Prokaryotic cells are tiny but mighty, packing a punch without fancy organelles. They're simpler than eukaryotes, with DNA floating freely and smaller ribosomes. But don't underestimate them – these little guys are incredibly diverse and adaptable.
From spheres to rods to spirals, prokaryotes come in all shapes and sizes. They've got tough cell walls, handy plasmids, and some even sport flagella for swimming. Bacteria and archaea may look similar, but they've got some key differences under the hood.
Defining Characteristics and Morphology of Prokaryotic Cells
Key features of prokaryotic cells
- Lack membrane-enclosed organelles resulting in DNA located directly in the cytoplasm, not within a nucleus
- Possess smaller ribosomes (70S) compared to eukaryotic ribosomes (80S) which are sites of protein synthesis
- Contain a single, circular chromosome with a generally smaller genome size relative to eukaryotes (E. coli, Streptococcus)
- May possess extrachromosomal DNA in the form of plasmids which are small, circular DNA molecules that replicate independently
- Cell wall present external to the cell membrane provides structural support and protection
- Peptidoglycan key component in bacterial cell walls (Staphylococcus aureus)
- Archaeal cell walls lack peptidoglycan and have distinct structures (pseudomurein, S-layer)
- Smaller in size compared to eukaryotic cells, typically ranging from 0.1-5 μm in diameter (Mycoplasma, Escherichia coli)
Shapes and arrangements of prokaryotes
- Shapes
- Cocci: spherical (Streptococcus)
- Bacilli: rod-shaped (Escherichia coli)
- Spirilla: spiral or curved (Spirillum)
- Vibrios: comma-shaped (Vibrio cholerae)
- Arrangements
- Diplococci: pairs of cocci (Neisseria)
- Streptococci: chains of cocci (Streptococcus pyogenes)
- Staphylococci: grape-like clusters of cocci (Staphylococcus aureus)
- Tetrads: square arrangement of four cocci (Micrococcus)
- Sarcinae: cube-like arrangement of eight cocci (Sarcina)
- Streptobacilli: chains of bacilli (Streptobacillus moniliformis)
Structure and Function of Prokaryotic Cell Components
Structure and function of prokaryotic components
- Cell envelope
- Cell membrane: phospholipid bilayer serves as a selective barrier controlling passage of substances
- Cell wall: provides structural support, protection, and maintains cell shape
- Gram-positive bacteria have a thick peptidoglycan layer (Bacillus)
- Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane (Salmonella)
- Capsule: external polysaccharide layer provides additional protection and aids in adherence to surfaces (Streptococcus pneumoniae)
- Cytoplasm: interior of the cell where metabolic reactions and processes occur
- Ribosomes: sites of protein synthesis, smaller (70S) than eukaryotic ribosomes
- Inclusions: storage granules for nutrients (glycogen, polyphosphate) and other substances
- Nucleoid: region where the single, circular DNA chromosome is located, not enclosed by a nuclear membrane
- Plasmids: small, extrachromosomal DNA molecules that can replicate independently and often carry genes for antibiotic resistance
- Pili and fimbriae: surface appendages involved in attachment to surfaces and DNA transfer during conjugation (F pilus)
- Flagella: long, whip-like structures used for motility, composed of flagellin protein (Escherichia coli)
Bacterial vs archaeal cell characteristics
- Similarities
- Both lack membrane-bound organelles
- Possess a single, circular DNA chromosome located in the cytoplasm
- Ribosomes (70S) are present in the cytoplasm for protein synthesis
- Differences
- Cell wall composition
- Bacterial cell walls contain peptidoglycan (murein)
- Archaeal cell walls lack peptidoglycan and may have pseudomurein, S-layer, or other unique structures
- Membrane lipids
- Bacterial membranes have ester-linked lipids
- Archaeal membranes have ether-linked lipids which are more stable in extreme conditions
- RNA polymerase
- Bacteria have a single type of RNA polymerase
- Archaea have multiple types of RNA polymerase, similar to eukaryotes
- Metabolic diversity
- Archaea exhibit unique metabolic capabilities, such as methanogenesis (methanogens) and survival in extreme environments (hyperthermophiles, halophiles)
- Cell wall composition
Prokaryotic Cell Processes
- Cell division: occurs through binary fission, where a single cell divides into two identical daughter cells
- Metabolism: diverse range of metabolic pathways for energy production and biosynthesis, including aerobic and anaerobic respiration, fermentation, and photosynthesis
- Motility: achieved through various mechanisms such as flagella, gliding, or twitching motility, allowing cells to move towards favorable environments or away from harmful ones
Key Terms to Review (134)
70S ribosome: The 70S ribosome is a type of ribosome found in prokaryotic cells, responsible for protein synthesis. It is composed of two subunits: the 50S large subunit and the 30S small subunit.
