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Morphology of bacterial cells
-Bacteria can take many different shapes (or morphologies).
-Spherical (s. coccus, pl. cocci)
-Rod-shaped (s. bacillus, pl. bacilli)
-Comma-shaped (s. vibrio, pl. vibrios)
-Spiral (s. spirillum, pl. spirilla)
-Pleiomorphic (varied shapes)- no cell wall so they can take many forms
-No membrane bound organelles
Some can grow in complex multicellular arrangements
-Hyphae (branching filaments of cells)
-Mycelia (tufts of hyphae)
-Trichomes (smooth, unbranched chains of cells)
What advantages might a microbial species that forms multiples arraignments (clusters or chains) have that are not afforded unicellular microbes
-Those at the center of the community are not exposed as much as they microbes at the side of communities so enables the community to survive
-Can share nutrients and metabolic products (especially in hospitable conditions)
Sizes of bacteria
-Usually smaller than eukaryal cells (bacteria are often 0.5‒5 μm in length)
-SMALL eukaryal cells are usually >5 μm in diameter
Exceptions to size
-Thiomargarita namibiensis: up to 700 μm in diameter!
-Epulopiscium fishelsoni: 200‒700 μm x 80 μm!
-Some mycoplasma cells are only 0.2 μm in diameter.
-Large size helps deter predation
What causes a species to have a particular size or shape?
-Surface area to volume ratio
-The great the ratio, the more efficient you are to taking up nutrients or avoiding toxins
-Rod shaped cells have a higher surface area and are able to pick up nutrients more efficiently
Size Shape relationship
-As the S/V ratio increases, nutrient uptake and diffusion of molecules become more efficient
-surface to volume ratio (S/V)
-large size may be protective mechanism from predation
-Rod-shaped cells have a higher S/V than coccus shape so greater nutrient flux across the membrane
-More surface area = more room to take things in from the environment and release things (rid of such as toxins) things to environment
Cytoplasm of Bacterial cell
-Largest area is the nucleoid region, housing the chromosomes and DNA replication machinery
-One single, circular piece of DNA that is super coiled
-irregularly shaped region in bacteria and archaea
-usually not membrane bound (few exceptions)
-location of chromosome and associated proteins
(a single closed circular, double-stranded DNA molecule )
-supercoiling - produces a dense central core with loops
-and nucleoid proteins (HU) probably aid in folding
-Small, single closed circles
-extrachromosomal DNA; found in bacteria, archaea, some fungi
and usually small, closed circular DNA molecules
-exist and replicate independently (self replicating) of chromosome
-episomes - plasmids that can integrate into the cell chromosome
-contain few genes that are non-essential
(confer selective advantage to host (e.g., drug resistance))
-may exist in many copies in cell
-inherited stably during cell division
-Sometimes plasmids can be loss during cell division - called curing
-classification of plasmids based on mode of existence, spread, and function
-Floating in cytoplasm!
consisting of protein and RNA ; sites of protein synthesis
-bacterial and archaea ribosome = 70S
- S = Svedburg unit
-bacterial and archaeal ribosomal RNA
-16S rRNA and SSU proteins - small subunit = 30S
-23S rRNA, 5S rRNA and LSU proteins - large subunit = 50S
-archaea have additional 5.8S in large subunit (also seen in eukaryotic large subunit)
-proteins vary: archaea more similar to eukarya than to bacteria
Remainder of Cytoplasm of bacterial cells
-The remainder of the cytoplasm is a stew of macromolecules (tRNA, rRNA, mRNA, proteins, etc.).
-Inclusion bodies (many for storage) may also be present:
-Polyhydroxybutyrate granules - carbon storage
-Sulfur globules - sulfur storage
-Gas vesicles - buoyancy control
-Carboxysomes - location of carbon fixation reactions
-Magnetosomes - organelles associated with direction finding
-Common in all cells
-granules of organic or inorganic material that are stockpiled by the cell for future use
-some are enclosed by a single-layered membrane
-membranes vary in composition
-some made of proteins; others contain lipids
-may be referred to as microcompartments
-storage of nutrients, metabolic end products, energy, building blocks
-phosphate storage - polyphosphate (Volutin or metachromatic granules)
-amino acids - cyanophycin granules- large peptides not coded by mRNA
Other inclusions - Gas vacuoles
-found in aquatic, photosynthetic bacteria and archaea
-provide buoyancy in gas vesicles
-Aggregates of small, hollow, cylindrical gas vesicles
Other inclusions - Magnetosomes
-found in aquatic bacteria; have to be mobile
-Little magnets with iron oxide granules that make it magnetic - aligns self with magnetic field (have to be in a line)
-magnetite particles (Fe3O4) for orientation in Earth's magnetic field-swim toward nutrient-rich sediments
-cytoskeletal protein MamK (hold them in a line so they can be magnetic)
helps form magnetosome chain
-What kinds of internal structures help to organize bacterial cells?
