacterial diseasePreventing bacterial disease

A vaccine is a preparation of killed A vaccine is a preparation of killed or weakened pathogens that or weakened pathogens that stimulates the body’s immune stimulates the body’s immune system to provide immunity to system to provide immunity to that disease. Ex. Polio vaccine.that disease. Ex. Polio vaccine.

Antibiotics are compounds that Antibiotics are compounds that block the growth and reproduction block the growth and reproduction of bacteria. Ex. Penicillinsof bacteria. Ex. Penicillins

Bacterial diseases in Bacterial diseases in AnimalsAnimalsAnthrax is a disease that is Anthrax is a disease that is

deadly and can be passed from deadly and can be passed from animals to mananimals to man

It forms spores and is tough to It forms spores and is tough to kill.kill.

It has been used as a biological It has been used as a biological weaponweapon

Caused by Caused by Bacillus anthracisBacillus anthracis

Controlling bacteriaControlling bacteria

Methods to control bacterial Methods to control bacterial growth include heat sterilization, growth include heat sterilization, disinfectants, and food disinfectants, and food processingprocessing

Heat sterilization involves Heat sterilization involves subjecting bacteria to high subjecting bacteria to high temperatures for a prolonged temperatures for a prolonged period of timeperiod of time

DisinfectantsDisinfectants

Disinfectants are Disinfectants are chemical solutions that chemical solutions that kill pathogenic bacteriakill pathogenic bacteria

They include such things They include such things as soaps and cleansers.as soaps and cleansers.

Food storage/processingFood storage/processingStoring food in a refrigerator Storing food in a refrigerator

slows bacterial growth and slows bacterial growth and reproduction keeping food fresher reproduction keeping food fresher for a longer period of timefor a longer period of time

Canning keeps foods fresh almost Canning keeps foods fresh almost indefinitely. Food is sterilized indefinitely. Food is sterilized with high heat then placed in with high heat then placed in sterile containers and sealed.sterile containers and sealed.

Viral diseasesViral diseases

Viruses produce disease by Viruses produce disease by disrupting the body’s normal disrupting the body’s normal equilibriumequilibrium

Viral diseases cannot be Viral diseases cannot be treated with antibioticstreated with antibiotics

Prevention with vaccines is Prevention with vaccines is the best treatmentthe best treatment

Viroids and PrionsViroids and PrionsViroids are single-stranded RNA Viroids are single-stranded RNA

molecules with no capsid. They molecules with no capsid. They cause diseases in plants.cause diseases in plants.

Prions are “protein infectious Prions are “protein infectious particles” that cause diseases in particles” that cause diseases in animals by forming protein animals by forming protein clumps. Mad cow disease may be clumps. Mad cow disease may be caused by prions.caused by prions.