Prokaryotes - Chapter 23 (PDF)

Chapter 23: Prokaryotes David M. Phillips/Science Source © McGraw Hill, LLC 1  Prokaryotes Small, simple, and most abundant forms of life ~originated on earth over...

Chapter 23: Prokaryotes David M. Phillips/Science Source © McGraw Hill, LLC 1  Prokaryotes Small, simple, and most abundant forms of life ~originated on earth over 3.5 billion years ago Our knowledge of early life comes from microfossils 2 domains Bacteria: Early cyanobacteria produced oxygen which allowed for diversity Archaea: Earliest discovered were extremophiles Two of the three domains of life © McGraw Hill, LLC 2  Archaea and Bacteria Bacteria are as different from archaea as they are from eukaryotes (a): SPL/Science Source (b): BSIP SA/Alamy Stock Photo Access the text alternative for these images © McGraw Hill, LLC 3  Three Domains of Life Two domains are not closely related prokaryotes Archaea more closely resemble eukaryotes than bacteria based on rRNA sequences. Access the text alternative for these images © McGraw Hill, LLC 4  Prokaryote Characteristics Unicellularity Cell division single-celled, may stick together to form Most divide by binary fission associations/biofilms (asexual reproduction) No extensive membrane-bounded organelles Genetic recombination Occurs through horizontal gene Cell size transfer Varies; Most are less than 1 µm in diameter Not a form of sexual reproduction Chromosomes Flagella Single circular chromosome Single protein fiber often have plasmids-small, circular, double- rotates like propellers stranded DNA molecules that are separate from chromosomal DNA and can replicate Metabolic diversity independently Oxygenic and anoxygenic photosynthesis Chemolithotrophic © McGraw Hill, LLC 5  Membrane Lipids Bacteria Fatty acid chains joined to glycerol phosphate with ester linkages Stereoisomer of glycerol-3- phosphate Membranes are unbranched and are diethers Access the text alternative for these images © McGraw Hill, LLC 6  Archaea Membrane Lipids Non-polar hydrocarbons called isoprenoids joined to glycerol phosphate with ether linkages Stereoisomer of glycerol-1- phosphate Membranes can be branched, in cyclic compounds, and may be tetraethers that can form a monolayer membrane Access the text alternative for these images © McGraw Hill, LLC 7  Bacteria versus Archaea Cell wall Bacteria have peptidoglycan Archaea lack peptidoglycan S-layer outside of wall or replacing wall Composed of glycoproteins that form a rigid paracrystalline surface Unique flagella Evolved independently from bacterial flagella © McGraw Hill, LLC 8  Bacteria versus Archaea DNA replication Both have single replication origin Archaeal initiation proteins are more similar to of eukaryotes' Gene expression Both have transcription-translation coupling Machinery is more similar to that of eukaryotes © McGraw Hill, LLC 9  Bacteria versus Archaea Methanogenesis All organically produced methane comes from archaea Ammonia oxidation Aerobic ammonia oxidation only found in archaea **Major contributor to global nitrogen cycle © McGraw Hill, LLC 10  Prokaryotic Cell Structure Bacteria have 3 basic shapes Bacillus – Rod-shaped Coccus – Spherical Spirillum – Helical-shaped (bacillus): Dr. Gary Gaugler/SPL/Science Source; (coccus): CNRI/Science Source; (spirillum): Centers for Disease Control and Prevention Access the text alternative for these images © McGraw Hill, LLC 11  Cell Wall Peptidoglycan forms a rigid network Unique to bacteria Maintains shape Withstands hypotonic environments Gram stain Gram-positive bacteria have a thicker peptidoglycan wall and stain a purple color Gram-negative bacteria contain less peptidoglycan and do not retain the purple color Counterstain to appear dark pink © McGraw Hill, LLC 12  The Gram Stain (b): Lisa Burgess/McGraw Hill © McGraw Hill, LLC 13  Gram Negative versus Positive Gram positive bacteria Thick, complex network of peptidoglycan Also contains lipoteichoic and teichoic acid Gram negative bacteria Thin layer of peptidoglycan Second outer membrane with lipopolysaccharides Resistant to many antibiotics © McGraw Hill, LLC 14  Capsule Gelatinous layer found in some bacteria Surrounds the cell wall Aids in attachment Protects from the immune system © McGraw Hill, LLC 15  Bacterial Flagella and Pili Flagella Slender, rigid, helical structures Composed of the protein flagellin Involved in locomotion – spins like propeller Pili Short, hairlike structures Found in gram- negative bacteria Aid in attachment and conjugation © McGraw Hill, LLC 16  Endospores Develop a thick wall around their genome and a small portion of the cytoplasm Form when exposed to environmental stress Highly resistant to environmental stress Especially heat When conditions