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Lab 17 on Thursday Prokaryotes and Viruses Chapter 25 Learning Objectives • Describe prions and the diseases they cause • Describe general characteristics of Prokaryotes • Compare and contrast bacteria, archeae and eukarya • Compare and contrast gram positive and gram negative bacteria • Describe gram + and gram- bacteria • Describe the three main bacterial shapes Why It Matters • Prokaryotes: The smallest organisms Prions • Infectious proteins with no associated nucleic acids • Misfolded versions of normal cellular proteins that can induce other normal proteins to misfold Prion Diseases Degenerate nervous system in mammals – Scrapie: Brain disease in sheep – Mad cow disease (Bovine spongiform encephalopathy): Spongy holes and protein deposits in brain tissue – Creutzfeldt-Jakob disease: Rapid mental deterioration, loss of vision and speech, paralysis – Kuru-cannibalistic tribe in New Guinea, Brain Tissue Damaged by BSE 25.1 Prokaryotic Structure and Function • Prokaryotes are simple in structure compared with eukaryotic cells • Prokaryotes have the greatest metabolic diversity of all living organisms • Prokaryotes differ in whether oxygen can be used in their metabolism 25.1 (cont.) • Prokaryotes fix and metabolize nitrogen • Prokaryotes reproduce asexually or, rarely, by a form of sexual reproduction • In nature, bacteria may live in communities attached to a surface Prokaryotes • Colonize a great diversity of habitats • Are small but complex cells • Have great metabolic diversity • Adapt rapidly to their environments Three Common Shapes in Prokaryotes • Spherical: cocci • Rodlike: bacilli • Spiral: vibrios (curved) and spirilla (helix) Prokaryotic Genomes • Prokaryotic chromosome – Single, circular DNA molecule – Packaged into nucleoid • No nucleolus • No nuclear membranes • Plasmids – Small circles of DNA – Genes supplement nucleoid genes – Replicate independently (along with main DNA) Plasmid Pili Cytoplasm Folded DNA containing molecule (in the nucleoid) ribosomes Flagellum Capsule Plasma Peptidomembrane glycan layer Outer membrane Cell wall Fig. 25-3, p. 528 Prokaryotic Ribosomes • Bacterial ribosomes – Smaller than eukaryotic ribosomes – Protein synthesis similar to eukaryotes • Archaeal ribosomes – Size similar to bacteria – Different structure – Protein synthesis is combination of bacterial and eukaryotic processes Prokaryotic Cell Wall • Protects plasma membrane – Helps withstand osmotic pressure – Prevents action of detergent-like chemicals • Made of peptidoglycans – Polysaccharide polymers connected by short polypeptides Gram Stain • Gram stain technique – Stain with crystal violet, then with iodine • Fixes dye to cell wall – Wash with alcohol – Stain again with fuchsin or safranin • Gram-positive bacteria – Appear purple because crystal violet retained • Gram-negative bacteria – Appear pink because crystal violet lost Gram-Positive Bacteria • Single, relatively thick peptidoglycan layer Capsule may be present a. Gram-positive bacterial cell wall Peptidoglycan layer Plasma membrane Cell wall Cytoplasm Fig. 25-4, p. 529 Gram-Negative Bacteria • Two-layered walls; relatively thin peptidoglycan sheath surrounded by outer membrane b. Gram-negative bacterial cell wall Capsule Outer membrane Peptidoglycan layer Plasma membrane Cell wall Cytoplasm Fig. 25-4, p. 529 Slime Coat • Capsule – Slime attached to cells • Slime layer – Loosely associated with cells • Protects bacteria from desiccation, antibiotics, viruses, antibodies, and enzymes • Helps bacteria adhere to surfaces Pili • Rigid protein shafts extend from cell walls • Mostly in Gramnegative bacteria • Help bacteria attach to each other or to surfaces Obtaining Carbon and Energy (1) • Autotrophs (auto = self; troph = nourishment) – Use carbon dioxide as their carbon source • Heterotrophs – Obtain carbon from organic molecules Obtaining Carbon and Energy (2) • Chemoautotrophs – Obtain energy by oxidizing inorganic or organic substances • Phototrophs – Use light as energy source Organic molecules Carbon source CO2 Energy source Oxidation of molecules Light CHEMOAUTOTROPH PHOTOAUTOTROPH Found in some bacteria Found in some photoand archaeans; not synthetic bacteria, in found in eukaryotes some protists, and in plants CHEMOHETEROTROPH PHOTOHETEROTROPH Include some bacteria and archaeans, and also in protists, fungi, animals, and plants Found in some photosynthetic bacteria * Inorganic molecules