Bacteria and Viruses

Chapter 18

Bacteria

Prokaryotes-single-celled organisms without an nucleus

Two kingdomsEubacteria-live anywhere; cell wall of

peptidoglycanArchaebacteria-live in extreme

environments; no peptidoglycan; most live without oxygen

Prokaryotes

Identified byShape

Cocci-roundSpirilli-spiral shapedBacilli-rod

Chemical nature of cell wallsThick peptidoglycan stains purple; thin walls

stain pinkMovement: flagella, twisting, secretionsMethod of obtaining energy

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Typical Bacteria Cell

Metabolic diversity

HeterotrophsChemoheterotrophs-take in organic

chemicals for energy and carbonPhotoheterotrophs-photosynthesize for

energy but take in chemicals for carbonAutotrophs

Photoautotrophs-use light for energy and carbon

Chemoautotrophs-use chemicals for energy and carbon

Releasing energy

Occurs by cell respiration, fermentation, or both

Obligate aerobes-require oxygen for survival

Obligate anaerobes-do not need oxygen and are often killed in oxygen

Facultative anaerobes-can live with or without oxygen

Bacterial reproduction

Binary fission-1.cell doubles in size; 2.replicates its DNA; 3.cell divides in half to make 2 new cells (identical)

Conjugation-1.one bacterium hooks to another bacterium with a pilus; 2. genes are exchanged between the two cells

Spore formation-thick coverings or endospores form to protect the bacterium in unfavorable conditions

Importance of bacteria

Help maintain the living worldDecomposers-recycle nutrients in the

environment (decaying organisms, sewage)

Nitrogen fixers-convert gaseous nitrogen to a useable form

Industrial uses-used to make food products, remove waste, digest petroleum, mine minerals

Viruses

Particles of nucleic acid, protein, and sometimes lipids

Reproduce only by infecting other cells

Differ in size and structureHighly specific in cells they infect

Typical virus structure

Capsid- protein coat, includes proteins that enable virus to enter a host cell

Nucleic acid core- made of DNA or RNA but not both

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Influenza Virus

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T4 Virus

Viral infection: Lytic

1. virus attaches to outside of cell and inserts its nucleic acid into the host

Viral DNA destroys host DNA and takes over the cells metabolism

Host is used to make new viral particles, DNA and protein

Host bursts open to release new viruses

Viral infection: Lysogenic

1. virus attaches to host and inserts its nucleic acid

Viral DNA is inserted into the host DNA and is replicated with host DNA for an unlimited amount of time

Viral DNA removes itself from host DNA and destroys host DNA

New viral particles are producedCell bursts open and releases new

viruses

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Retroviruses

Contain only RNAAfter infection, produce a DNA copy

of their RNADNA is inserted into host DNACan be dormant for unlimited

amount of timeIncludes some cancers and HIV

Viruses are NOT alive

Viruses must infect another cell in order to reproduce

Use host’s respiration, nutrition, and other functions

Are parasites

Diseases

Pathogens-disease causing agentsDisease – conflict between the

pathogen and the host; results when infection causes harm to the host; interferes with the host’s ability to obtain nutrients and energy needed to function properly

Bacterial disease in humans

First discovered by Louis PasteurSome bacteria damage cells and

tissues directlySome bacteria release toxins that

travel through the blood then damage tissues

Preventing bacterial disease

Vaccines-preparation of weakened or killed pathogens that is injected into the body to stimulate the immune system

Antibiotics-compounds that block the growth and reproduction of bacteria

Controlling bacteria

Sterilization by heat-destroys most bacteria since most cannot survive at high temperatures

Disinfectants- chemicals used to kill bacteria

Food preparation and storage-canning or using preservatives such as salt, sugar, pickling

Antibacterials

Added to most soaps and cleaning agents

Becoming problematicAllowing many bacteria to become

resistant to antibacterial agentsMakes bacteria harder to kill with

medications

Viral disease

Disrupt normal equilibrium in the cells

Specific to species they infectOnly be prevented with vaccines

before infection

Viroids

Single-stranded RNA molecules with no capsid

Enter cell and direct synthesis of new viroids

Infect plants and disrupt metabolism, stunt growth

Prions

Protein-infectious particlesCause disease by forming protein

clumps which induce normal proteins to become prions

Damage nerve tissue and cellsMad-cow disease; Creutzfeldt-Jakob

in humans