Topic 6: Prokaryotes ✅ Flashcards
3 domains of life
Bacteria
Archaea
Eukarya
Eukarya kingdoms
Protists
Fungi
Plants
Animals
Where do you find unicellular prokaryotes?
Domain Bacteria and Domain Archaea
Prokaryotic Microorgnisms
Archaea
Bacteria
Eukaryotic microorganisms
Protists
Fungi
Prokaryotic macroorganisms
Don’t exist
Eukaryotic macroorganisms
Animals
Plants
Micro-organisms definition
Microscopic organisms
Consist of either 1 cell (unicellular) or a group of cells (multicellular)
Microorganism categories
Bacteria
Archaea
Protists
Fungi
Viruses
Unicellular prokaryotic microorganisms
Bacteria
Unicellular prokaryotic microorganisms
Archaea
Eukaryotic microorganisms
Protists
Eg Protozoa, algae
Fungi
Eg yeasts, mushrooms
Non-cellular pathogens
Viruses
What do pathogenic micro-organisms cause?
Infectious diseases
Pasteur’s relevance
1870
-discovered role of pathogenic bacteria in transmission of infectious diseases
Koch’s relevance
1892
-discovered Vibrio cholarae as the pathogen that causes cholera
Which pathogen causes cholera?
Vibrio cholerae
Alexander Fleming’s relevance
1929
-Discovered the antibiotic penicillin
Examples of outbreaks of pandemics that were viral
HIV
Flu pandemic
Asian Flu
Examples of bacterial pandemic outbreaks
6th cholera pandemic
Black death
What pathogen caused the plague (aka the Black Death)?
Yersinia pestis bacterium
How did Fleming make his discovery?
Accidentally discovered a mold growing in his lab
-it was capable of killing the bacterium “staphylococcus aureus”
Ernest Chain and Howard Florey relevance
1940ish
Purify and isolate penicillin from its mold
-> life-saving drug
Quarantine word origin
From phrase quarantina giorni meaning 40 days
Prokaryotes size relative to eukaryotes
Smaller
Domain bacteria categories
Eubacteria: includes pathogenic bacteria
Cyanobacteria: non-pathogenic, have chlorophyll & perform photosynthesis
Where do Cyanobacteria live?
Lakes, oceans etc
Cyanobacteria role in..
In nitrogen fixation
->ie converting nitrogen to ammonia
Also, have chlorophyll and perform photosynthesis ->produce oxygen
Where do archaea live?
Extreme conditions
-Halophiles in stately lakes
-Methanogens (anaerobes, produce methane) in digestive track
-Thermoacidophiles in acidous, sulphur-rich hot springs (optimum: 70-80 C, pH 2-3)
Taxonomy
Classification of living organisms
Dirty Kevin Periodically Calls Out For Gay Sex
-domain
-kingdom
-phylum
-class
-order
-family
-genus
-species
After Species in taxonomy
Subspecies
Variety
Strain (in bacteria)
Binomial Nomenclature
Carolus Linnaeus
1707-1778
Species name: genus + characteristic property
Prokaryotic cell size
1-10 micro-meter
Eukaryotic cell size
10-100 micro-meters
Variable morphology
Variety of shapes
Morphology of prokaryotes
Spherical shape (cocci) eg staphylcocci, streptococci)
Rod-shaped (rods) eg bacilli (eg E. Coli)
Spiral shape eg vibrio cholerae (C or S shape), Spirilla and Spirochetes
Difference between prokaryotic and eukaryotic cells
Prokaryotic:
-smaller
-no nuclear membrane
-no membrane-bound organelles (eg mitochondria, chloroplasts)
-no organized replicative cell cycle (mitosis)
-replicate by binary fission
-cell wall has different composition
-nucleoid, cell wall, cytoplasm, cytoplasmic membrane etc)
Cell wall function in prokaryotes
-maintain cell shape
-protects the cell
-prevents cell from bursting in hypotonic environment (osmotic pressure)
-role in cell division
Eukaryotic cell wall composition
-Cellulose (plant cells)
Or
-Chitin (fungi)
Bacterial cell walls contain?
Peptidoglycan
-a network of polysaccharides and polypeptides
(NAM, NAG, OLIGOPEPTIDE CHAIN AND GLYCINE RESIDUES)
Archaea cell walls contain?