improve can germinate and return to normal cell division Bacteria causing tetanus, botulism, and anthrax © McGraw Hill, LLC 17  Bacterial Cell Interior Prokaryotic cells often have complex internal membranes Invaginated regions of plasma membrane Function in respiration or photosynthesis (a): Dr. W.J. Ingledew/Science Source; (b): Biophoto Associates/Science Source Access the text alternative for these images © McGraw Hill, LLC 18  Bacterial Cell Interior Nucleoid region Contains the single, circular chromosome May also contain plasmids Small, independently replicating DNA Nonessential but can provide selective advantage Ribosomes Smaller than those of eukaryotes Differ in protein and RNA content Targeted by some antibiotics © McGraw Hill, LLC 19  Early Classification Characteristics Relied on staining characteristics and observable phenotypes Photosynthetic or nonphotosynthetic Motile or nonmotile Unicellular, colony-forming, or filamentous Formation of spores or division by transverse binary fission Importance as human pathogens or not © McGraw Hill, LLC 20  Molecular Classification Amino acid sequences of key proteins Nucleic acid hybridization Mixing of single-stranded DNA from two species Closely related species will have more base pairing Gene and RNA sequencing Whole-genome sequencing Several prokaryotic groupings have been proposed Large scale sequencing of random samples Incredible amount of diversity Indicates that the vast majority of bacteria have never been cultured or studied in detail © McGraw Hill, LLC 21  Clades of Prokaryotes 1 © McGraw Hill, LLC 22  Clades of Prokaryotes 2 © McGraw Hill, LLC 23  Prokaryotic Genetics 3 types of horizontal gene transfer Conjugation – mediated by plasmids Transduction – mediated by viruses Transformation – direct uptake of DNA **All 3 processes also observed in archaea © McGraw Hill, LLC 24  Conjugation 1 Plasmids may encode advantageous info Are not required for normal function In E. coli, conjugation is based on the presence of the F plasmid (fertility factor) F+ cells contain the plasmid F− cells do not (a) Dennis Kunkel Microscopy/Science Source Access the text alternative for these images © McGraw Hill, LLC 25  F+ plasmid: encodes protein subunits that assemble on the cell surface to form a hollow pilus binds to a site on the interior of the F+ cell near the pilus (conjugation bridge) replicated at the binding point (rolling-circle replication) 1 parental strand of plasmid DNA is displaced; strand transfers to recipient cell complementary strand is added, creating a new, stable F plasmid After successful transfer, the recipient cell becomes an F+ cell © McGraw Hill, LLC 26  Antibiotic Resistance R (resistance) plasmids Encode antibiotic resistance genes Acquire genes through transposable elements Selective advantage in the presence of antibiotics Antibiotic resistant strains of Staphylococcus aureus Virulence plasmids or transduction Encode genes for pathogenic traits E. coli O157:H7 strain arose this way © McGraw Hill, LLC 27  DNA Exchange through Horizontal Transmission Horizontal gene transfer can occur by: Conjugation Transduction (involves viruses) Transformation Access the text alternative for these images © McGraw Hill, LLC 28  Generalize Transduction Virtually any gene can be transferred Occurs via accidents in the lytic cycle Viral genome is packed into new phage heads If the machinery starts with a piece of bacterial DNA, it will be packed into the phage heads When viruses go on to infect another cell, they transfer the bacterial DNA and it can be incorporated by homologous recombination © McGraw Hill, LLC 29  Transformation Natural transformation DNA fragments are released from damaged or dead cells and are taken up by another live cell The new DNA is incorporated into the live cell's genome by homologous recombination Artificial transformation Some species do not naturally undergo transformation Can be accomplished in the lab Critical for gene cloning and DNA manipulation © McGraw Hill, LLC 30  DNA transfer by Hfr cells The F plasmid can integrate into the bacterial chromosome Similar to crossing over in eukaryotes Requires regions of homology These regions are called insertions sequences (IS) Exist both in the F plasmid and the E. coli chromosome Cells with the F plasmid integrated into chromosome are called Hfr cells (high frequency of recombination) Plasmid is replicated every time host divides © McGraw Hill, LLC 31  DNA transfer by Hfr cells Hfr cells can transfer chromosomal DNA during conjugation Portions of recipient chromosome can be replaced Origin of transfer is in the middle of the integrated plasmid Means that only a portion of the chromosome and F plasmid are transferred The F