Lecture'12'Prokaryotes:''''“Prokaryotes”,'oldest'and'simplest'life'form.'We'use'quotations'when'talking'about'them'because'they'do'not'constitute'an'evolutionary'linage;'they'aren’t'monophyletic.'They'are'fundamentally'different'from'eukaryotes'in'many'ways:'''Prokaryotes:'• Unicellular''§ but'some'do'form'colonies,'or'they'can'string'together'to'form'filaments'(this'makes'them'look'multicellular'but'are'not.)''• No'membraneDbound'organelles,'or'cytoskeleton.'''• No'nucleus='unDnucleated'organisms/species.''• The'enzymes'and'the'cell'protein'are'free9floating'or'in'the'cell'membrane.'''• Single9circular'DNA'chromosome'that'is'found'in'a'nucleoid'region'of'the'cell,'(where'the'nucleus'would'be'if'prokaryotes'had'one)'§ In'contrast'to'the'membrane'bound'nucleolus'in'eukaryotes,'the'genome'in'most'bacteria'is'the'single'circular'double'stranded'DNA'molecule.'This'is'the'bacterial'chromosome;'it'lacks'chromatin,'which'is'present'in'eukaryote'chromosomes.'''• Asexual'method'of'cell'replication,'called'Binary'Fission.'The'process'is'like'splitting'in'half.'§ Binary'Fission'can'be'extremely'fast.'For'example,'Ecoli'can'reproduce'every'20'minutes.'But'Some'bacteria'reproduce'a'lot'slower'like'hours'or'days.'For'example,'bacteria'living'in'the'earth’s'crust'and'take'over'a'century'to'reproduce.'This'diversity'in'generation'times'show'variability'in'prokaryotes.''• Prokaryotes'don’t'have'regular'access'to'recombination'because'they'do'not'use'meiosis'for'reproduction.'But'this'doesn’t'mean'that'genes'do'not'move'around'in'these'groups.''§ Horizontal'Transfer'of'genes'is'the'movement'of'chunks'of'DNA'of'one'prokaryote'to'another.'Extremely'common'in'prokaryotes.'Sometimes'this'crosses'specie’s'borders.'''• Thermotoga'MaritimaD'§ Bacteria'that'can'survive'at'extremely'high'temperatures.''§ When'gene'sequences'for'proteins'from'this'organism'have'been'compared'with'the'protein'sequences'from'other'species,'almost'20%'of'the'genes'in'this'bacteria'are'Archaean'in'origin.''§ This'shows'Horizontal'Gene'Transfer'between'species'from'different'domains'from'the'tree'of'life.'''• These'traits'aren’t'pasted'vertically'through'time'from'generation'to'another,'but'it'can'travel'horizontally.'Some'have'argued'that'bacteria'and'Achaea'can'be'a'web'of'life.'Some'say'that'they'are'tree'like.'Not'clear.'''• Simple'single'fibers'for'their'Flagella''• The'Cell'Wall'is'found'in'ALL'prokaryotes.'It'is'ubiquitous,'made'up'of'either'peptidoglycan'or'psuedomurein.''§ Cell'Walls'differ'between'Bacteria'and'Archaea.''♦ When'you'stain'one'of'the'cells'with'a'simple'stain'called'the'gram'stain,'the'components'of'the'cell'wall'will'become'extremely'critical.'Most'bacteria'are'gram'positive'and'gram'negative.'The'gramDpositive'cells'have'uniformly'dense'cell'walls'made'of'peptidoglycan.'The'peptidoglycan'retains'the'stain'and'dye,'which'turns'blue'or'purple.'♦ The'gram'negative'ones;'they'have'a'thin'layer'of'peptidoglycan.'It’s'surrounded'by'other'cell'wall'and'inner'plasma'membrane.'They'don’t'retain'the'stain'and'appear'red.'''♦ Since'Achaeans'don’t'have'peptidoglycan,'they'are'considered'gram'negative.'♦ The'cell'wall'is'a'target'of'antibiotics'because'eukaryotes'cells'infected'by'bacteria,'don’t'have'cell'walls'which'can'be'hurt'by'the'medicine.'This'is'how'penecillian'works'by'disrupting'the'cell'wall.''• Prokaryotes'are'very'small'in'size.''''' ' ' ' ' ' ' ' ' ' ' ''Bacteria'Classification'• Prokaryote'classification'can'be'broken'up'into'two'time'periods:'Before'DNA'analysis'and'after.''§ Pre9DNA'analysis,'we'didn’t'know'about'Achaeans.'We'only'talked'about'Bacteria.'''♦ ShapeD'we'separated'them'by'what'we'looked'liked.'The'main'way'was'shape.'Shape'divides'bacteria'into'rods'(Bacillus),'spheres'(Coccus)'and'spirals'(Spirillum).'''♦ Metabolic'StyleD'One'of'the'most'diverse'organisms'in'terms'of'metabolic'style.'Metabolism'is'how'organisms'obtain'nutrients.''DWe'divide'metabolic'styles'up'into'two'ways:'''First'way:'Ø Metabolism'by'the'response'to'oxygen.'We'call'organisms'that'need'oxygen'to'metabolize,'“Aerobes”.'Ø AnaerobicD'poisoned'by'oxygen.'Cannot'tolerate'oxygen,'which'are'called'“Obligate'Anaerobes”.''Ø Some'anaerobes'can'move'between'anaerobic'forms'of'metabolism,'like'fermentation'and'aerobic'forms'like'cellular'respiration'which'are'called'“Facultative'Anaerobes”''Ø Anaerobes'that'cannot'use'oxygen'for'metabolism'don’t'use'cellular'respiration'but'not'harmed'by'oxygen.'They'are'called'“Aerotolerant'Anaerobes”.'''Second'way:''Ø How'they'acquire'nutrients:'Autotrophs'Vs'Heterotrophs'Ø AutotrophsD'self'feeders'Ø HeterotrophsD'other'feeders''• Bacteria'have'representatives'that'show'characteristics'from'both'metabolic'styles.'One'of'the'only'groups'that'can'do'this.'''• Achaeans'can'either'be'autotrophic'or'heterotopic''• Some'bacteria'are'Photoautotrophs'o They'capture'light'to'make'energy'and'make'oxygen'as'a'byproduct'as'their'metabolism.'Critical'to'the'change'of'atmosphere'in'early'earth'(cyanobacteria).'They'use'chlorophyll'as'a'light'capturing'pigment.'Use'water'as'electron'donor'and'break'down'carbon'dioxide'to'make'sugars,'releasing'oxygen'in'the'process'(like'in'the'modern'plants).'Organisms'with'this'metabolism'form'the'base'of'most'food'chains'throughout'our'planet.'''• Some'are'Chemoautrophs'o Include'both'Bacteria'and'Achaeans.'Instead'of'sunlight,'they'make'energy'by'breaking'the'bonds'in'organic'chemicals'like'sulfur,'hydrogen,'nitride,'ammonia,'etc.'They'capture'the'energy'that'is'stored'there.'After'getting'the'energy'from'the'bonds,'they'break'down'C02,'as'a'carbon'source'to'make'sugars.'Found'in'abundance'at'the'sea'floor'in'extremely'hot'hydrothermic'vents.'Whole'ecosystems'survive'near'these'vents'where'there'is'no'sunlight.'All'the'species'there,'even'big'eukaryotes'(fish),'they'subsist'on'the'chemically'produced'energy'from'these'prokaryotes'(often'through'some'relationship'between'bacteria/Achaea'with'other'heterotrophic'organisms.)''• Some'are'Photoheterotrophs'o
View Full Document