Active transport: Active transport is the movement of molecules across a cell membrane using energy, typically against their concentration gradient. This process is essential for maintaining cellular functions and homeostasis.
Amphitrichous: Amphitrichous describes bacteria that have a single flagellum on each of two opposite ends. This arrangement aids in their motility and ability to navigate through their environments.
Anabaena cylindrica: Anabaena cylindrica is a filamentous cyanobacterium known for its nitrogen-fixing abilities and unique cell differentiation. It forms chains of cells with specialized heterocysts that facilitate nitrogen fixation.
Anthrax: Anthrax is a serious infectious disease caused by the bacterium Bacillus anthracis. It primarily affects livestock but can also infect humans through contact with contaminated animal products.
Archaeal membrane: An archaeal membrane is a unique lipid bilayer that forms the boundary of archaeal cells, differing significantly from bacterial and eukaryotic membranes. It includes ether linkages and branched isoprenoid chains which contribute to its stability in extreme environments.
Archaeal cell walls: Archaeal cell walls are specialized structures that protect archaeal cells and provide shape, differing significantly from bacterial cell walls. They lack peptidoglycan and often contain unique polymers like pseudopeptidoglycan.
Bacterial cell walls: Bacterial cell walls are rigid structures that surround the cell membrane, providing shape and protection. They are primarily composed of peptidoglycan, a unique polymer found only in bacteria.
Bacteriochlorophylls: Bacteriochlorophylls are photosynthetic pigments found in certain phototrophic bacteria. They play a crucial role in capturing light energy for photosynthesis, distinct from chlorophyll found in plants.
Basal body: A basal body is a cellular structure that forms the base of a flagellum or cilium, anchoring it to the cell membrane. It is composed of microtubules arranged in a specific pattern and plays a critical role in the formation and function of these motile appendages.
Biofilms: Biofilms are complex communities of microorganisms that adhere to surfaces and are embedded within a self-produced matrix of extracellular polymeric substances. They provide protection to the bacteria from environmental stresses and antimicrobial agents.
Botulism: Botulism is a serious illness caused by the neurotoxin produced by Clostridium botulinum. It leads to muscle paralysis and can be life-threatening if not treated promptly.
Capsule: A capsule is a dense and well-defined layer of polysaccharides or proteins that surrounds the cell wall of some prokaryotic cells. It provides protection against environmental hazards and plays a role in pathogenicity.
Carboxysome: Carboxysomes are protein-shelled microcompartments found in cyanobacteria and some chemoautotrophs, which contain enzymes for carbon fixation. They enhance the efficiency of the Calvin cycle by concentrating carbon dioxide around rubisco.
Cell envelope: The cell envelope is a multi-layered structure that surrounds the cell membrane of prokaryotic cells, providing structural support and protection. It typically includes the cell wall, cell membrane, and sometimes an outer membrane.
Cell membrane: The cell membrane is a selectively permeable barrier that surrounds the cytoplasm of a cell, regulating the movement of substances in and out. In prokaryotic cells, it also plays a crucial role in energy generation and maintaining cellular homeostasis.
Cell wall: A cell wall is a rigid outer layer found in cells of plants, fungi, bacteria, algae, and some archaea. It provides structural support and protection, and helps maintain cell shape.
Chemotaxis: Chemotaxis is the movement of an organism or cell in response to a chemical stimulus. It plays a crucial role in bacterial movement and immune cell navigation towards infection sites.
Chlorophylls: Chlorophylls are green pigments found in the chloroplasts of plants and some prokaryotic cells, essential for photosynthesis. They absorb light most efficiently in the blue-violet and red parts of the electromagnetic spectrum.
