Chapter 3 Flashcards
How organisms are different from eukaryotes
- the way their DNA is packaged: lack of nucleus and histones
- the makeup of their cell wall: peptidoglycan and other unique chemicals
- their internal structures: lack of membrane-bound organelles
- all are ubiquitous
- eukaryotes and some archaea wrap their DNA around histones
All bacterial cells posses:
- cytoplasmic membrane: it surrounds the cytoplasm and controls the flow of material in and out of the cell pool
- cytoplasm: a water-based solution filling the entire cell
- ribosomes: tiny particles composed of protein and RNA where protein synthesis occurs
- cytoskeleton: long fibers of protein that encircle the cell just inside the cytoplasmic membrane and contributes to the cells shape
One (or a few) chromosome(s)
Most bacterial cells possess
- cell wall: a semirigid casing that provides structural support and shape for the cell
- a surface coating called a glycocalyx: serves as protective, adhesive, and receptive functions. May fit tightly or be very loose and diffuse (slime layer)
Structures found in some, but not all bacterial cells
- flagella, pili, and fimbriae
- an outer membrane
- nanowires/nanotubes: allow bacteria t transmit electrons or nutrients to other bacteria or onto the environmental surfaces
- plasmids: double stranded DNA circles containing extra genes
- inclusions
- endospores
- microcompartments
- most of these are observed in archaea as well
Many bacteria function as independent single-celled, unicellular organism
- some act as a group in colonies or biofilms
- some communicate through nanotubes
-> bacteria have an average size of 1 micron
Cocci: circumference of 1 micron
Rods: length of 2 microns and a width of 1 micron
Pleomorphism
Variations in cell wall structure caused by slight genetic or nutritional differences
Bacterial shape coccus
- if the cell is spherical or ball-shaped, the bacterium is described as a coccus
- cocci can be perfect spheres, but they can also exist as oval, bean-shaped, or even pointed variants
Bacterial shape Bacillus
A cell that is cylindrical is termed a rod, or bacillus
- there is also a genus named bacillus
- rods are quite varied in their actual form
- depending on the species, they can be blocky, spindle-shaped, round-ended, and threadlike (filamentous), or even club-shaped or drumstick-shaped
- when a rod is short and plump, it is called a coco bacillus
Bacteria shape Vibrio
- singly occurring rods that are gently curved are called vibrio
Bacterial shape Spirillum
- a bacterium having a slightly curled or spiral-shaped body is called a spirillum
- a rigid helix, twisted twice or more along its axis (like a corkscrew)
Bacterial shape Spirochete
- another spiral cell (which contains periplasmic falgella) is the spirochete
- a more flexible form that resembles a spring
Bacterial shape Filaments
- a few bacteria produce multiple branches off of a basic rod structure, a form called branching filaments
Bacterial arrangements: cocci
- single
- diplococci: pairs
- tetrads: groups of four
- staphylococci or micrococci: irregular clusters
- streptococci: chains
- sarcoma: cubical packet of eight, sixteen, or more cells
Bacterial arrangements: bacilli
- single
- diplobacilli: pair of cells with ends attached
- streptobacilli: chain of several cells
- palisades: cells of a chain remain partially attached by a small hinge region at the ends
Bacterial arrangements: spirilla and spirochetes
- spirilla: occasionally found in short chains
- spirochetes: rarely remain attached after cell division
External structures
Appendages:
- motility: flagella and axial filaments
- attachment points or channels: fimbriae, pili, and nanotubes/nanowires
- flagellum: primary function is motility
Three distinct parts: filament, hook (sheath), basal body
Polar arrangement
Flagella attached at one or both ends of the cell
Monotrichous
Lophotrichous
Amphitrichous
Peritrichous
Monotrichous - single flagellum
Lophotrichous - small bunches or tufts of flagella emerging from the same site
Amphitrichous - flagella at both poles of the cell
Peritrichous - flagella are dispersed randomly over the surface of the cell
Fine points of flagella function
Chemotaxis
Chemotaxis: movement of bacteria in response to chemical signals
