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Bacteria
One of two prokaryotic domains, the other being Archaea
Peptidoglycan
A type of polymer in bacterial cell walls consisting of modified sugars cross-linked by short polypeptides
Gram-negative
Bacteria with walls that have less peptidoglycan and are more structurally complex, with an outer membrane that contains lipopolysaccharide (lipid connected to a long polysaccharide). Stain pink-red with gram stain
Gram-positive
Bacteria with relatively simple walls composed of a thick layer of peptidoglycan. Stain purple with gram stain
Endospore
A thick-coated, resistant cell produced by some bacterial cells when they are exposed to harsh conditions
Capsule
In many prokaryotes, a dense and well-defined layer of polysaccharide or protein that surrounds the cell wall and is sticky, protecting the cell and enabling it to adhere to substrates or other cells
Fimbriae
A short, hairlike appendage of a prokaryotic cell that helps it adhere to the substrate or to other cells
Nucleoid
A non-membrane-enclosed region in a prokaryotic cell where its chromosome is located
Plasmid
A small, circular, double-stranded DNA molecule that carries accessory genes separate from those of a bacterial chromosome
Conjugation
The direct transfer of DNA between two cells that are temporarily joined
Transformation
A change in genotype and phenotype due to the assimilation of external DNA by a cell
Transduction
A process in which viruses, known as phages, carry bacterial DNA from one bacterial cell to another
Thermophile
An organism that thrives at relatively high temperatures
Halophile
An organism that lives in a highly saline environment
Antibiotic resistance
The phenomenon where bacteria evolve to become resistant to the effects of drugs designed to kill them, often due to rapid reproduction and the spread of resistance genes within and among bacterial species, making infections harder to treat
Prokaryotes
Evolved around 4.1 billion years ago
Have had the most time to adapt, thriving in diverse and extreme environments
Are the most diverse and abundant group of organisms, classified into two domains: bacteria and archaea
Only about 2% of bacteria have been identified
Prokaryotic morphology & anatomy
Are primarily unicellular, though some bacteria are multicellular
They typically range from 0.5 to 5 micrometers in diameter, a small size that allows them to thrive in large numbers in limited spaces
Their shapes include coccus (spherical), bacillus (rod-shaped), and spirillum (spiral)
Biofilms
A surface-coating colony of one or more species of unicellular organisms that engage in a metabolic cooperation
Pili
In bacteria, a structure that links one cell to another at the start of conjugation
Flagella
A long cellular appendage specialized for locomotion. Are made of a motor, hook, and filament that are synthesized by 42 proteins
Taxis
An oriented movement toward or away from a stimulus
Chemotaxis
An oriented movement toward or away from a chemical stimulus
Internal anatomy of bacteria
Lack membrane-bound organelles
Ribosomes responsible for protein synthesis
A single, circular chromosome located in the nucleoid region of the cell
Contain plasmids
Highly folded plasma membrane
These membranes include the respiratory membrane for cellular respiration and the thylakoid membrane for photosynthesis
Archaea
Known for being extremophiles
Unique traits include membrane lipids with branched structures and the absence of peptidoglycan in their cell walls
Archaea share some characteristics with eukaryotes, such as similarities in DNA analysis, making them more closely related to eukaryotes than to prokaryotes
Life cycle of prokaryotes
1-3 hours before undergoing division
Binary Fission
A method of asexual reproduction in single-celled organisms in which the cell grows to roughly double its size and then divides into two cells
Mutation
The exchange, deletion, or insertion of one or more nucleotides in DNA
This process leads to genetic variation
Mutation rates in prokaryotes are not higher than in eukaryotes; however, due to their short life cycles, mutations can be incorporated into prokaryotic populations much more quickly
Conjugation using plasmid
Requires genes for protein production that allow material exchange, such as the F-plasmid
The F-plasmid creates a mating bridge by forming a pilus between two bacterial cells
The pilus extends, attaches, and retracts to bring the cells closer together
One strand of the F-plasmid is transferred from the donor (F+ cell) to the recipient (F- cell) through the mating bridge
The strands replicate, forming double strands, so both cells now contain the DNA from the F-plasmid
Conjugation using bacterial chromosomes
Requires the F-factor integrated into the bacterial genome
A pilus and mating bridge form between the two cells
A single strand of DNA is transferred from the donor to the recipient
Crossing over and recombination occur, incorporating the new DNA into the recipient's chromosome
Phototroph
An organism that uses light as its primary energy source
Chemotroph
An organism that obtains energy by the oxidation of electron donors in their environments
Autotroph
An organism that obtains organic food molecules without eating other organisms or substances derived from other organisms
Heterotroph
An organism that obtains organic food molecules by eating other organisms or substances derived from them
Photoautotroph
An organism that harnesses energy to drive the synthesis of organic compounds from carbon dioxide
Chemoheterotroph
An organism that requires organic molecules for both energy and carbon
Chemoautotroph
An organism that obtains energy by oxidizing inorganic substances and needs only carbon dioxide as a carbon source
Photoheterotroph
An organism that uses light to generate ATP but must obtain carbon in organic form
Aerobic respiration
A chemical process that uses oxygen to convert glucose into energy, carbon dioxide, and water
Anaerobic respiration
A process that produces energy without oxygen
Obligate aerobe
An organism that requires oxygen for cellular respiration and cannot live without it
Obligate anaerobe
An organism that carries out only fermentation or anaerobic respiration. Such organisms cannot use oxygen and in fact may be poisoned by it
Nitrogen fixation
The conversion of atmospheric nitrogen to ammonia
Heterocyst
A specialized cell that engages in nitrogen fixation in some filamentous cyanobacteria
Metabolic cooperation
Individual prokaryotic cells within a community share resources and metabolic processes, often by exchanging metabolites, allowing them to perform specialized functions and enhancing their collective survival, most commonly observed in biofilms
Methanogen
An organism that produces methane as a waste product of the way it obtains energy
Symbiosis
An ecological relationship between organisms of two different species that live together in direct and intimate contact
Mutualism
An ecological interaction that benefits individuals of both interacting species
Commensalism
An ecological interaction that benefits the individuals of one species but neither harms nor helps the individuals of the other species
Parasitism
An ecological interaction in which one organism, the parasite, benefits by feeding upon another organism, the host, which is harmed
Pathogen
An organism or virus that causes disease
Exotoxins
A toxic protein that is secreted by a prokaryote or other pathogen and that produces specific symptoms, even if the pathogen is no longer present
Endotoxins
When the lipopolysaccharides from the outer membrane of gram-negative bacteria are released when the bacteria die
Decomposition & Recycling
The breakdown of organic matter by bacteria and other organisms, releasing nutrients back into the environment. This process recycles carbon, nitrogen, and phosphorus: carbon is released as CO2 for photosynthesis, nitrogen returns as nitrate and nitrite, and phosphorus is recycled similarly. Humans utilize bacteria in bioremediation and sewage treatment to break down waste. Additionally, bacteria help degrade biodegradable plastics, and some bacteria can absorb metals for environmental cleanup
Facultative anaerobe
An organism that makes ATP by aerobic respiration if oxygen is present but that switches to anaerobic respiration or fermentation if oxygen is not present
Fermentation
An anaerobic process in which energy can be released from glucose even if oxygen is not available
Horizontal Gene Transfer (HGT) or Lateral Gene Transfer
The transfer of genes from one genome to another through transformation, transduction, and conjugation