Colitis: Colitis is the inflammation of the inner lining of the colon, often causing pain and diarrhea. It can result from infections, inflammatory bowel disease, or other causes.
Corynebacterium diphtheriae: Corynebacterium diphtheriae is a Gram-positive, non-motile bacterium that causes diphtheria, a serious respiratory disease. It produces a potent exotoxin that inhibits protein synthesis in host cells.
Crenation: Crenation is the process by which a cell shrinks and develops a scalloped or notched surface due to water loss through osmosis. This typically occurs when a cell is placed in a hypertonic solution.
Cyanobacteria: Cyanobacteria are a group of photosynthetic, gram-negative bacteria found in various aquatic environments. They play a significant role in oxygen production and nitrogen fixation.
Cytoplasm: Cytoplasm is the gel-like substance within the cell membrane, excluding the nucleus. It contains organelles, enzymes, and other vital components necessary for cellular functions.
Cytoplasmic membrane: The cytoplasmic membrane, also known as the plasma membrane, is a selectively permeable barrier that surrounds the cytoplasm of a cell. It plays a critical role in controlling the movement of substances in and out of the cell.
Endospores: Endospores are highly resistant, dormant structures formed by certain bacteria to survive extreme conditions. They can withstand heat, radiation, desiccation, and chemical damage.
Escherichia coli O157:H7: Escherichia coli O157:H7 is a pathogenic strain of the bacterium E. coli that can cause severe foodborne illness. It is characterized by its ability to produce Shiga toxin, leading to serious complications such as hemolytic uremic syndrome.
Eukaryotic cells: Eukaryotic cells are complex cells that contain a nucleus and various organelles enclosed within membranes. They are found in animals, plants, fungi, and protists.
F pilus: An F pilus, or sex pilus, is a hair-like appendage found on the surface of many bacteria that facilitates the transfer of DNA between cells during bacterial conjugation. It is primarily composed of the protein pilin and encoded by the F (fertility) plasmid.
Facilitated diffusion: Facilitated diffusion is a passive transport process where molecules move across the cell membrane via specific transmembrane proteins. It does not require energy and relies on the concentration gradient.
Fimbriae: Fimbriae are hair-like appendages present on the surface of many bacteria, primarily involved in adhesion to surfaces and other cells. They play a significant role in bacterial colonization and virulence.
Flagella: Flagella are long, whip-like structures that protrude from the cell body of certain prokaryotic and eukaryotic cells. They are primarily used for locomotion and can also serve sensory functions.
Fluid mosaic model: The fluid mosaic model describes the structure of cell membranes as a dynamic and flexible arrangement of lipids, proteins, and carbohydrates. This model emphasizes the lateral movement of components within the lipid bilayer.
Gas gangrene: Gas gangrene is a severe bacterial infection that produces gas within tissues. It is typically caused by Clostridium species, especially Clostridium perfringens.
Germination: Germination is the process by which a spore or seed begins to grow and develop into a new organism, often involving the resumption of metabolic activity. In microbiology, it is crucial for understanding how bacterial endospores return to an active state.
Glycocalyx: The glycocalyx is a gelatinous, sticky outer layer surrounding the cell wall of some bacteria. It functions in protection, adherence to surfaces, and interaction with the environment.
Gram-negative cells: Gram-negative cells are a type of bacteria characterized by their cell wall structure, which includes a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides. They do not retain the crystal violet stain used in Gram staining, appearing pink or red under a microscope.
Gram-positive cells: Gram-positive cells have thick peptidoglycan layers in their cell walls, which retain the crystal violet stain used in the Gram staining procedure. These cells appear purple under a microscope after the staining process.
Group A strep: Group A strep (Streptococcus pyogenes) is a gram-positive bacterium that causes various infections in humans. It is characterized by its ability to form chains and produce numerous virulence factors.
Halothiobacillus neapolitanus: Halothiobacillus neapolitanus is a sulfur-oxidizing bacterium that belongs to the Gammaproteobacteria class. It is known for its role in the biogeochemical cycling of sulfur and carbon.
Hypertonic medium: A hypertonic medium is an external environment where the concentration of solutes outside a cell is higher than inside the cell. This causes water to flow out of the cell, leading to cell shrinkage.