Polysaccharides and proteins but not peptidoglycan
Gram staining
Staining technique
-used to classify bacteria in 2 major categories (based on cell wall comparison)
Crystal violet dye used
Gram positive bacteria
Cell wall consists of mostly peptidoglycan
-absorb crystal violet =>purple colour
Gram negative bacteria
Cell walls consist of a small amount of peptidoglycan and large amount of lipopolysaccharides (LPS)
-don’t absorb crystal violet=> pink colour
Examples of gram+ bacteria
Staphylococci
Streptococci
Micrococci
Gram+ cell wall structure
In peptidoglycan:
-blocky pieces: wall-associated protein
-short & skinny: teichoic acid
Gram- bacteria cell wall structure
Peptidoglycan and outer LPS membrane
Periplasm
Peptidoglycan and lipoproteins
Space between inner and outer membrane
Gram(-) examples
E. Coli, shigell, salmonella
Difference between gram+ and gram-
(+)
-peptidoglycan cell wall
=>resistant to physical stress
=>sensitive to lysozyme and penicillin
(-)
-outer lipopolysaccharide layer
=>resistant to lysozyme and penicillin
=>many antibiotics (eg penicillin) target the peptidoglycan and damage bacterial cell walls
=>gram(-) bacteria are more likely to be antibiotic resistant
Capsule
Only on some
Polysaccharide or protein layer that covers some prokaryotes on external of cell walls
Associated with the increased virulence of pathogenic bacteria
Virulence
Severity to cause disease
Capsule function
Protects from:
-phagocytosis by leukocytes
-from digestion upon phagocytosis
-from infection by phases and drying
Fimbriae
Only some have 1-4000 per bacterium
Function is attachment of bacteria to each other or to other cells that they infect
Sex pili
Special type of fimbriae (longer than regular) that allow prokaryotic DNA exchange
Conjugation
Genetic material transfer between prokaryotic cells through sex pili
Unidirectional process- one cell gives the DNA the other cell receives
-used for plasmid transfer from one bacterium to the other
The donor cell attaches to a recipient by a pilus, pulls it closer and transfers DNA
Plasmids
Small circular extrachromosomal DNA molecules
Some carry genes responsible for antibiotic resistance (R plasmids)
F plasmid
Required for the production pili
Bacteria that have it act as DNA donors
R plasmids
Carry genes for antibiotic resistance
Bacteria with specific R plasmids are resistant to certain antibiotics
Natural selection favors genes for resistance in population exposed to antibiotics
Antibiotic-resistant strains of bacteria are becoming more common
Motility of prokaryotes
Taxis: ability of bacteria to move toward or away from a stimulus
Chemotaxis: movement toward or away from a chemical stimulus
Prokaryotic motility structures:
-flagella (most bacteria)
-axial filaments (in spirochetes)
-polysaccharides (in flexibacter polymorphus)
Flagella
Bacterial motility structure
May be scatter or concentrated on end(s)
Flagella do Bacteria, Archaea and Eukaryotes are composed of different proteins
Movement type: rotation- CW or CCW
Category of bacteria depending on location of flagella
Monotrichous: 1, eg vibria
Lophotrichous: multiple at 1 end, eg Spirilla
Amphitrichous: single on either end
Peritrichous: multiple flagella projecting in all directions, eg E. Coli, Clostridium Parabotulinum
Prokaryotic flagellum structure
- Motor: responsible for rotation
-located within cell wall and plasma membrane
-energy for rotation comes from proton motive force (H+ pump) - Hook: located just outside of cell wall
- Filament: subunits of the protein flagellin, CW or CCW rotation
Axial filaments
In spirochetes