plasmid can also excise itself by reversing the integration process An inaccurate excision may occur picking up some chromosomal DNA – F′ plasmid Transfer of F′ plasmid results in partial diploids © McGraw Hill, LLC 32  Integration and Excision of F plasmid Access the text alternative for these images © McGraw Hill, LLC 33  Prokaryotic Metabolism - Autotrophs Photoautotrophs – energy from sun, convert inorganic CO2 to organic carbon Cyanobacteria Sulfur bacteria – use H2S as electron donor, anoxygenic Archaeal species use simple form of photosynthesis Bacteriorhodopsin moves protons across a membrane Chemolithoautotrophs – energy from oxidizing inorganic substances Nitrifiers oxidize ammonia or nitrite Prokaryotes in the deep ocean oxidize H 2S from thermal vents © McGraw Hill, LLC 34  Prokaryotic Metabolism - Heterotrophs Photoheterotrophs – light as energy source but obtain organic carbon made by other organisms Purple and green nonsulfur bacteria Chemoheterotrophs – both carbon atoms and energy from organic molecules Most prokaryotes Decomposers and most pathogens © McGraw Hill, LLC 35  Human Bacterial Disease In the early 20th century, infectious diseases killed 20% of children before the age of five Sanitation and antibiotics considerably improved the situation Examples: TB Agent: Mycobacterium tuberculosis Afflicts the respiratory system Easily transferred from person to person through the air 2017-1.6 millions died from the disease © McGraw Hill, LLC 36  Human Bacterial Disease In the early 20th century, infectious diseases killed 20% of children before the age of five Examples: Peptic ulcers Helicobacter pylori is the main cause Treated with antibiotics Dental caries (tooth decay) Plaque consists of bacterial biofilms Streptococcus sobrinus and S. mutans ferments sugar to lactic acid Tooth enamel degenerates, leaving tooth vulnerable to infection © McGraw Hill, LLC 37  Important Human Bacterial Diseases 1 TA B L E 2 3. 1 Important Human Bacterial Diseases Disease Pathogen Vector/Reservoir Epidemiology Anthrax Bacillus anthracis Animals, including Bacterial infection that can be transmitted through processed hides contact or ingestion; rare except in sporadic outbreaks; may be fatal Botulism Clostridium botulinum Improperly prepared food Contracted through ingestion or contact with wound; produces acute toxic poison; can be fatal Chlamydia Chlamydia Humans, sexually Urogenital infections with possible spread to eyes and trachomatis transmitted disease (STD) respiratory tract; increasingly common over the past 20 years Cholera Vibrio cholerae Human feces, plankton Causes severe diarrhea that can lead to death by dehydration; a major killer in times of crowding and poor sanitation Dental caries Streptococcus mutans, Humans A dense collection of these bacteria on the surface of Streptococcus teeth leads to secretion of acids that destroy minerals in sabrinus tooth enamel Diphtheria Corynebacterium Humans Acute inflammation and lesions of respiratory diphtheriae membranes; spread through respiratory droplets; vaccine available Gonorrhea Neisseria gonorrhoeae Humans only STD, on the increase worldwide, but left untreated it can be fatal Hansen disease Mycobacterium leprae Humans, feral armadillos Chronic infection of the skin; worldwide about 10–12 (leprosy) million infected; spread through contact with infected individuals © McGraw Hill, LLC 38  Important Human Bacterial Diseases 2 TA B L E 2 3. 1 Important Human Bacterial Diseases Lyme disease Borrelia burgdorferi Ticks, deer, small Spread through bite of infected tick; lesion rodents followed by malaise, fever, fatigue, pain, stiff neck, and headache Peptic ulcers Helicobacter pylori Humans Originally thought to be caused by stress or diet, most peptic ulcers now appear to be caused by this bacterium Plague Yersinia pestis Fleas of wild rodents: Killed 25% of European population in the 14th rats and squirrels century; endemic in wild rodent populations of western United States today Pneumonia Streptococcus, Humans Acute infection of the lungs; often fatal without Mycoplasma, treatment; vaccine for streptococcal pneumonia Chlamydia, available Haemophilus Tuberculosis Mycobacterium Humans, badgers Acute bacterial infection of the lungs, lymph, and tuberculosis meninges; incidence is on the rise, including antibiotic-resistant strains Typhoid fever Salmonella typhi Humans Systemic disease of worldwide incidence; fewer than 500 cases a year in the U.S.; spread through contaminated water or foods; vaccines available Typhus Rickettsia typhi Lice, rat fleas, Historically, a major killer in times of crowding and humans poor sanitation; transmitted through the bite of infected lice and fleas © McGraw Hill, LLC 39