Hypotonic medium: A hypotonic medium is an extracellular environment where the concentration of solutes is lower than inside the cell. This can lead to water entering the cell through osmosis, potentially causing the cell to swell and burst.
Impetigo: Impetigo is a highly contagious bacterial skin infection characterized by red sores and blisters, primarily caused by Staphylococcus aureus and Streptococcus pyogenes. It commonly affects infants and young children but can occur in individuals of any age.
Inclusions: Inclusions are distinct intracellular structures found within prokaryotic cells that serve as storage vessels for nutrients, metabolic byproducts, and other substances. They help bacteria survive in fluctuating environmental conditions.
Isotonic medium: An isotonic medium is a solution where the concentration of solutes outside the cell is equal to the concentration inside the cell. This balance prevents the net movement of water into or out of the cell, maintaining cellular stability.
Lancefield: Lancefield classification is a system used to categorize certain types of bacteria, particularly streptococci, based on the carbohydrate composition of bacterial antigens found on their cell walls. This system is crucial for identifying pathogenic species and understanding their role in infections.
Lipopolysaccharide (LPS): Lipopolysaccharide (LPS) is a large molecule found in the outer membrane of Gram-negative bacteria. It plays a crucial role in bacterial pathogenicity and triggers strong immune responses in hosts.
Lophotrichous: Lophotrichous describes a bacterial cell having a tuft of flagella located at one or both poles. These flagella are used for movement in a liquid environment.
M protein: M protein is a virulence factor found on the surface of certain bacteria, notably Streptococcus pyogenes. It plays a crucial role in evading the host immune response by inhibiting phagocytosis.
Magnetosomes: Magnetosomes are intracellular structures in certain bacteria that contain magnetic iron minerals. They enable bacteria to orient themselves along the Earth's magnetic field.
Magnetospirillum magnetotacticum: Magnetospirillum magnetotacticum is a magnetotactic bacterium that orients itself along magnetic field lines using intracellular magnetic particles called magnetosomes. It is a model organism for studying magnetotaxis and the biochemistry of magnetosome formation.
Magnetotaxis: Magnetotaxis is the ability of certain microorganisms to orient and move along magnetic fields. This behavior aids them in navigating their environment, often to locate optimal conditions for growth.
Metachromatic granules: Metachromatic granules are intracellular storage bodies found in some prokaryotic cells, particularly in bacteria. They are typically composed of polyphosphate and can be stained to appear a different color from the dye used.
Monotrichous: Monotrichous describes a bacterium that has a single flagellum located at one of its poles. This flagellum is used for motility, allowing the bacterium to move in its environment.
Morphology: Morphology refers to the study of the form and structure of organisms. In microbiology, it particularly focuses on the shapes, sizes, and arrangements of prokaryotic cells.
Murein: Murein, also known as peptidoglycan, is a polymer that forms a protective layer outside the plasma membrane of most bacteria. It provides structural strength and shape to the cell.
Mycolic acids: Mycolic acids are long-chain fatty acids found in the cell walls of certain bacteria, notably Mycobacterium species. They contribute to the unique properties of these bacterial cell walls, such as resistance to desiccation and antibiotics.
Necrotizing fasciitis: Necrotizing fasciitis is a severe bacterial infection that destroys skin, fat, and tissue covering the muscles. It spreads rapidly and requires prompt medical intervention.
Nucleoid: The nucleoid is the irregularly-shaped region within a prokaryotic cell that contains most of the genetic material. Unlike a eukaryotic nucleus, it is not surrounded by a nuclear membrane.
Nucleoid-associated proteins (NAPs): Nucleoid-associated proteins (NAPs) are proteins that help in organizing and condensing the bacterial chromosome within the nucleoid. They play a crucial role in gene regulation, DNA replication, and cell division.
Osmosis: Osmosis is the passive movement of water molecules across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration. It is critical for maintaining cellular homeostasis.
Osmotic pressure: Osmotic pressure is the force exerted by solutes in a solution on a semipermeable membrane, driving the movement of water. It is crucial for maintaining cell integrity and function.
Outer membrane: The outer membrane is a lipid bilayer found in Gram-negative bacteria, serving as an additional protective barrier. It contains lipopolysaccharides that contribute to the structural integrity and defense against harmful substances.
