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Transcript
Eukaryote Classification • Old 5 Kingdom system Prokaryote • Monera, Protists, Plants, Fungi, Animals • New 3 Domain system – reflects a greater understanding of evolution & molecular evidence • Prokaryote: Bacteria • Prokaryote: Archaebacteria • Eukaryotes – Protists – Plants – Fungi – Animals Archaebacteria & Bacteria Prokaryotes Domains Eubacteria and Archaebacteria Prokaryotic Cell Structure bac vid Bacteria (Eubacteria) -Prokaryotes -unicellular -most heterotrophs; some photosynthetic (cyano) -can be aerobic or anaerobic *obligate or facultative Fig. 27-2 1 µm (a) Spherical (cocci) 2 µm (b) Rod-shaped (bacilli) 5 µm (c) Spiral Structure and Function • 3 basic shapes: spherical (cocci), rods (bacillus) and spiral • Cell Wall – Peptidoglycan covers cell, anchors attachments – Archaea have no (or little) peptidoglycan Gram Staining Gram + : simple walls, lots of Peptiodoglycan (take on stain- purple color) Gram - : complex walls with lipopolysaccharides less PTG (don’t take on stain due to lipids) – Medical significance: Gram – lipids are toxic causing fever or shock and are resistant to our defenses – Gram – : antibiotic resistance (hard for drugs to penetrate) – Antibiotics often target peptidoglycan Gram Stain Benefits • Antibiotics, like penicillin break down peptidoglycans so they are affective against gram positive bacteria. • Gram negative bacteria are extremely harmful because their LPS layer is toxic. They cause fever and even shock. Strong antibiotics and alternative medicines are needed to kill them. Prokaryote Cell Wall Structure Gram-positive bacteria peptide side chains cell wall peptidoglycan plasma membrane protein peptidoglycan = polysaccharides + amino acid chains lipopolysaccharides = lipids + polysaccharides Gram-negative bacteria cell wall outer membrane of lipopolysaccharides outer membrane peptidoglycan plasma membrane Fig. 27-4 200 nm Capsule Capsule vs Fimbriae • Sticky and covers entire cell • Protection from dehydration and shield from immune system • Hair like appendages that stick • Ex. Neisseria gonorrhoeae sticks to mucus membranes • Shorter and more numerous than sex pilli Fig. 27-5 Fimbriae 200 nm Motility for most bacteria • propel themselves by flagella that are structurally and functionally different from eukaryotic flagella • PROK flagella are 1/10 the width of EUK • PROK flagella are not covered by plasma mem Motility • Different composition and propulsion • The motor of the flagella is the basal apparatus (rings embedded in the cell wall) • ATP proton pump generates power by turning hook attached • Hook is attached to chains of flagellin • In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli Video: Prokaryotic Flagella (Salmonella typhimurium) Fig. 27-6 Flagellum Filament 50 nm Cell wall Hook Basal apparatus Plasma membrane Fig. 27-8 Chromosome Plasmids 1 µm mitochondria Variations in Cell Interior cyanobacterium (photosythetic) bacterium chloroplast aerobic bacterium Reproduction and Adaptation • Binary fission in optimal conditions as often as every 20 min • They are small and have short generation time • Endospores (ability to endure hardship) Endospores -endospores- a tough covering containing bacteria DNA. -produced in unfavorable environments -bacteria will lie dormant until conditions are right (years) -extreme heat and acidic cleaners must be used to sterilize surfaces containing endospores -can cause- botulism in unsterilized canned foods, or tetanus in wounds What you need to know: • Mechanisms that contribute to genetic diversity in prokaryotes, including transformation, conjugation, transduction, and mutation. Rapid Evolution: high genetic diversity • 2 strains of E.coli differ in an rRNA gene more than between a human and a platypus • Rapid reproduction • Mutation • Genetic recombination Mutation • Probability of a spontaneous mutation in an E.coli gene is 1 in 10 million/division • 2x1010 new E.coli per day • About 2000 bacteria will have mutations • 4300 genes total in E.coli • 4300 x 2000 = 9 million mutation per day in the human intestines • Don’t memorize specific data! Just a FYI Genetic Recombination • Transformation: uptake foreign DNA – Ex. Competent cells, pneumonia • Transduction: a bacteriophage performs horizontal gene transfer • Conjugation- bacterial “sex” • Plasmids often used for transformation Fig. 27-11-4 Phage DNA A+ B+ Transduction A+ B+ Donor cell A+ Recombination A+ A– B– Recipient cell A+ B– Recombinant cell Conjugation and Plasmids • Conjugation is the process where genetic material is transferred between bacterial cells • Sex pili allow cells to connect and pull together for DNA transfer • A piece of DNA called the F factor is required for the production of sex pili • The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome Fig. 27-12 Sex pilus 1 µm The F Factor as a Plasmid • Cells containing the F plasmid function as DNA donors during conjugation • Cells without the F factor function as DNA recipients during conjugation • The F factor is transferable during conjugation (recipient can become donor) Fig. 27-13 F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Hfr cell A+ A+ A+ F factor F– cell A+ A– Recombinant F– bacterium A– A– (b) Conjugation and transfer of part of an Hfr bacterial chromosome A+ A– A+ R Plasmids and Antibiotic Resistance • R plasmids carry genes for antibiotic resistance • Antibiotics select for bacteria with genes that aren’t resistant to the antibiotics • Antibiotic resistant strains of bacteria are becoming more common Bacterial Diversity -Diverse