Viruses Objectives Identify different types of viruses Compare 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 Nature Viruses 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 Categorization Classification is based on: Type of nucleic acid Size and shape Presence / absence of outer envelope 9

The Bacteriophages: Reproduction Bacteriophages – Viruses that infect bacterial cells Portions of capsid adhere to specific receptor on the host cell Viral nucleic acid enters the cell Once inside, the virus takes over metabolic machinery of the host cell 10

Bacteriophages: The Lytic Cycle Lytic cycle may be divided into five stages: Attachment Penetration Biosynthesis Maturation Release Kills the host cell 11

The Bacteriophages: The Lysogenic Cycle Phage becomes a prophage (provirus) Becomes integrated into the host genome Becomes 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 Viruses Animal virus enters the host cell Uncoating releases viral DNA or RNA Budding: Viral particles released in a bud Acquires a membranous envelope Examples: Retroviruses (HIV >>>>AIDS) Contain reverse transcriptase Carries out RNA  cDNA reverse transcription cDNA becomes integrated into host DNA 15

Reproduction of the Retrovirus HIV-1 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 Humans Cold/flu Measles Herpes polio Smallpox Warts HIV mononucleosis

In Animals Distemper Foot and Mouth disease Feline Leukemia In Plants Tobacco Mosaic Disease

Control of Viruses White Blood Cells in humans Antibodies Interferon (chemical produced in the body) Vaccines

Examples of Viruses

18-2 Archaebacteria and Eubacteria Objectives Compare types of Prokaryotes Explain the characteristics and adaptations of bacteria Evaluation the economic importance of bacteria

23 The Prokaryotes Include eubacteria and archaeabacteria, which are fully functioning cells A single spoonful of earth can contain >1000 prokaryotes Range in size from 1-10 µm in length and µm in width

24 Prokaryote Structure Characteristics: 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 Flagell a

27 Reproduction in Prokaryotes Asexual Prokaryotes reproduce asexually by means of binary fission Methods of genetic recombination Conjugation Sex pilus forms between two cells Donor 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 Fimbriae and Sex Pilus

29 Binary Fission

30 Reproduction in Prokaryotes Some bacteria form resistant endospores under unfavorable conditions

31 The Endospore of Clostridium tetani

32 Prokaryotic Nutrition Oxygen 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 Nodules of a Legume

34 The Bacteria (eubacteria) Bacteria are commonly diagnosed using the Gram stain procedure When washed after staining: Gram-positive bacteria retain dye and appear purple Gram-negative bacteria do not retain dye and appear pink

35 The Bacteria Structure of cell wall also of diagnostic use Bacteria can be further classified in terms of their three basic shapes Spiral (spirilli), Rod (bacilli), and Round (cocci)

36 Diversity of Bacteria

37 Cyanobacteria Formerly called the Blue-Green algae (Cyanophyta) Cyanobacteria are Gram-negative bacteria that photosynthesize *Believed to be responsible for introducing oxygen into the primitive atmosphere Lack visible means of locomotion Can live in extreme environments When commensals with fungi, form lichens

38 Diversity Among the Cyanobacteria

39 The Archaea Archaea were earlier considered bacteria their rRNA differs from Bacteria Other 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 Methanogens Produce methane from hydrogen gas and carbon dioxide Salty lakes Halophiles Require high salt concentrations for growth Types of Archaea

Hot sulfur springs Thermoacidophiles Reduce sulfides and survive best at temperatures above 80ºC Plasma membranes contain unusual lipids convey tolerance of high temperatures

Other Facts about bacteria can cause disease (Pneumonia, Strep. throat, TB, food poisoning, syphilis, gonorrhea…)

44 Thermoacidophile Habitat and Structure

Control of harmful bacteria some can be destroyed or growth slowed with high temps, chemicals, steam, cold, antiseptics sterilization, sanitation, pasteurization

Bacteria can be beneficial Decomposition or recycling of nutrients Digestion (vitamins) make breads, beers, and wine antibiotics food texture (yogurt, cheeses) genetic engineering – insulin Nitrogen fixation

Borrelia burgdorferi Staphylococcus