Passive transport: Passive transport is the movement of molecules across cell membranes without the need for energy input. It relies on the concentration gradient to facilitate diffusion.
Peptidoglycan: Peptidoglycan is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria. It provides structural support and protection.
Periplasmic space: The periplasmic space is the area between the inner cytoplasmic membrane and the outer membrane in Gram-negative bacteria. It contains a gel-like matrix rich in enzymes and other proteins.
Peritrichous: Peritrichous refers to the arrangement of flagella distributed over the entire surface of a bacterial cell. It enables the bacterium to move in various directions more effectively.
Phospholipid-derived fatty acid analysis (PLFA): Phospholipid-derived fatty acid analysis (PLFA) is a method used to profile microbial communities by analyzing the phospholipid fatty acids in cell membranes. This technique helps characterize the structure and function of prokaryotic cells.
Pili: Pili are hair-like appendages found on the surface of many bacteria that facilitate attachment to surfaces and genetic exchange. They are essential for processes like conjugation and biofilm formation.
Photosynthetic bacteria: Photosynthetic bacteria are prokaryotic microorganisms that convert light energy into chemical energy through photosynthesis. They play a crucial role in ecosystems by producing oxygen and organic compounds.
Plasma membrane: The plasma membrane is a selectively permeable lipid bilayer that encloses the cytoplasm of a cell, controlling the movement of substances in and out. In prokaryotic cells, it also plays roles in energy generation and cellular processes.
Plasmid: A plasmid is a small, circular piece of DNA that exists independently of the chromosomal DNA in prokaryotic cells. Plasmids often carry genes that confer advantageous traits such as antibiotic resistance.
Plasmolysis: Plasmolysis is the process in which cells lose water in a hypertonic solution, causing the cell membrane to pull away from the cell wall. This often leads to cellular dehydration and reduced metabolic activity.
Polyhydroxybutyrate (PHB): Polyhydroxybutyrate (PHB) is a type of biopolymer produced by certain bacteria as an energy storage compound. It is a member of the polyhydroxyalkanoate (PHA) family and serves as an intracellular carbon reserve.
Prokaryotic cells: Prokaryotic cells are unicellular organisms that lack a nucleus and membrane-bound organelles. They have simple structures with genetic material found in the nucleoid region.
Pseudomonas aeruginosa: Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that can cause serious infections in humans. It is known for its resistance to antibiotics and ability to thrive in various environments.
Rat-bite fever: Rat-bite fever is an infectious disease caused by bacteria transmitted through the bite or scratch of a rodent or by ingesting food or water contaminated with rodent excreta. It is primarily caused by Streptobacillus moniliformis and Spirillum minus.
Rheumatic fever: Rheumatic fever is an inflammatory disease that can develop as a complication of inadequately treated strep throat or scarlet fever, caused by Group A Streptococcus bacteria. It primarily affects the heart, joints, skin, and brain.
Ribosomes: Ribosomes are molecular machines within cells that synthesize proteins by translating messenger RNA (mRNA) into polypeptide chains. They are composed of ribosomal RNA (rRNA) and proteins, and they exist in both prokaryotic and eukaryotic cells.
Runs: Runs are the straight-line movements exhibited by motile prokaryotic cells, typically in response to environmental stimuli. These are part of the chemotaxis process, where cells move toward or away from chemical signals.
S-layer: The S-layer (surface layer) is a crystalline array of protein or glycoprotein that covers the surface of many prokaryotic cells, providing structural support and protection. It is one of the outermost layers in these cells, often associated with cell wall integrity and interaction with the environment.
Scarlet fever: Scarlet fever is an infectious disease caused by the bacterium Streptococcus pyogenes, characterized by a red rash and high fever. It primarily affects children and can have serious complications if untreated.
Sex pilus: A sex pilus is a hair-like appendage found on the surface of many bacteria that facilitates genetic exchange during conjugation. It connects a donor bacterium to a recipient bacterium, enabling the transfer of DNA.
Simple diffusion: Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration without the need for energy input. It occurs across biological membranes and is driven by the concentration gradient.
Slime layer: A slime layer is a loosely organized, sticky layer outside the cell wall of some bacteria that provides protection and aids in adherence to surfaces. It is composed primarily of polysaccharides.