- positive Chemotaxis: movement toward favorable chemical stimulus
- negative Chemotaxis: movement away from a repellant
- Run: rotation of flagellum counterclockwise, resulting in a smooth linear direction
- tumble: reversal of the direction of the flagellum, causing the cell to stop and change course
Appendages for attachment or channel formation: fimbriae
Fimbria/fimbriae:
- small, bristle-like fibers sprouting off the surface of many bacterial cells
- allow tight adhesion between fimbriae and epithelial cells, allowing bacteria to colonize and infect host tissues
Appendages for attachment of channel formation: pili and nanotubes
Pilus/pili:
- used in conjugation between bacterial cells
- well characterized in gram-negative bacteria
- type IV pilus can transfer genetic material, act like fimbriae and assist in attachment, and act like flagella and make a bacterium motile
Nanotubes (nanowires):
- very thing, long, tubular extensions of the cytoplasmic membrane
- used as channel to transfer amino acids or to harvest energy by shuttling electrons to iron-rich substances (“breathing rock instead of oxygen”)
S layer
- single layers of thousands of copies of a single protein linked together like tiny chain link fences
- only produced when bacteria are in a hostile environment
glycocalyx
- coating of repeating polysaccharides or glycoprotein units
- slime layer: loose, protects against loss of water and nutrients
- capsule: more tightly bound, denser, and thicker; produce a sticky (mucous) character to colonies on agar
Specialized functions of the glycocalyx
Capsules:
- formed by many pathogenic bacteria
- have greater disease-cause in abilities
- protect against host white blood cells called phagocytes
Biofilms: when the cells divide, they form a dense mat bound together by sticky extracellular deposits around themselves
- plaque on teeth protects bacteria from becoming dislodged
- responsible for persistent colonization of plastic catheters, IUDs, metal pacemakers, and other implanted medical devices
Which of the following bacterial appendages is not used for attachment?
Slime layer
Flagellum
Pilus
Fimbriae
The cell envelope
- it lies outside the cytoplasm
- it is composed of two or three basic layers that each perform a distinct function, but together act as a single protective unit
Three parts of the cell envelop
- cell wall: it determines the shape of the bacterium, the keeping of the strong structural support the cell needs for homeostasis
- cytoplasmic membrane: it provides a site for functions such as energy reactions, nutrient processions, and synthesis. (The major function to regulate transport
- outer membrane (in some bacteria): similar in composition to most membranes, except that it contains specialized types of polysaccharides and proteins
The cell wall
- helps determine the shape of the bacterium
- provides strong structural support to keep the bacterium form bursting or collapsing because of changes in osmotic pressure
- certain drugs target the cell wall, disrupting its integrity and causing lysis (disintegration or rupture) of the cell - gains its relative rigidity from peptidoglycan
Peptidoglycan
Peptidoglycan: one special class of compounds in which polysaccharides are linked to peptide fragments
- polymer of a repeating disaccharides in rows:
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
- provides a strong but flexible support framework
Gram-positive cell wall
- a thick, homogenous sheet of peptidoglycan
- 20 to 80 nm thickness
Contains technical acid and lipoteichoic acid: - function in the cell wall maintenance and enlargement
- contribute to the acidic charge on the cell surface
Define:
Teichoic and lipoteichoic
Teichoic - a polymer of nitros or glycerol (alcohols) and phosphate that is embedded in the peptidoglycan matrix
Lipoteichoic - similar in structure to Teichoic acid but is attached to lipids in the cytoplasmic membrane
Gram-negative cell wall
- a single, thin sheet of peptidoglycan
1 to 3 nm in thickness - thinness gives gram-negative cells more susceptibility to lysis
- acts as a somewhat rigid protective structure as previously described, its thin appearance causes its gram-negative bacteria to be more susceptible to lysis
Gram-Negative cell walls (G-)