Twisting motion like a snake
In periplasmic space
Semipermeable membrane
Has phospholipids and proteins like eukaryotes
Internal organisation and DNA
Prokaryotic cells lack membrane-bound organelles
Have mesosomes
-infoldings of plasma membrane
-specialized membranes that perform metabolic functions in some prokaryotes
Function:
-cellular respiration (in aerobic prokaryotes) or photosynthesis (in cyanobacteria)
-formation of diaphragm during cytokinesis
Prokaryotic ribosomes
RNA + mRNA
Function is protein synthesis
Prokaryotic ribosomes consist of different subunits than eukaryotes
30S (small subunit) and 50S (large) subunits
->antibiotics like tetracycline inhibit bacterial ribosomes without inhibiting human ribosomes
Nucleoid
Region that contains prokaryotic chromosomes lacking nuclear membrane
Polysome
Ribosomes + mRNA
Prokaryotic chromosome
Double-stranded circular DNA molecule
Smaller than eukaryotic genome
-absence of histones
-supercoiled to fit the nucleoid region
Prokaryotes may contain extra-chromosomal regions:
-plasmids
-bacteriophages
Plasmids
Small circular DNA molecules (R plasmids)
(Bacterio)phages
Viruses that infect bacteria (have DNA genome)
Endospores
Sporogenic prokaryotes have the ability to form endospores
Formed under harsh conditions (very high or low temp or dry environment)
Resistant to temp, dryness, UV light, enzymes, chemicals and drugs
Can grow back yo prokaryotic (vegetative) cell once in optimal conditions
Eg of sporogenic bacteria
Bacilli
Clostridia
Bacillus Atrhus
Prokaryote groups based on nutrition
Based on energy and carbon source
Phototrophs, chemotrophs, autotrophs, heterotrophs
Chemotrophs
Obtain energy from chemicals
Chemoautorophs:
-energy source= inorganic chemicals (eg H2S, NH3, FE2+
-carbon source= CO2, HCO3- ETC
-Certain prokaryotes (eg purple-sulphuric bacteria)
Chemoheterotrophs:
-organic compounds
-organic compounds
-many prokaryotes (eg Clostridium) and protists; fungi, animals, some plants
Prokaryotic cell structure
Cell wall: protect from mechanical damage and osmotic pressure
Cell plasma membrane: semi-permeable so controls what enters ands exits
Capsule (only some): protects bacteria from phagocytosis/ digestion/ drying
Fimbriae (only some): attach bacteria to each other or to host
Sex pili (some): allows prokaryotes to exchange DNA
Flagella (some): motility
Nucleoid: where bacterial chromosome is found
Genetic recombination
Combination of DNA from 2 sources
Contributes to genetic diversity
Horizontal gene transfer
Movement of genes among individuals from different species
=>prokaryotic DNA from different individuals can be brought together by
Transformation
Uptake and incorporation of foreign DNA by prokaryotic cells from their surroundings
Transduction
Exchange of DNA between bacteria mediated by bacteriophages (viruses that infect bacteria)
Conjugation
Transfer of genetic material between prokaryotic cells in direct contact
Through six pili
Binary fission
- Chromosome replication begins
-one copy of the origin moves rapidly towards the other end of the cell - Replication continues
-one copy of the origin is at each end of the cell - Replication finishes
-plasma membrane grows inward, new cell wall is deposited - Two daughter cells result
Oxygen metabolism
Prokaryotes categorized based on ability to metabolize gas
Obligate aerobes
Obligate anaerobes
Facultative anaerobes
Nitrogen is essential
Major groups of bacteria
Phyla
- Protebacteria
- Chlamydia
- Spirochetes
- Cyanobacteria
- Gram-positive bacteria (the rest are neg)
Group 1
Gram(-)
5 subcategories: Alpha, Beta, Gamma, Deta, Epsilon.