Spirillum minor: Spirillum minor is a Gram-negative, spiral-shaped bacterium known for causing rat-bite fever. It is typically transmitted through bites or scratches from infected rodents.
Sporulation: Sporulation is the process by which certain bacteria form endospores, allowing them to survive in harsh environmental conditions. This is a key survival mechanism for some prokaryotic cells.
Strep throat: Strep throat is a bacterial infection caused by Streptococcus pyogenes, characterized by inflammation and pain in the throat. It is highly contagious and spreads through respiratory droplets.
Streptococcus pneumoniae: Streptococcus pneumoniae is a Gram-positive bacterium often found in the human respiratory tract, capable of causing diseases such as pneumonia, meningitis, and sinusitis. It exhibits virulence factors like a polysaccharide capsule that help it evade the immune system.
Tetanus: Tetanus is a serious bacterial infection caused by Clostridium tetani, characterized by muscle stiffness and spasms. It commonly enters the body through wounds or cuts contaminated with the bacteria.
Toxic shock syndrome: Toxic shock syndrome (TSS) is a rare, life-threatening condition caused by bacterial toxins, primarily from Staphylococcus aureus and Streptococcus pyogenes. It leads to sudden high fever, rash, and multi-organ failure.
Tumbles: Tumbles are the erratic, random movements made by bacterial cells to change direction, typically caused by the reversal of flagellar rotation. This motion is part of the run-and-tumble behavior observed in prokaryotic cells during chemotaxis.
Vegetative cells: Vegetative cells are the metabolically active and growing phase of bacteria, as opposed to their dormant forms like spores. They perform essential functions such as nutrient uptake, metabolism, and cell division.
Volutin: Volutin, also known as metachromatic granules, are intracellular storage bodies found in some bacteria and yeasts. They store inorganic polyphosphate, which can be used for energy and other cellular processes.
Cocci: Cocci are a group of spherical-shaped prokaryotic cells that are commonly found in the domain Bacteria. They are one of the four main morphological groups of bacteria, along with bacilli (rod-shaped), spirilla (spiral-shaped), and vibrios (curved rods).
Spirilla: Spirilla are a type of spiral-shaped bacteria that belong to the domain Bacteria. They are characterized by their distinctive helical or corkscrew-like morphology, which is a unique feature among prokaryotic cells.
Bacteria: Bacteria are a vast and diverse group of single-celled microorganisms that are ubiquitous in the environment. They are prokaryotic cells, meaning they lack a true nucleus and membrane-bound organelles, and exhibit unique characteristics that distinguish them from other types of microorganisms. Bacteria play crucial roles in various habitats, relationships, and microbiomes, making them an essential component of the microbial world.
Archaea: Archaea are a domain of single-celled microorganisms that are distinct from bacteria and eukaryotes. They are prokaryotic in nature, but possess unique characteristics that set them apart from other prokaryotes, making them a separate domain of life. Archaea are found in a wide range of habitats, from extreme environments to the human microbiome, and have important applications in biotechnology and genetic engineering.
Nucleoid: The nucleoid is a region within a prokaryotic cell that contains the cell's genetic material, usually in the form of a single, circular chromosome. It is the primary site of genetic information storage and replication in bacteria and archaea, serving as the functional equivalent of the nucleus in eukaryotic cells.
Peptidoglycan: Peptidoglycan is a structural component found in the cell walls of most bacteria, providing them with shape, rigidity, and protection. It is a complex molecule composed of sugar and amino acid subunits that forms a mesh-like layer surrounding the bacterial cell membrane.
Gram-positive: Gram-positive bacteria are a group of prokaryotic cells that stain purple or dark blue when subjected to the Gram staining procedure. This characteristic is due to the unique structure of their cell wall, which is thick and composed primarily of peptidoglycan, a rigid polymer that provides structural support and protection to the cell.
Gram-negative: Gram-negative refers to a classification of bacteria based on their cell wall structure and response to the Gram staining technique. Gram-negative bacteria have a unique cell wall composition that distinguishes them from Gram-positive bacteria, with important implications for their characteristics and behavior.
Capsule: A capsule is a specialized structure found in some microorganisms, primarily bacteria, that serves as a protective layer surrounding the cell. It is a key feature that distinguishes certain prokaryotic cells and can also play a role in the virulence of eukaryotic pathogens.