- has thin peptidoglycan
- has an outer membrane
- periplasmic space
Comparative characteristics of Gram-positive and Gram-negative bacteria
- crystal violet-iodine crystals from inside the cell
Gram positive- alcohol dehydrates peptidoglycan
- CV-I crystals do not leave
Gram negative - alcohol dissolves outer membrane and leaves holes in peptidoglycan
- CV-I washes out; cells are colorless
- safranin added to stain cells
Nontypical cells walls: acid-fast bacteria
- mycobacterium and norcardia: contain peptidoglycan and stain gram-positive, but bulk of cell wall is composed of unique lipids
Mycolic acid
- very-long-chain fatty acid
- found in the cell walls of acid-fast bacteria
- contributes to the pathogenicity of the bacteria
- makes bacteria highly resistant to certain chemicals and dyes
Nontypical cell walls: Archaea
- exhibit unusual and chemically distinct cell walls
- some have cell walls composed entirely of polysaccharides
- other have cell walls made of pure protein
- all lack true peptidoglycan structure
- some lack a cell wall entirely
Mycoplasms and other cell-wall-deficient bacteria
Mycoplasmas:
- naturally lack a cell wall
- sterols in the cell membrane stabilize the cell against lysis
- Mycoplasma pneumoniae: “walking pneumonia”
L forms:
- some bacteria that naturally have a cell wall but lose it during a part of their life cycle
- role in persistent infections
- resistant to antibiotics
The gram negative outer membrane
- similar in composition to most membranes, except it contains specialized polysaccharides and proteins
Lipopolysaccharide: is a macromolecule; signaling molecules and receptors; endotoxin
Porin proteins: they completely span the outer membrane; special membrane channels that only the outer membrane allows certain chemicals to penetrates
Cytoplasmic membrane structure
- a lipid bilayer with proteins embedded
Serves as a site for: energy reactions, nutrient processing, synthesis, and regulates transport of nutrients and wastes
Selectively permeable: special carrier mechanisms for passage of most molecules
Differences in cell envelop structure
- outer membrane of gram-negative bacteria contributes and extra barrier:
- resistant tot certain antimicrobial chemicals
- more difficult to inhibit or kill than gram-positive bacteria
Alcohol-based compounds dissolve lipids in the outer membrane and therefore damage the cell:
- alcohol swabs used to cleanse the skin before certain medical procedures
Treatment of infections is caused by gram-negative bacteria and requires drugs that can cross the outer membrane
Structures internal to the cell wall
The plasma (cytoplasmic) membrane
- phospholipid bilayer that encloses the cytoplasm
- peripheral proteins on the membrane surface
- internal and transmembrane proteins penetrate the membrane
Bacterial chromosomes and plasmids
- the hereditary material of most bacteria exists in the bacterial chromosomes
- DNA is aggregated in the nucleotides
Plasmids: nonessential pieces of DNA; confer protective traits such as drug resistance and toxin and enzyme production
Ribosomes
- site of protein synthesis
- composed of rRNA (60%) and protein (40&)
Consists of a large and small subunit:- small subunit: 30S
- large subunit: 50S
- large and small subunits together: 70S
- archaeal ribosome: 70S
- eukaryotic ribosome: 80S
Inclusion bodies and microcompartments
- used for food storage
- pack gas into vesicles for bouyancy
- store crystals of iron oxide with magnetic properties
Bacterial microcompartments:- outer shells made of protein, arranged geometrically
- packed full enzymes designed to work together in biochemical pathways
The cytoskeleton
- som bacteria produce long polymers of protein similar to eukaryotic cells for the cytoskeleton:
- arranged in helical ribbons around the cell
- contribute to cell shape
- have also been identified in archaea
- unique to non-eukaryotic cells -> may be a potential target for antibiotic development
Maturation and release of enveloped viruses
- dormant bodies
- produced by Bacillus, clostridium, and sporosarcina
- vegetative cell: metabolically active
- sporulation: induced by environmental conditions
- endospores resist extremes of heat, drying, freezing, radiation, and chemicals that would kill vegetative cells