Only EPSILON is fully pathogenic, rest have environmental roles
Alpha Proteobacteria
Subgroup
Many perform symbiosis aka are closely associated with eukaryotic hosts
Mitochondria have evolved from aerobic alpha-proteobacteria through endosymbiosis
Beta proteobacteria
Non-pathogenic and pathogenic
Pathogenic= Neisseria morphology (diplococci)
-Neisseria meningitidis (meningococcus): causes meningococcal meningitis
-Neisseria gonorrhea (gonococcus): causes gonoccocal urethritis (gonnorrhea STD)
-Bordetella pertussis: causes whooping cough (pertussis)
Diplococci
2 spheres in a gram strain
Gamma proteobacteria
Pathogenic: Legionella, salmonella (rod shaped (EM) and Vibrio Cholera
Opportunistic pathogens: Escherichia Coli is normally part of intestinal flora but it can cause opportunistic infections in immunosuppressed individuals (AIDS)
Vibrio cholera: causes cholera due to toxin production (enterotoxin) -> dehydration then death
-symptoms: prolonged diarrhoea (5-15 days)
Transmitted via contaminated, non-chlorinated water in underdeveloped countries
Delta proteobacteria
Subgroup
Non pathogenic
Epsilon proteobacteria
Pathogenic subgroup
Campylobacter: causes food poisoning (complications: blood poisoning)
Helicobacter pylori: causes stomach ulcers and gastric cancer, gastritis
Chlamydias
Obligate parasites that live in animal cells
Chlamydia trachomatis: causes non-gonococcal urethritis (sexually transmitted disease), if prolonged; scarring of Fallopian tubes ->infertility
Spirochetes
Leptospirosis
Spiral-shaped bacteria
Borrelia burgdorferi: causes Lyme disease
Treponema pallidum: causes syphilis (STD)
Symptoms of leptospirosis:
-zoonosis: if transmitted by animals (rodents)
-jaundice due to liver infection
-kidney infection
Cyanobacteria
Non-pathogenic
Endosymbiotic theory: chloroplasts likely evolved from Cyanobacteria by endosymbiosis
Gram(+) bacteria
Includes several pathogenic species:
-Actinobacteria (Actinomycetes): soil decomposers, cause cutaneous infections
-Bacillus anthracis: causes anthrax (rod and chain morphology)
-Corynebacteriuim diphtheriae: causes diptheria
-Clostridium botulinum: causes botulism (contaminates improperly canned food)
-Clostridium tetani: causes tetanus
-several Staphylococcus and Streptococcus species (eg Staphylococcus aureus, Streptococcus pneumoniae)
-Mycobacteria: Mycobacterium tuberculosis and Mycobacterium leprae
-Mycoplasmas: smallest known cells (no cell wall)
Clostridium botulinum
Contaminates improperly canned food
Produces the neurotoxin Boulinum toxin (botox)=> causes botulin
Causes paralysis by inhibiting the release of the neurotransmitter acetylcholine at the neuromuscular junction synaptic cleft
Death due to respiratory muscular failure
Clostridium tetani
Causes tetanus (Greek for stretch)
Symptoms: convulsive muscle spasms (convulsions of skeletal muscle) and paralysis
Due to toxin, can be fatal if untreated
Transmission: bacteria enter through a break in the skin (cut/puncture wound) by a contaminated object
Corynebacterium diptheriae
Causes diphtheria, a serious upper respiratory tract infection
Characteristic symptoms: Pseudomembrane formation in the pharynx, trachea etc
Diphtheria toxin inhibits protein synthesis (translations) =>cell/tissue and organ damage
Mycoplasmas
Gram(+) bacteria
Mycoplasma hominis and Ureaplasma urealyticum
Causes non-gonococcal urethritis
Mycobacteria and mycoplasmas
Both genera include species that are phylogenetically Gram+ but structurally neither gram+ or gram(-) according to the wall
They dont absorb the crystal violet dye
Mycoplasmas explanation
Don’t have a cell wall so can’t be classified as gram- or + according to the wall
Mycobacteria explanation
Have a unique lipid-rich (waxy) cell wall
->don’t have LPS outer layer that gram(-) bacteria have
Classified as acid-fast gram+ bacteria due to their lack of an outer LPS layer
Use other dye types like methylene blue to stain
Prokaryotes roles in biosphere
Chemical recycling
Ecological interactions:
-symbiosis: ecological relationship in which 2 species live in close contact
Types of symbiotic relationship:
-mutualism: both benefit
-commensalism: one benefits while neither harming/helping the other
-parasitism: organism called a parasite harms but doesn’t kill its host
=>parasites that cause diseases are called pathogens
Beneficial prokaryotes
Mutualistic bacteria
Part of our normal flora
Many break down food that is undigested by our intestines (can’t be digested by our enzymes)
Horizontal gene transfer
Some pathogenic bacteria are potential weapons of bioterrorism (eg Bacillus athracis)
Prokaryotes in DNA technology
Engineering
E. Coli used in gene cloning
-Agrobacterium tumefaciens: used to produce transgenic plants (GMOs)
Bacteria can be genetically engineered to produce vitamins, antibiotics, and hormones (eg insulin production)
