Prokaryotes PDF

1 Chapter 17.3 The Prokaryotes 2 Prokaryotes are single-celled organisms that make up domains Bacteria and Archaea Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 µm (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Bacillus coagulans (TEM) ku....

1 Chapter 17.3 The Prokaryotes 2 Prokaryotes are single-celled organisms that make up domains Bacteria and Archaea Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 µm (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Bacillus coagulans (TEM) ku.ac.ae Adapted to diverse and extreme environments, they are the most abundant organisms on Earth Halophiles—require high salt concentrations to grow Thermoacidophiles—extremely hot, acidic environments like hot springs and submarine thermal vents (80°C ) Why is this lake’s water pink? ku.ac.ae Archaea in the genus Halobacterium 5 The Prokaryotes The prokaryotic genome has less DNA than the eukaryotic genome Most of the genome consists of a circular chromosome No nucleus—single circular chromosome found in nucleoid (region of cell) No membrane-bounded organelles Cytoplasm surrounded by plasma membrane and cell wall Sometimes a capsule—protective layer Cell wall maintains the shape of a cell Far greater metabolic capabilities than more complex organisms Structural and functional adaptations contribute to prokaryotic success 6 Prokaryotic Cell Structure Access the text alternative for slide images. 7 Origin of the First Cells First living cells were prokaryotes. Found in rocks 3.5 billion years old May have existed before that but no fossils found yet Conditions on early Earth very different from today. Temperatures high, little free oxygen Abiotic (without life) synthesis of organic molecules with input from energy sources Lightning, sunlight, meteorite impact, volcanic activity 8 Origin of the First Cells Protocells Cell-like structures complete with outer membrane. May have resulted from self-assembly of macromolecules Gave rise to cellular life Some researchers think the first hereditary molecule was RNA. Over time, the more stable DNA became the long-term solution. 9 Bacteria Most diverse and prevalent organisms on Earth Tens of thousands of different bacteria identified Likely many more exist but not yet identified What are the 5 criterion to identify a bacteria ? 1. 2. 3. 4. 5. Shape Membrane Type Oxygen Needs Energy and Carbon Sources Nitrogen Metabolism 1. Shape Some form chains or bunches. Most are unicellular, but some species form colonies Most common three shapes—rods (bacilli), spheres (cocci), and spirals (spirilla or spirochetes) Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells Plasmids—extrachromosomal DNA in some Bacteria have ribosomes but no membrane-bounded organelles. Motile bacteria generally have flagella but never cilia—not like eukaryotic flagella. 1. Shape 2. Membrane Type (Gram-Staining) Outer cell wall is strengthened by peptidoglycan. Prevents bursting or collapsing Some have additional capsule outside the cell wall Note: Archea don’t have peptidoglycan 2. Membrane Type (Gram-Staining) Eukaryote cell walls are made of cellulose or chitin Most bacterial cell walls instead contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides Archaeal walls contain a variety of polysaccharides and proteins, but lack peptidoglycan 2. Membrane Type (Gram-Staining) Scientists use the Gram stain to classify bacteria by cell wall composition Gram-positive bacteria have simpler walls with a large amount of peptidoglycan The walls of gram-negative bacteria have less peptidoglycan and are more complex with an outer membrane that contains lipopolysaccharides 2. Membrane Type (Gram-Staining) Gram-positive bacteria include Gram-Positive Bacteria Actinomycetes, which decompose soil Bacillus anthracis, the cause of anthrax Clostridium botulinum, the cause of botulism Some Staphylococcus and Streptococcus, which can be pathogenic – Mycoplasms, the smallest known cells 5 µm – – – – Streptomyces, the source of many antibiotics (SEM) 3. Oxygen Needs Obligate aerobes : must use oxygen Obligate anaerobe: are poisoned by oxygen, uses fermentation or anaerobic respiration Facultative anaerobe: uses oxygen when available and fermentation or anaerobic respiration if not 4-Bacterial Nutrition Autotrophs require CO2 as a carbon source (e.g. plants) Heterotrophs require an organic nutrient to make organic compounds (e.g. animals) Phototrophs obtain energy from light (plants) Chemotrophs obtain energy from chemicals 19 4- Bacterial Nutrition (autotrophs) Photoautotrophs (Like plants) Cyanobacteria (Photosynthetic bacteria) Use solar energy and carbon dioxide to make food Chemoautotrophs Don’t use solar energy to reduce carbon dioxide Like deep sea vent bacteria living inside tube worms Chemoheterotrophs (Like animals) Most bacteria are chemoheterotrophs Take in organic molecules as a source of energy and carbon 5. Nitrogen Metabolism