Unit 3 – Chapter 19

 Latin = “Poison”  A tiny disease-causing agent consisting of a core of nucleic acid, usually encased in protein.  Not cellular  Cannot move about on own  Cannot carry on metabolic activities independently  Pathogen – a disease causing agent

 Consist of a core of nucleic acid Contain either DNA or RNA (not both)  Surrounded by a protein coat Lack Ribosomes and enzymes necessary for protein production

 Classified according to common characteristics Type of nucleic acid Presence or absence of a protein coat  Does not use Linnaean system

 Escaped Gene Hypothesis Viruses were originally fragments of DNA or RNA that “escaped” from cellular organisms Some viruses may trace their origins to animal cells, plant cells, or bacterial cells May explain why each virus usually infect only certain ‘related’ species

 Viruses that attack/kill bacteria  AKA “Bacteria Eaters” or “phages”  Complex virus  Used to be used in place of antibiotics and sulfa drugs  They are making a comeback because of bacterial resistance to antibiotics Used to attach to bacteria

 Lytic Cycle vs. Lysogenic Cycle

 The life cycle of a virus that kills the host cell by lysing (destroying) it  Forces host cell to replicate viral particles by using its metabolic machinery 1. The virus attaches to receptors on the host cell wall 2. Nucleic acid of virus moves through plasma membrane and into the cytoplasm of the host cell 3. The protein coat remains on the outside exterior of the host cell 4. The virus uses the cell’s metabolic machinery to make new bacteriophage viruses 5. Bacterial cell lyses and releases many phages to infect other cells 6. Results in the death of the host cell

 The life cycle of a virus that kills the host cell by lysing (destroying) it  Forces host cell to replicate viral particles by using its metabolic machinery

1. The virus attaches to receptors on the host cell wall 2. Nucleic acid of virus moves through plasma membrane and into the cytoplasm of the host cell 3. The protein coat remains on the outside exterior of the host cell 4. The virus uses the cell’s metabolic machinery to make new bacteriophage viruses 5. Bacterial cell lyses and releases many phages to infect other cells 6. Results in the death of the host cell Fig. 19-2, p. 367

 Describe the Lytic Cycle.  What organisms does it occur in?

 Integrate their DNA into the host bacteria cells’ DNA  Does not destroy its host  Prophage – when viral nucleic acid is integrated with bacterial DNA  When bacterial DNA replicates, viral prophage replicates  Bacterial cells carrying prophages are called “lysogenic cells”  Can spontaneously turn to lytic

Fig. 19-3, p. 368 Lysogenic Cycle

NOYES  Not cellular  A cell is “the basic unit of life”  By itself, a virus can do nothing It cannot metabolize It cannot reproduce  Does not have the metabolic machinery nor cellular structures to do so  Once in the presence of a living cell a virus behaves as if it were alive  It reproduces by taking over the metabolic machinery of the host cell  Uses the cell’s enzymes, ribosomes, and other components

 Are viruses alive?

 Viroid: Small & Circular in shape Infectious molecule of RNA Causes many plant diseases  Prion An infectious agent Composed only of protein

 Cellular organisms  2 Domains– Bacteria & Archea  3 main shapes Cocci – Spherical  Groups of 2 – Diplococci  Long Chains – Streptococci  Irregular grape-like clumps – staphylococci Bacilli – Rod Shaped Spirilla – Helix Shaped

Fig. 19-5a, p. 370

Fig. 19-5b, p. 370

Fig. 19-5c, p. 370

 Prokaryotic cell structure is simpler than eukaryotic cell structure  Lack membrane-bound organelles No nuclei No mitochondria No chloroplasts No endoplasmic reticulum No Golgi apparatus  Mostly Unicellular  Small is size (typically 1/1000 the size of a Eukaryotic cell)  Usually have a cell wall

Fig. 19-6, p. 371

 Prokaryotes are heterotrophs Hetero = “other” Tropho = “nourishment” Must obtain organic molecules from other organism  Most are decomposers  They get their nourishment from dead organic matter  Or they live in or on other organisms  Commensals – neither help nor harm their hosts  Parasites – live at the expense of their host and can cause disease  Mutualistic – both organisms benefit from the association

 What is the difference between parasitic, commensal, and mutualistic prokaryotes?

 Some prokaryotes are Autotrophs  “Auto” = self “tropho” = nourishment  Manufacture their own organic molecules from carbon dioxide  Photosynthetic prokaryotes – Obtain energy from light  Chemiosynthetic prokaryotes - Obtain energy from chemical reactions

 Most Prokaryotes are Aerobes They require atmospheric oxygen for cellular respiration  Some are Faculative Anaerobes They use oxygen for cellular respiration if available, but will respire anaerobically when oxygen is absent  Some are Obligate Anaerobes Carry on cellular respiration only in the absence of oxygen

 Binary Fission One cell divides into two similar cells  Conjugation Two cells of different physiological mating types come together, and genetic material is transferred through pilli from one cell (donor) to the other (recipient)

Recipient cell Conjugation pilus Donor cell Fig , p. 373

 Biofilms are microbial communities that consist of many species of prokaryotes In watery environments, unicellular organisms secrete a slimy, glue-like substance rich in polysaccharides  They embed themselves in it.  Ex. Dental Plaque

ARCHAEABACTERIA  Absence of peptidoglycan in cell wall  Most live in harsh environments  Present almost universally  Abundant in air, soil, water  Abundant in bodies of organisms  FEW PLACES ON EARTH ARE COMPLETELY DEVOID OF BACTERIA

 3 Main Types Methanogens (methane producers)  Obligated anaerobes that produce methane gas from simple carbon compounds  Live in sewage and swamp sediments  Common in digestive tracts of humans and other animals Halophiles  Live in very salty environments  Use aerobic respiration to make ATP  Carry out a form of photosynthesis – using purple pigment Thermophiles  Grow in hot and acidic environments  Found in hot springs and volcanic areas under the sea

 Wall-less Bacteria Mycoplasmas A tiny bacterium bounded by a plasma membrane but lacking a typical bacterial cell wall Live in soil, sewage, or are parasitic on plants or animals  Gram-Negative Bacteria that does not retain Gram stain/do not have peptidoglycan  Gram-Positive Bacteria that do retain Gram stain/contain peptidoglycan

Table 19-1, p. 376

Fig , p. 375