VirusesObjectivesIdentify different types of virusesCompare replication cycles Discuss how viruses cause disease

The Viruses• Viruses are noncellular and thus cannot be

classified with cellular organisms• Generally smaller than 200 nm in diameter• Usually named after the diseases they cause

3

Viral Structure• Each type has at least two parts

– Capsid: Outer layer composed of protein subunits• Some enveloped by membrane• Others “naked”

– Nucleic acid core: DNA or RNA

• Vary in shape from thread-like to polyhedral

Virus Structure

7

Parasitic NatureViruses are:

Obligate intracellular parasites Cannot reproduce outside a living cell

Can be cultured only inside living cells Chicken egg Tissue culture

Most are host specific

8

Viral CategorizationClassification is based on:

Type of nucleic acidSize and shapePresence / absence of outer envelope

9

The Bacteriophages:ReproductionBacteriophages – Viruses that infect bacterial

cellsPortions of capsid adhere to specific receptor

on the host cellViral nucleic acid enters the cellOnce inside, the virus takes over metabolic

machinery of the host cell

10

Bacteriophages:The Lytic CycleLytic cycle may be divided into five stages:

AttachmentPenetrationBiosynthesisMaturationRelease

Kills the host cell

11

The Bacteriophages:The Lysogenic CyclePhage becomes a prophage (provirus)

Becomes integrated into the host genomeBecomes latent

May later reenter the lytic cycle

Doesn’t kill the host (at first anyway)Disease causing viruses

Herpes simplex I (cold sores) and II (genital herpes), and hepatitis B, chicken pox (shingles)

13

Reproduction of Animal VirusesAnimal virus enters the host cellUncoating releases viral DNA or RNA

Budding: Viral particles released in a bud Acquires a membranous envelopeExamples:

Retroviruses (HIV >>>>AIDS) Contain reverse transcriptase Carries out RNA cDNA reverse transcription cDNA becomes integrated into host DNA

15

16

Viral Infections• Viruses are best known for causing

infectious diseases in plants and animals• Examples:– Herpes, HIV, cancer• Viruses lack metabolism; thus, antibiotics have no

effect– Viroids• Naked strands of RNA• Many crop diseases

– Prions• Protein molecules with contagious tertiary structure• Some human and other animal diseases - Mad cow

disease

17

Diseases caused by viruses:In HumansCold/fluMeaslesHerpespolioSmallpox

WartsHIVmononucleosis

In AnimalsDistemperFoot and Mouth diseaseFeline LeukemiaIn PlantsTobacco Mosaic Disease

Control of VirusesWhite Blood Cells in humans

AntibodiesInterferon (chemical produced in the body)

Vaccines

Examples of Viruses

18-2 Archaebacteria and EubacteriaObjectivesCompare types of ProkaryotesExplain the characteristics and adaptations of

bacteriaEvaluation the economic importance of

bacteria

23

The ProkaryotesInclude eubacteria and archaeabacteria,

which are fully functioning cellsA single spoonful of earth can contain >1000

prokaryotesRange in size from 1-10 µm in length and 0.7-

1.5 µm in width

24

Prokaryote StructureCharacteristics:• Lack a membrane-bounded nucleus (DNA in

nucleoid region)• Outer cell wall containing peptidoglycan• Some move by means of flagella• Lack membranous organelles• May have accessory ring of DNA (plasmid)

26

27

Reproduction in ProkaryotesAsexual

Prokaryotes reproduce asexually by means of binary fission

Methods of genetic recombinationConjugation

Sex pilus forms between two cellsDonor cell passes DNA to recipient cell through pilus

Transformation – taking up pieces of DNA secreted by live bacteria or released by dead bacteria

Transduction-transfer of portions of bacterial DNA from one cell to another

28

29

30

Reproduction in ProkaryotesSome bacteria form resistant endospores

under unfavorable conditions

31

32

Prokaryotic NutritionOxygen requirements:

Obligate aerobes – unable to grow in the absence of free oxygen

Obligate anaerobes – unable to grow in the presence of free oxygen

Facultative anaerobes – able to grow in either the presence or absence of free oxygen

33

34

The Bacteria (eubacteria)Bacteria are commonly diagnosed using the

Gram stain procedureWhen washed after staining:

Gram-positive bacteria retain dye and appear purple

Gram-negative bacteria do not retain dye and appear pink

35

The BacteriaStructure of cell wall also of diagnostic useBacteria can be further classified in terms of

their three basic shapesSpiral (spirilli),Rod (bacilli), andRound (cocci)

36

37

CyanobacteriaFormerly called the Blue-Green algae

(Cyanophyta)Cyanobacteria are Gram-negative bacteria

that photosynthesize*Believed to be responsible for introducing

oxygen into the primitive atmosphereLack visible means of locomotionCan live in extreme environmentsWhen commensals with fungi, form lichens

38

39

The ArchaeaArchaea were earlier considered bacteria their rRNA differs from BacteriaOther differences:

cell walls

40

Archaea Metabolism• Most are chemoautotrophs• Some mutualistic• Some commensalistic• None known to be parasitic• None are photosynthetic• Many live in harsh conditions

41

Many live in harsh conditions:Anaerobic marshes

MethanogensProduce methane from hydrogen gas and

carbon dioxideSalty lakes

HalophilesRequire high salt concentrations for growth

Types of Archaea

Hot sulfur springsThermoacidophilesReduce sulfides and survive best at

temperatures above 80ºCPlasma membranes contain unusual lipids

convey tolerance of high temperatures

Other Facts about bacteriacan cause disease

(Pneumonia, Strep. throat, TB, food poisoning, syphilis, gonorrhea…)

44

Control of harmful bacteriasome can be destroyed or growth slowed with high temps, chemicals, steam, cold, antisepticssterilization, sanitation, pasteurization

Bacteria can be beneficialDecomposition or recycling of nutrients

Digestion (vitamins)make breads, beers, and wineantibiotics food texture (yogurt, cheeses)genetic engineering – insulinNitrogen fixation

Borrelia burgdorferiStaphylococcus