for chemoautotrophs and organic molecules for chemoheterotrophs. Fig. 25-8, p. 531 Prokaryotes and Oxygen: Aerobes • Aerobes – Require oxygen for cellular respiration – Oxygen is the final electron acceptor • Obligate aerobes – Cannot grow without oxygen Prokaryotes and Oxygen: Anaerobes • Anaerobes – Do not require oxygen to live • Obligate anaerobes (poisoned by oxygen) – Use fermentation or type of respiration in which inorganic molecules (NO3– or SO42–) are final electron acceptors • Facultative anaerobes – Use O2 when present – Use fermentation under anaerobic conditions Prokaryotes and Nitrogen (1) • Nitrogen fixation – Conversion of atmospheric nitrogen (N3) to ammonia (NH3) – Ammonia ionized to ammonium (NH4+) for biosynthesis • Nitrogen-fixing bacteria include – Some cyanobacteria – Free-living Azotobacter – Bacteria such as Rhizobium that are symbiotic with plants Prokaryotes and Nitrogen (2) • Nitrification – Conversion of ammonium (NH4+) to nitrate (NO3–) – Two-step conversion by nitrifying bacteria • Some types of bacteria convert ammonia to nitrite (NO2–) • Other types convert nitrite to nitrate Prokaryote Reproduction • Binary fission – Asexual reproduction – Produces exact copies of parent • Conjugation – Two cells connected by pilus – Part of DNA of one cell is transferred to another cell (usually plasmids) Endospore • Develops inside some bacteria when environmental conditions are unfavorable • Metabolically inactive • Highly resistant to heat, desiccation, attack by enzymes or chemicals Endospore: Clostridium tetani 25.2 Domain Bacteria • Molecular studies reveal more than a dozen evolutionary branches in the Bacteria • Bacteria cause diseases by several mechanisms • Pathogenic bacteria commonly develop resistance to antibiotics Classification of Prokaryotes Bacteria • 12 separate evolutionary branches • Six most important groups: – Proteobacteria – Green bacteria – Cyanobacteria – Gram-positive – Spirochetes – Chlamydias The Proteobacteria (1) • Gram-negative bacteria – Purple sulfur (photoautotrophic) – Purple nonsulfur (photoheterotrophic) – Purple photosynthetic pigment • Free-living proteobacteria (chemoheterotrophs) – Some cause human diseases • Bubonic plague, Legionnaire’s disease, gonorrhea, gastroenteritis, dysentery – Some plant pathogens • Rot, scabs, wilts The Cyanobacteria • Gram-negative photoautotrophs • Blue-green color • Photosynthesis similar to plants • Release oxygen as byproduct of photosynthesis b. c. Heterocyst Resting spore Fig. 25-13, p. 535 The Gram-Positive Bacteria (1) • Primarily chemoheterotrophs • Many pathogenic species – Anthrax – Staphylococcus • Food poisoning, skin infections, toxic shock syndrome, pneumonia, meningitis – Streptococcus • Strep throat, pneumonia, scarlet fever, kidney infections The Gram-Positive Bacteria (2) • Some beneficial species – Lactobacillus • Lactic acid fermentation used to produce pickles, sauerkraut, yogurt • Mycoplasmas – Naked cells that have lost their cell walls – Smallest known cells (0.1 to 0.2 µm in diameter) The Spirochetes • Gram-negative spiral-shaped bacteria – Propelled by rotation of flagella – Enables movement in thick mud and sewage • Beneficial or harmless species – Spirochetes in termite intestine digest plant fiber – Treponema in mouth • Pathogenic species – Syphilis, relapsing fever, Lyme disease The Chlamydias • Gram-negative bacteria – Cell walls with membrane outside – Lack peptidoglycans • Intercellular parasites that cause diseases in animals Bacterial Disease Mechanisms • Exotoxins – Toxic proteins leaked or secreted • Clostridium botulinum (botulism exotoxin) • Endotoxins – Toxins only released when bacteria die or lyse • E. coli, Salmonella, Shigella • Exoenzymes – Enzymes secreted that digest plasma membrane • Streptococcus, Staphylococcus, Clostridium Resistance to Antibiotics • Pathogenic bacteria may develop resistance to antibiotics – Mutation of their own genes – Acquiring resistance genes from other bacteria • Resistant strains difficult to treat with conventional antibiotics • Resistance is a form of evolutionary adaptation 25.3 Domain Archaea • Archaea have some unique characteristics • Molecular studies reveal three evolutionary branches in the Archaea The Archaea • Archaea are more closely related to domain Eukarya than domain Bacteria • Characteristics – Some features like bacteria – Some features like eukaryotes – Some unique features Characteristics of Bacteria, Archaea, and Eukarya