Binary Fission: Binary fission is a type of asexual reproduction in which a single parent cell divides into two genetically identical daughter cells. This process is a fundamental characteristic of prokaryotic cells and a key mechanism by which microbes grow and proliferate.
Cytoplasm: Cytoplasm is the jelly-like substance that fills the inside of a cell, excluding the nucleus. It is the site of many essential cellular processes and provides the structural framework for the cell's organelles.
Cell Membrane: The cell membrane, also known as the plasma membrane, is a selectively permeable barrier that surrounds the cytoplasm of a cell. It acts as a gatekeeper, controlling the movement of substances in and out of the cell, while also providing structural support and maintaining the cell's shape.
Prokaryotic Cell: A prokaryotic cell is a type of single-celled organism that lacks a true nucleus and membrane-bound organelles. Prokaryotes are the simplest and oldest known form of life on Earth, and they exhibit several unique characteristics compared to eukaryotic cells.
Fimbriae: Fimbriae are thin, hair-like appendages that extend from the surface of some prokaryotic cells, particularly bacteria. They play a crucial role in the unique characteristics of prokaryotic cells as well as in the normal microbiota of the digestive system.
Pili: Pili, also known as fimbriae, are hair-like appendages that protrude from the surface of many bacterial cells. These thin, filamentous structures serve various functions in prokaryotic cells, including attachment, motility, and communication, and are closely associated with the unique characteristics of prokaryotes, their habitats, relationships, and the virulence factors of eukaryotic pathogens, as well as bacterial infections in the respiratory tract, digestive system, and nervous system.
Teichoic Acid: Teichoic acid is a type of glycopolymer found in the cell walls of most Gram-positive bacteria. It is a crucial component that contributes to the unique characteristics of prokaryotic cells, particularly in the context of their cell wall structure and function.
Plasmid: A plasmid is a small, circular, double-stranded DNA molecule found in the cytoplasm of many prokaryotic cells, such as bacteria and archaea. Plasmids are distinct from the main chromosomal DNA and can replicate independently, allowing them to be passed on to daughter cells during cell division. Plasmids play crucial roles in the unique characteristics of prokaryotic cells, the habitats and relationships of prokaryotes, and the structure and function of cellular genomes.
F Factor: The F factor, also known as the fertility factor, is a genetic element found in some bacteria that allows for the transfer of genetic material between cells through a process called conjugation. It is a crucial characteristic of prokaryotic cells that enables the exchange of genetic information, contributing to the diversity and adaptability of these microorganisms.
70S Ribosome: The 70S ribosome is a large, complex molecular machine found in the cytoplasm of prokaryotic cells, responsible for the synthesis of proteins essential for cellular function and growth. It is a key component of the unique characteristics that distinguish prokaryotic cells from their eukaryotic counterparts.
Mesosome: A mesosome is a specialized invagination or infolding of the cell membrane in prokaryotic cells, such as bacteria. Mesosomes are unique characteristics of prokaryotic cells and play important roles in various cellular processes.
Chemolithotrophy: Chemolithotrophy is a mode of nutrition in which organisms obtain energy by oxidizing inorganic chemical compounds, rather than by photosynthesis or the breakdown of organic compounds. These organisms, known as chemolithotrophs, are a type of prokaryote that play crucial roles in various ecosystems and biogeochemical cycles.
Haploid: Haploid refers to a cell or organism that contains a single set of chromosomes, as opposed to the diploid state which has two sets of chromosomes. Haploid cells are commonly found in the reproductive stages of organisms, playing a crucial role in sexual reproduction.
Pseudomurein: Pseudomurein is a unique structural component found in the cell walls of certain archaea, similar to the peptidoglycan (murein) found in bacterial cell walls, but with distinct differences in its chemical composition and linkages.
Vibrios: Vibrios are a genus of Gram-negative, curved or comma-shaped bacteria that belong to the family Vibrionaceae. They are known for their unique characteristics and are often associated with various prokaryotic cell features.
Diplococci: Diplococci are a distinctive form of bacteria that appear as pairs of round or oval-shaped cells. This unique characteristic is a defining feature of these prokaryotic microorganisms and has important implications for their habitats, relationships, and roles within microbiomes.
