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Transcript
PROKARYOTES Professor Andrea Garrison Biology 3A Illustrations ©2014 Cengage Learning unless otherwise noted Prokaryotes • Domains Bacteria and Archaea • Smallest organisms • Ubiquitous – Food source for many organisms – Decomposers – Pathogens • Commercially important – Cheeses, sour cream, biotechnology Prokaryotes 2 Prokaryotes • Very diverse domains – Diversity caused by rapid natural selection – Genetic variability is high • Higher population sizes than eukaryotes • Reproduce rapidly – Many generations, greater chance for mutations • Horizontal gene transfer – Movement of genetic material by means other than descent (binary fission) Prokaryotes 3 Prokaryote Shape • Three basic shapes Prokaryotes 4 Prokaryote Cell Structure • Cell membranes – Similar to eukaryotic cell membrane • Cytoskeleton present – Shape, cell division, directionality • No organelles – Reactions occur in cytoplasm or on cell membrane Prokaryotes 5 Prokaryote Cell Structure • Nucleoid – Central area of cell with single, circular DNA molecule • DNARNAproteins in same region (no nuclear membrane to navigate) – Ribosomes for protein synthesis Prokaryotes 6 Nucleoid Cell wall Plasma membrane Cytoplasm Ribosomes Bacterial flagellum Pili Plasma membrane Prokaryotes Cell wall Cytoplasm Nucleoid Capsule 7 Figure 5-7 p95 Prokaryote Cell Structure • Prokaryotic chromosome in nucleoid • Plasmids free in cytoplasm – Smaller circle of DNA – Gene functions supplement those of prokaryotic chromosome Prokaryotes 8 Prokaryote Cell Structure • Storage granules – Clumps of glycogen, lipids, phosphates, etc • Non-organelle structures provide appearance of “organelles” inside cytoplasm, but are not membrane-bound Prokaryotes 9 Prokaryote Cell Structure • Cell wall – Outside cell membrane • Protects cell – Bacteria cell wall made of peptidoglycan • Polysaccharide backbone tied together by polypeptides • May be slime coat of polysaccharides outside wall – Protects against damage, desiccation; helps attach to surface – If layer is loosely associated with cell = slime layer – If layer is gelatinous and firmly attached to cell = capsule – Archaeal cell walls vary in molecular structure Prokaryotes 10 Gram-positive vs Gram-negative • Staining method to distinguish different bacteria – 2-step process • Crystal violet stain, then 2nd stain – Gram-positive bacteria have thick cell wall • holds the crystal violet stain; appear purple – Gram-negative bacteria have thinner cell wall surrounded by 2nd layer of cell membrane • Doesn’t hold crystal violet stain; appear pink Prokaryotes 11 Gram-Negative Bacterium Note outer membrane Prokaryotes 12 Gram-Positive vs. Gram-Negative Prokaryotes 13 Gram-positive vs Gram-negative • Most pathogenic bacteria Gram-negative – Outer membrane protects them from body’s immune system and also antibiotics • Gram-positive bacteria more susceptible to antibiotics Prokaryotes 14 Capsulated bacteria • Capsule may be found in Gram-positive or Gram-negative bacteria • Capsule protective • Capsulated bacteria more likely to be virulent (=infectious) • Forms of same species without capsule nonvirulent Prokaryotes 15 Archaeal Cell Membranes and Walls • Archaea are extremophiles • live in extreme conditions; high heat, salt, etc. • Cell membranes made of phospholipid • Unique bonding of molecules maintain structure w/ extreme conditions • Cell walls very resistant to physical damage • Gram-negative or Gram-positive Prokaryotes 16 Prokaryotes • Flagella in some – Used for locomotion – Protein fiber rotates in socket – Structure different in Archaea Prokaryotes 17 Prokaryotes • Pili in some – Extend from cell wall – Mostly Gram-negative bacteria – Sex pili allow conjugation – Others allow bacteria to adhere to animal cells Prokaryotes 18 Horizontal Gene Transfer Increases Genetic Diversity • Conjugation – Plasmid replicated and transferred to another bacterium – Bacteria use sex pilus to touch another bacterium and form cytoplasmic bridge for conjugation Prokaryotes 19 Horizontal Gene Transfer Increases Genetic Diversity • Conjugation – Plasmid • Takes pieces of main chromosome with it during