Nitrogen is essential for the production of amino acids and nucleic acids in all organisms Nitrogen fixation Plants are unable to fix atmospheric nitrogen (N₂ gas). Bacteria converts N₂ into a form that plants use ammonia (NH3) N2 N2 ATMOSPHERE SOIL Nitrogen-fixing bacteria Denitrifying bacteria H+ (from soil) NH3 NH4+ Ammonifying (ammonia) (ammonium) bacteria Organic material (humus) Nitrate and nitrogenous organic compounds exported in xylem to shoot system NH4+ Nitrifying bacteria NO3(nitrate) Root 21 Nitrogen fixation: Nodules of a Legume Mutualistic bacteria live inside root nodules. Appendeges in prokayotes: Fimbriae Stick to substrates Flagellum Motility Flagella—propulsion Fimbriae—attachment to surfaces Conjugation pili—DNA transfer Pilus To exchange DNA Internal Organization and DNA 1 µm 0.2 µm Lack of complex compartmentalization but specialized membranes (metabolic functions) Respiratory membrane Circular chromosome (nucleoid) Sometimes some small DNA molecules called plasmids DNA replication, transcription and Translation similar to eukaryotes (smaller ribosomes, protein complex involved …) Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote Chromosome Plasmids 1 µm Endospores Bacteria can produce a “sleeping” structure able to survive to harsh conditions Dehydrate and collapse inside three heavy spore coats Can survive harshest environments Survive for very long periods of time Coat Endospore 0.3 µm 25 Bacteria Reproduce Asexually Bacteria (and archaea) reproduce asexually by binary fission. Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes Key features of prokaryotic reproduction: 1. They are small 2. They reproduce by binary fission (every 1–3 hours) 3. They have short generation times https://simple.wikipedia.org/wiki/Binary_fission Genetic recombination Genetic diversity is due to Genetic recombination through three processes. Transformation: taking up and incorporating foreign DNA from the surrounding environment. Transduction: the movement of genes between bacteria by phages (from “bacteriophages,” viruses that infect bacteria) Conjugation: the process where genetic material is transferred between prokaryotic cells Genetic recombination Transformation Transduction Conjugation Phage 1 µm A+ B+ Donor cell Sex pilus A+ B+ A+ Recombination A+ A- B- A+ B- Recipient cell Recombinant cell 29 Prokaryotes play crucial roles in the biosphere Why prokaryotes are important ? Primary producers (base of food chain) Frees oxygen from carbon dioxide Chemoheterotrophic prokaryotes function as decomposers, digest dead organic remains to return inorganic nutrients to producers. Life would halt without decomposers Prokaryotes can increase the availability of nitrogen, phosphorus, and potassium for plant growth Prokaryotes are the principal agents in bioremediation, the use of organisms to remove pollutants from the environment Ecological interactions of Prokaryotes Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont - Mutualism, both symbiotic organisms benefit - Commensalism, one organism benefits while neither harming nor helping the other in any significant way - Parasitism, an organism called a parasite harms but does not kill its host Parasites that cause disease are called pathogens Prokaryotes have both beneficial and harmful impacts on humans Some prokaryotes are human pathogens, but many others have positive interactions with humans Beneficial bacteria Bacteria that break down food that is undigested by our intestines Pathogenic bacteria Bacteria cause about half of all human diseases e.g more than 1.5 million people die each year of tuberculosis (Mycobacterium tuberculosis) Salmonella Cholera … Bacteria in Food Science and Biotechnology Wide variety of foods use bacteria. Fermentation produces lactic acid. Pickles cucumbers, curdles milk into cheese, and gives tangy flavor Experiments using prokaryotes have led to important advances in DNA technology For example, E. coli is used in gene (to produce vitamins, antibiotics, and hormones) Insulin, human growth hormone, and vaccines Most antibiotics are discovered in soil bacteria. 34 Applications using bacteria Bacteria can also be used in bioremediation, the use of organisms to remove pollutants from the environment Ability of bacteria to break down pollutants is exploited Some bioengineered Damage from human impact can be lessened if conditions are right (nutrients, such as nitrogen and phosphates). (example Deep Water Horizon spill). 35 Bacterial Diseases in Humans Pathogens are able to produce a toxin and/or adhere to surfaces and sometimes invade organs or cells. Toxins are small organic molecules or pieces of bacteria released when bacteria die. Often, toxins cause more problems than the growth of the microbe itself. Clostridium tetani causes tetanus (lock jaw). Antibiotics generally either inhibit protein synthesis or inhibit cell wall production. Thank You ku.ac.ae