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Prokaryotes – aka Bacteria
– Prokaryotes• are found wherever there is life,• have a collective biomass that is at least ten times
that of all eukaryotes,• thrive in habitats too cold, too hot, too salty, too
acidic, or too alkaline for any eukaryote,• cause about half of all human diseases, and• are more commonly benign or beneficial.
The Structure and Function of Prokaryotes
– Prokaryotic cells• lack a membrane-enclosed nucleus,• lack other membrane-enclosed organelles,• typically have cell walls exterior to their plasma
membranes, but• display an enormous range of diversity.
The Structure of Prokaryotes
Plasma membrane
Cell wall
Capsule
Prokaryoticflagellum
Ribosomes
Nucleoid
Pili
Identifying Prokaryotes
• * Prokaryotes are identified by:– Their shapes– The chemical natures of their cell walls– The ways they move
Cell Shape
• Three shapes possible:• Rod shaped – called bacilli
• Sphere-shaped – called cocci
• Spiral-shaped – called spirilla
• Can form chains or clumps/clusters – use these prefixes:
• Diplo = pair• Strepto = chain• Staphlyo = cluster/bunch
– Ex. Diplobacilli = pair of rod-shaped bacteria– Ex. Streptococci = chain of sphere-shaped bacteria– Ex. Staphlyococci = cluster/bunch of sphere-shaped bacteria
Cell Wall
• Gram staining – 2 stains: 1 violet, 1 red – Bacteria stain purple – Gram positive – cell
wall contains mainly peptidoglycan– Bacteria stain red – Gram negative – have
second, outer, layer of lipid and carbohydrate molecules
Bacterial Movement
– Flagella – whip-like structures for movement– Slime-like material like a slug– May not move at all
Growth and Reproduction
• Can divide every 20 minutes!• Growth held in check by food and waste
products (think limiting factors)• Binary fission – just like cell division – two
“daughter” cells – asexual reproduction• Conjugation – transfer genetic material from one
cell to another – increases genetic diversity• Spore formation – form endospores when
conditions are unfavorable for growth
Obtaining Energy
• Autotrophs– Photoautotrophs – found where light is plentiful
(surfaces of lakes, streams, oceans)– Chemoautotrophs – energy from inorganic molecules
– chemical reactions (hydrothermal vents on ocean floor)
• Heterotrophs – Most bacteria are heterotrophs, like humans – may
even compete with humans for food – can lead to food poisoning
– Photoheterotrophs – combine autotrophic and heterotrophic styles
Releasing Energy
• Respiration – requires oxygen (O2) – obligate aerobes
• Fermentation – absence of oxygen (O2) – obligate anaerobes
• Facultative Anaerobes – can live with or without oxygen (O2) – can switch between respiration and fermentation = grow just about anywhere
The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea
• 2 Kingdoms – used to be just be one - Monerans - By comparing diverse prokaryotes at the molecular level, biologists have identified two major branches of prokaryotic evolution:
– Bacteria – larger of two kingdoms; live almost everywhere, E. coli, cell walls contain peptidoglycan
– Archaebacteria – cell walls lack peptidoglycan, may be ancestors of eukaryotes, live in extremely harsh environments (oxygen-free, salty, hot)
Bacteria and Disease
– Bacteria and other organisms that cause disease are called pathogens.
– Most pathogenic bacteria produce poisons.
****Disease – some bacteria damage the tissues of the infected organism directly by breaking them down for food. Others release toxins (poisons) that harm the body.****
• Vaccines can prevent bacterial infections (ex. tetanus shots). Antibiotics block growth and reproduction of bacteria; cure many bacterial diseases; sanitation important
Common Diseases Caused by Bacteria
Tooth decay
Lyme disease
Tetanus
Tuberculosis
Salmonella food poisoning
Pneumonia
Cholera
Streptococcus mutans
Borrelia burgdorferi
Clostridium tetani
Mycobacterium tuberculosis
Salmonella enteritidis
Streptococcus pneumoniae
Vibrio cholerae
Regular dental hygiene
Protection from tick bites
Current tetanus vaccination
Vaccination
Proper food-handling practices
Maintaining good health
Clean water supplies
Disease Pathogen Prevention
Bacteria in Nature
– Pathogenic bacteria are in the minority among prokaryotes.
– Far more common are species that are essential to our well-being, either directly or indirectly.
– * Bacteria are vital to maintaining the living world. Some are producers that capture energy by photosynthesis. Others help to break down the nutrients in dead matter and the atmosphere, allowing other organisms to use the nutrients.
Bacteria in the Environment - Benefits
• Decomposers – nutrient/chemical recycling (dead trees, leaves, etc.)• Nitrogen fixation – convert pure nitrogen (N) to compounds that can be used
by other organisms– Ex. Clover plants and nodules on roots with bacteria inside
• Symbiotic relationships with other organisms– Us – E. coli and our intestines– Cattle – bacteria to help them digest cellulose
Human Uses of Bacteria
• Food – cheese, yogurt, buttermilk, sour cream, pickles, vinegar, some bread
• Industry – Bioremediation - digest oil spills, remove waste products/poisons in the water, sewer treatments, synthesize drugs and chemicals