conjugation • Integrates into circular chromosome of recipient • Recombinant DNA Prokaryotes 20 Horizontal Gene Transfer Increases Genetic Diversity • Transformation – Bacteria pick up bits of bacterial DNA from environment • If dead cells were a pathogenic strain, the DNA for that trait is given to host cell (recombinant DNA) Prokaryotes 21 Horizontal Gene Transfer Increases Genetic Diversity • Transduction – Bacteriophages (viruses) produced in one bacterial cell may pick up host DNA in the bacteriophage genome • DNA from one bacteria then transferred to another bacterium when it’s infected with phage • If phage doesn’t kill bacteria, now have recombinant DNA in bacteria Prokaryotes 22 Prokaryote Metabolism • Diversity of metabolic mechanisms – All organisms take in carbon and energy • Prokaryotes show greatest diversity of mechanisms – Method of obtaining carbon • Autotrophs get carbon from atmospheric CO2 • Heterotrophs get carbon from organic molecules in other organisms – Method of obtaining energy • Chemotrophs get energy from oxidizing other molecules • Phototrophs get energy from light Prokaryotes 23 Prokaryote Metabolism Prokaryotes 24 Prokaryote Metabolism • Use of O2 to make ATP – Aerobes require O2 (ex: humans) • Obligate aerobes die without O2 – Anaerobes do not require O2 (ex: fermenting bacteria) • Obligate anaerobes die in presence of O2 – Facultative anaerobes do both (ex: yeast) • Always use O2 when present Prokaryotes 25 Prokaryote Metabolism • Nitrogen fixation – All organisms need nitrogen for amino acids and nucleic acids – N2 available in atmosphere, but unusable – Prokaryotes in soil and water convert N2 to useable form • Nitrogen fixation: N2 to ammonia – Converts immediately to ammonium – Ammonium usable by some prokaryotes • Nitrification occurs after nitrogen fixation: ammonium to nitrite then nitrite to nitrate, – 2 steps; requires 2 types of bacteria – Nitrate useable by many prokaryotes, plants Prokaryotes 26 Prokaryote Reproduction • Binary fission – Parent divides into 2 genetically identical daughter cells – Conjugation occurs in some • May result in “sexual” recombination of DNA – Endospores form in some • Created when environment unfavorable • Dormant until environment favorable (maybe thousands of years) – Water entering cells, activates metabolism Prokaryotes 27 Multicellular Associations • In nature, bacteria typically grow in mixed populations – One or more bacterial, archaeal and/or eukaryotic species • Unicellular, but act as multicellular group – May even undergo differentiation with division of labor Prokaryotes 28 Multicellular Associations • Ex: Cyanobacteria – May live singularly or form associations – Anabaena forms unicellular associations with division of labor • Heterocysts fix nitrogen • Vegetative cells photosynthesize • Spore can form dormant stage when environment unfavorable Prokaryotes 29 Multicellular Associations Prokaryotes 30 Multicellular Associations • Biofilms – Associations of one or more microorganisms • Cells secrete – signaling molecules to attract nearby cells – proteins that help the cells attach to substrate and to each other – chains of polysaccharides that trap other microorganisms and form 3-D structure • Channels form to bring nutrients to center of film and wastes to the outside – Cause tooth decay, damage to industrial and medical equipment Prokaryotes 31 Domain Bacteria • Several groups (“kingdoms”) – Only one group is Gram-positive • Chemoheterotrophs • Many cause disease (ex: Staphylococcus aureus) – Lab: phylum Cyanobacteria • photoautotrophs Prokaryotes 32 Antibiotic Resistance – Antibiotics kill bacteria – In presence of antibiotics, mutations will result in a few resistant bacteria – Some bacteria contain R plasmids that carry antibiotic resistance • R plasmids often have genes to encode sex pili – Can transfer antibiotic resistance – Often result in bacteria resistance to multiple drugs (MDR) Prokaryotes 33 Domain Archaea • First found in extreme environments – Hot springs, geysers, undersea hydrothermal vents – Later found in more normal environments • Chemoautotrophs or chemoheterotrophs • 5 branches (“kingdoms”) Prokaryotes 34