The medical significance of bacterial endospores
Bacillus anthracis: agent of anthrax
Clostridium tetani: cause of tetanus
Clostridium perfringens: cause of gas gangrene
Clostridium botulinum: cause of botulism
Clostridioides difficile: “C. Diff,” a serious gastrointestinal disease
Archaea
- a third cell type in a separate superkingdom
- more closely related to domain eukarya than bacteria:
- Share rRNA sequences not found in bacteria
- Protein synthesis and ribosomal subunit structures are similar
Archaea differ from other cell types:
Have entirely unique sequences in rRNA
Exhibit a novel method of DNA compaction
Contain unique membrane lipids, cell wall compartments, and pilin proteins
Extremophiles: come life at extremely high or low temperatures, some need extremely high salt or acid concentrations to survive, some live on sulfur or methane, some live on the human body and may be capable of causing human disease
Classification systems for bacteria and archaea
Bergey’s manual of systematic bacteriology:
- comprehensive vie of bacterial and archaeal relatedness
- based on rRNA sequencing
Bergey’s manual of determinative bacteriology:
- based entirely on phenotypic characteristics
- categorizes organisms based on traits command assayed in clinical, teaching, and research labs such as shape as seen in a microscope, or metabolic capabilities (what they need to grow)
Taxonomic scheme
Four major divisions of bacteria and archaea based on the nature of the cell wall:
- gracilicutes: gram-negative with thin cell walls
- firmicutes: gram-positive with thick, strong cell walls
- tenericutes: lack a cell wall and are soft
- mendosicutes: archaea, primitive cells with unusual cell walls and nutritional habits
Species and subspecies in bacteria and archaea
Bacterial species:
- a collection of bacterial cells, all of which share an overall similar pattern of traits
- should share at least 95% of their genes as matches
Subspecies, strain, or type:
- bacteria of the same species that have differing characteristics
Serotype:
- representative of a species that stimulate a distinct pattern of antibody (serum) responses because of unique surface molecules
The three major shapes of bacteria
- coccus
- bacillus
- vibrio
Why is the Gram-positive cell wall considered to be stronger than the Gram-negative cell wall? Your answer should describe the differences between each type of cell (composition, etc) and what makes the G+ cell stronger. This should be more than 3 sentences
A gram-positive cell wall is considered stronger because of the cell wall thickness, but also because the cell wall has a very thick sheet of peptidoglycan. Whereas the gram negative cell wall is weaker because of a much thinner peptidoglycan sheet which is 1 to 3 nm thickness while the gram-positive is 20 to 80nm thick. Not only are these major differences but the chemical reactions when a gram stain is being done are very different. In a gram-positive cell when a gram stain test is done the red dye inserted is masked when the cells violet coloring soaks it up. However, in the gram negative cell when the red dye is inserted during the gram stain test the colorless cell soaks up the red dye due to a thinner wall for the stain to come through. The gram-positive cell is also stronger because its thicker cell wall makes it harder for things like microbes, microorganisms, and even stains to get through. The gram-negative cell however has a much thinner wall providing an easier access point for all pathogens and substances.
What are some of the most important various structures in bacterial cytoplasm
- ribosomes
- chromosome/chromosomes
- plasmids
What is the role of endo spore formation
The primary function of a bacterial endo spore is to ensure the survival of a bacteria during harsh environmental conditions
- it is a dormant body that is produced by various types of bacteria like Bacillus, Clostridium, and even Sporosarcina
Define:
Sporulation
Germination
Sporulation - a strategy utilized by a wide variety of organisms to adapt to changes in their individual environmental niches and to survive in time and/or space until they encounter conditions acceptable for vegetative growth
Germination - the development of a plant from a seed or spore after a period or dormancy