nutritional modes -Role of oxygen in metabolism -Nitrogen metabolism nitrogen fixation: converting N2 from the atmosphere into nitrates or ammonia (NH3) Table 27-1 Fig. 27-14 Photosynthetic cells Heterocyte 20 µm Heterocyte A heterocyte (or heterocyst, in older terminology) is a specialized thick-walled cell that is dedicated to fixing atmospheric nitrogen in certain cyanobacteria. These cells do not photosynthesize, since the enzyme that carries out nitrogen fixation is inhibited by oxygen. Prokaryotic phylogeny Eukarya Archaea Bacteria Eukarya Bacteria Archaea • Archaea more closely related to eukaryotes than bacteria • polyphyletic Fig. 27-16 Euryarchaeotes Crenarchaeotes UNIVERSAL ANCESTOR Nanoarchaeotes Domain Archaea Korarcheotes Domain Eukarya Eukaryotes Proteobacteria Do not have to know the specific names! Just the trend Spirochetes Cyanobacteria Gram-positive bacteria Domain Bacteria Chlamydias Table 27-2 Proteobacteria- *don’t have to know the name • These gram-negative bacteria include photoautotrophs, chemoautotrophs, and heterotrophs • Some are anaerobic, and others aerobic -*Facultative anaerobes vs obligate anaerobes. What’s the difference? Fig. 27-18a Subgroup: Alpha Proteobacteria Alpha Beta Gamma Proteobacteria 2.5 µm Delta Epsilon Rhizobium (arrows) inside a root cell of a legume (TEM) Subgroup: Beta Proteobacteria 0.5 µm 1 µm Subgroup: Gamma Proteobacteria Thiomargarita namibiensis containing sulfur wastes (LM) Nitrosomonas (colorized TEM) Subgroup: Delta Proteobacteria Subgroup: Epsilon Proteobacteria Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Bdellovibrio bacteriophorus attacking a larger bacterium (colorized TEM) 2 µm 5 µm 10 µm B. bacteriophorus Helicobacter pylori (colorized TEM) Subgroup: Alpha Proteobacteria (*don’t have to know name) • Many species are closely associated with eukaryotic hosts • Scientists hypothesize that mitochondria evolved from aerobic alpha proteobacteria through endosymbiosis • Example: Rhizobium, which forms root nodules in legumes and fixes atmospheric N2 • Arrows in the next slide are Rhizobium • Example: Agrobacterium, which produces tumors in plants and is used in genetic engineering 2.5 µm Fig. 27-18c Rhizobium (arrows) inside a root cell of a legume (TEM) Cyanobacteria • These are photoautotrophs that generate O2 • Plant chloroplasts likely evolved from cyanobacteria by the process of endosymbiosis Two species of Oscillatoria, filamentous cyanobacteria (LM) Concept 27.6: Prokaryotes have both harmful and beneficial impacts on humans • Some prokaryotes are human pathogens, but others have positive interactions with humans • Bacteria are important recyclers; N2 fixation, etc • Prokaryotes cause about half of all human diseases • Lyme disease is an example Fig. 27-21 5 µm • Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins • Exotoxins cause disease once the toxin is released, even if the prokaryotes that produce them are no longer present. Ex- Botulism, cholera • Endotoxins (gram – and in outer membrane) are released only when bacteria die and their cell walls break down. Ex- Salmonella. *Gram – have lipopolysaccharide • Many pathogenic bacteria are potential weapons of bioterrorism Archaea • Archaea share certain traits with bacteria and other traits with eukaryotes • DNA and amino acid sequencing have shown that Archaea are more related (i.e, more recent common ancestor) to D. Eukarya than to D. Eubacteria (see table 27.2, shown earlier in this presentation) Characteristics of Bacteria DOMAIN Bacteria CHARACTERISTICS -Nuclear envelope absent -Membrane enclosed organelles absent -Peptidoglycan in cell walls -Unbranched hydrocarbons in membrane lipids -1 kind of RNA polymerase -Formylmethionine for initiator of amino acids in protein synthesis -Introns rare -Antibiotics inhibit growth -Circular chromosome EXAMPLE Alpha Beta Gamma Delta Epsilon Chlamydias Spirochetes Cyanobacteria Gram-positive bacteria (*don’t have to know these!) Characteristics Of Archaea Archaea •Nuclear envelope absent •Membrane enclosed organelles absent •Some branched hydrocarbons in membrane lipids •Several kinds of RNA polymerase •Methionine initiator amino acid for protein synthesis •Introns present in some genes •Antibiotics do not inhibit growth •Have histones & circular chromosome Korarchaeotes Euryarchaeotes Crenarchaeotes Nanoarchaeotes *Don’t have to know these! Characteristics of Eukarya Eukarya -Nuclear envelope present -Membrane bound organelles -Unbranched hydrocarbons in membrane lipids -Several kinds of RNA polymerase -Methionine initiator amino acid for protein synthesis -Antibiotics do not inhibit growth -Histones present Eukaryotes (plants, animals, protists, fungi) Most archaea live in extreme environments • Extreme thermophiles thrive in very hot environments • Extreme halophiles live in high saline environments • Some use CO2 (not O2) to oxidize H2 and produce methane as waste- Methanogens. Exswamps (“bubbles” are methane- CH4) (*Aerobic organisms use O2 for oxidation. Remember Cellular Respiration!) Ecological Importance of Prokaryotes • Decomposers – Convert inorganic compounds into forms that can be taken up by other organisms • Nitrogen fixation – – Prokaryotes can metabolize nitrogen in a variety of ways; In nitrogen fixation, some prokaryotes convert atmospheric nitrogen to ammonia • Oxygen production (if autotrophic) • Symbiotic relationship with eukaryotes (*ex- your digestion: remember Lac and Trp operons in prokaryotes) • Prokaryotes are so important to the biosphere that if they were to disappear, the prospects for any other life surviving would be bleak….