Streptococci: Streptococci are a genus of Gram-positive, spherical-shaped bacteria that often arrange in chains. They are a significant group of prokaryotes that exhibit unique characteristics and play important roles in various habitats and microbiomes.
Staphylococci: Staphylococci are a genus of Gram-positive, spherical-shaped bacteria that typically occur in clusters resembling grapes. They are known for their unique characteristics and their ability to thrive in diverse habitats, making them an important subject of study in the context of prokaryotic cells and microbial communities.
Tetrads: Tetrads are a unique cellular arrangement observed in some prokaryotic cells, where four cells are clustered together in a square-like formation. This distinct grouping is an important characteristic of certain prokaryotic species and is closely related to their cellular division and reproduction processes.
Sarcinae: Sarcinae are a group of spherical or cubical-shaped bacteria that divide in multiple planes to form characteristic clusters resembling bale-shaped packets or cubes. They are a unique characteristic of prokaryotic cells found in certain bacterial species.
F Pilus: The F pilus, also known as the sex pilus, is a specialized structure found on the surface of some prokaryotic cells, particularly Escherichia coli (E. coli). It plays a crucial role in the process of bacterial conjugation, which is a form of horizontal gene transfer that allows the exchange of genetic material between bacterial cells.
Streptobacilli: Streptobacilli are a type of rod-shaped bacteria that often occur in chains or clusters. They are classified as prokaryotic cells and exhibit several unique characteristics that distinguish them from eukaryotic cells.
Flagellin: Flagellin is a protein that forms the flagellum, a whip-like appendage found on the surface of many prokaryotic cells. It is a key structural component that enables bacterial motility and plays a crucial role in the unique characteristics of prokaryotic cells.
Methanogenesis: Methanogenesis is the process by which methane is produced as a byproduct of anaerobic respiration carried out by a specialized group of archaea known as methanogens. This unique metabolic pathway is a key characteristic of prokaryotic cells and a defining feature of the domain Archaea.
Methanogens: Methanogens are a group of archaea that are specialized in the production of methane gas through a unique metabolic process. They are anaerobic, meaning they can only survive in the absence of oxygen, and play a crucial role in various biogeochemical cycles.
Halophiles: Halophiles are organisms that thrive in high-salt environments, typically requiring at least 0.2 M (1.2%) sodium chloride for optimal growth. These specialized microbes have evolved unique adaptations to survive and function in conditions with elevated salinity.
Hyperthermophiles: Hyperthermophiles are a group of microorganisms that thrive in extremely hot environments, typically at temperatures above 80°C (176°F). These organisms possess unique adaptations that allow them to survive and grow in such extreme conditions, making them a fascinating subject of study in the fields of microbiology, extremophile biology, and evolutionary biology.
Hyperthermophiles are found in various environments, including deep-sea hydrothermal vents, hot springs, and geothermal areas, and they play a crucial role in the understanding of the origins of life and the limits of life on Earth. Their study is particularly relevant to the topics of 3.3 Unique Characteristics of Prokaryotic Cells, 4.5 Deeply Branching Bacteria, 4.6 Archaea, and 9.4 Temperature and Microbial Growth.
Chromosome: A chromosome is a thread-like structure found in the nucleus of a cell that carries the genetic information, or genes, in the form of DNA. Chromosomes are essential for the proper storage, organization, and transmission of genetic material in both prokaryotic and eukaryotic cells.
Cell Division: Cell division is the process by which a parent cell divides into two or more daughter cells, allowing for growth, repair, and reproduction in living organisms. This fundamental process is crucial for the maintenance and propagation of life, particularly in the context of prokaryotic cells.
Metabolism: Metabolism is the sum of all the chemical reactions that occur within an organism to sustain life. It involves the breakdown of complex molecules for energy (catabolism) and the synthesis of complex molecules from simpler ones (anabolism). Metabolism is a crucial aspect of both the unique characteristics of prokaryotic cells and the role of energy, matter, and enzymes in biological systems.
Motility: Motility refers to the ability of prokaryotic cells to move or propel themselves through their environment. This characteristic is crucial for various functions, such as seeking nutrients, avoiding threats, and facilitating interactions with other organisms.