Prokaryotes Flashcards
History of microbiology #2
History of microbiology #2
- Antony van Leeuwenhoek was first to observe and accurately describe microbial life
- Modern electron microscopes allows the study of cell substructure
- Louis Pasteur refutes idea of spontaneous generation (idea that living things arise spontaneously from other living thins)
History of microbiology #3
- Robert Koch studied anthrax; proposed four postulates to prove a casual relationship between a microorganism and a disease
- ## 1) the microorganism
Prokaryotic Diversity
- Oldest, structurally simplest, and most abundant forms of life
- Abundant for over a billion years before eukaryotes appeared
- 90-99% unknown and undescribed
- Fall into 2 domains
- Bacteria
- Archea
- Manu archea are extremophilies
Characteristics of Prokaryotes #1
- Unicellularity
- most are single-celled
- May stick together to form associations and biofilms
- Cell size
- Size varies tremendously
- Most are less than 1 um in diameter
- Nuceloid
- Chromosome is single circular double-stranded DNA
- Found in the nucleoid region of cell
- often have plasmids
- Cell division
- Most dicide by binary fission
Characteristics of prokaryotes #2
- Genetic recombination
- Exchange genetic material Extensively Through horizontal gene transfer; not a form of reproduction
- Internal Compartmentalization
- No membranse-bounded organelles
- No internal compartment
- Plasma membrane can be extensively infolded
- Flagella
- Simple in structure
- Different from eukaryotic flagella
- Metaboliv
Bacteria and archea differ fundamentally
- They differ in four key areas
Bacteria vs Archea
Earl classification characteristics
- Prokaryotes not easily classified according to forms
- Early systens relied on staining characteristics and observable phenotypes
1) Photosynthetic or nonphotosynthetic
2) Motile or nonmotile
3) Unicellular, colony-forming, or filamentous
4) formartion of spores or division by tranverse binary fission
5) Importance as human pathogens or not
molecular classification #1
1) Amino acid sequences of key proteins
2) percent guanine-cytosine content
3) Nucleic acid Hybridization
- closely related species will have more base pairing
4) gene and RNA sequencing
- Especially rRNA
5) Whole- genome sequencing
Molecular Classification #2
- Based on these molecular data, several prokaryotic groupings have been proposed
- Bergey’s Manual of systematic Bacteriology
prokaryotic cell structure
3 basic shapes
- Bacillus- Rod shaped
- Coccus- Spherical
Prokaryotic cell walls #1
1) Gram positive bacteria
- Thick, compled network of peptidoglycan
- Also contains Lipoteichoic and teichoic acid
2) Gram negative bacteria
- Thin layer of peptidoglycan
- Second outer membrane with lipopolysaccharide
- Resistanr to many antibiotics
Prokaryotic cell characteristics
1) Cell wall
- Peptidoglycan forms a rigid network
- mantains shape
- withstands hypotonic enviromenmts
- Archea have a similar molecule (pseudomurein)
2) Gram
Prokaryotic cell walls #2
1) Slayer
- rigid paracrystalline layer found in some bacteria and archea
- Outside of peptidoglycan ir outer membrane layers in gram-negative and gram-positive bacteria
- Diverse function-often involves adhesion
2) capsule
- gelatinous layer found in some bacteria
- Aids in attatchment
- Protects from the immune system
Bacterial flagella and pili
1) Flagella
- Slender, rigid,
Endospores
- Develop a thick wall around their genome and a small portion of the cytoplasm when exposed ti envirionmental stress
- Highly resistant to enviromental stress
-> Especially heat - When conditions improve can germinate and return to nomal cell division
- Bacteria cauding tetanus, botulism, and anthrax
Organization of prokaryotics cell
- Nucleid region
- Contains the single circular chromosomes
Prokaryotes cells often have complex internal membranes
Prokaryotic Genetics
- Prokaryotes do not reproduce seexually
- 3 types of horizontal gene transfer
- Conjufatiion- cell to cell contact
- Transduction- bu viruses
- Transformation- from the environment
- All 3 processes also observed in archea
F plasmid transfer
- F+ cell produces F pilus that connects it to F- Cell
- Trnsfers
Conjugation
- plasmids may encode functions not necessary to the organism, but may provide to the organism, but nmay provide a selective advantage
- In E.Coli, conjugation is based on the precense
Transduction
- Generalized transduction
- Virtually any gene can be transferred
- Occurs via accidents in the lytic cycle
- Viruses package bacterial DNA and transfers it in a subsequent infectiomn
-2) Specialized. transduction - Occurs via accidents in the lysogenic cycle
- Imorecise exicison of prophage DNA
Transformation
- Ocurs in many bacteria; species, including Streptococcus which was studied by griffith
- DNA that is release dfrom a dead cell is picked up by another llive cell
- Proteins involved in natural transformation encoded
Artifical transformation
- some species do not naturally undergo transformation
- Accomplished in the lab
Antibiotic resistance
- R (resistance) Plasmids
- Encode antibiotic resistance genes
Mutation in bacteria
- Mutations can arise spontaneously in bacteria as with any organism
- radiation and chemical increase likelihood
- Auxotrophs are nutritional mutants
- can not longer survive on mminimal
Antibiotic resistance
- R(resistance) plasmids
- Encode antibiotic resistance genes
- Acquired resistance genes
- Acquired genes through transposbale elemnts
- Importance factor in appearance
prokaryotic metabolism
- Acquisition of carbon
- Autpthopds- form inorganic CO2
- Photautothops- energy from oxidizing inorganic substances
- Heterothrophs- from organic molecules
- Photoheterotroph- both
Human Bacterial disease
- In the early 20th century, infectious diseases killed 20% oif children before the age of five
- Sanitation and antibiotics considerably imroved the situation
- In recent years, however, many bacterial diseases have appeared and reappeared