-The cytoskeleton is a series of internal proteins that assist in keeping everything in (or moving it to) the right locations in cells.
-Some cytoskeleton proteins are involved in cell wall synthesis during cell division (FtsZ and MreB)
-Other cytoskeleton proteins are involved in moving internal items
-Responsible for cell division and laying down Z line in the center of the cell
-Observed in bacteria and archaea
-Induces curvature in curved rods
During protein synthesis what molecules become associated with the ribosomes
-mRNA and tRNA
How do plasmids differ from bacterial chromosomes?
-plasmids are just small pieces that are not essential
-But, their shape (single circular) is the same, they both self replicated
The cell membrane
-ALL cells have a plasma membrane (PM).
-Separates the interior of the cell from the external environment
-Usually composed of a phospholipid bilayer with embedded proteins
Bacterial plasma membrane
-Important interface between inside and outside
-absolute requirement for all living organisms (viruses don't have them)
-some bacteria also have internal membrane systems
Plasma membrane functions
-encompasses the cytoplasm
-selectively permeable barrier
-interacts with external environment
-receptors for detection of and response to chemicals in surroundings
-transport systems (electron transport system which involves a membrane)
-Membranes are lipid bilayers with floating proteins
-amphipathic lipids - asymmetric
-polar ends (hydrophilic - interact with water)
-non-polar tails (hydrophobic - insoluble in water- are located inside)
Membrane Proteins: Peripheral
-loosely connected to membrane
-Make up 20 - 30% of membrane proteins
Membrane proteins: Intergal (inside membrane)
-amphipathic - embedded within membrane, not easily extracted
-Carbohydrates often attached
-carry out important functions (transport, energy ETS)
-Can move laterally in the membrane
-may exist as microdomains (patchwork)
-Very dynamic - saturation levels of membrane lipids reflect the environmental conditions such as temperature
-bacterial membranes lack sterols but do contain sterol-like molecules, hopanoids;
stabilize membrane and
found in petroleum
Why might bacterial plasma membranes carry out more activities than eukaryotic membranes?
-It's the only membrane that they have - a lot of cell actives are carried out in membranes so they have to make full use of it.
The cell membrane
How do items cross the PM and get into a cell?
-O2 and CO2 are small and can diffuse across readily.
-H2O is helped across by aquaporin protein channels.
-Osmosis is the flow of water across the PM toward the side with a higher solute (particle) concentration.
-Osmosis can cause a cell to swell with water or shrivel as water leaves, but a strong cell wall can help keep a bacterial cell alive during these hardships.
How do organisms take up nutrients?
-microbes can only take in dissolved particles across a selectively permeable membrane which prevents free passage of unwanted materials. (MUST HAVE DISSOLVED NUTRIENTS)
-Must be able to take up specific molecules not substances that they don't need (SELECTIVE)
-Must concentrate against a gradient if living in an environment with very low concentrations of nutrients (THIS IS ENERGY INTENSIVE)
-microorganisms have developed a number of different transport mechanisms to accomplish this (oxygen and carbon dioxide don't require any mechanisms they pass freely)
-facilitated diffusion - all microorganisms
-active transport - all microorganisms
-group translocation - Bacteria and Archaea
-endocytosis - Eukarya only
-Can only go from a region of higher concentration to a region of lower concentration
-Not energy dependent
-The rate of diffusion depends on the concentration gradient - conc. must be higher outside than inside
Larger gradient = faster rate
-H2O (allows cells to adjust to ionic concentrations), O2, and CO2 often move across membranes this way - larger molecules enter by other mechanisms
-similar to passive diffusion
-movement of molecules is not energy dependent
-direction of movement is from high concentration to low concentration (no energy required)
-size of concentration gradient impacts rate of uptake
-differs from passive diffusion :
-uses membrane bound specific carrier molecules (permease proteins embedded in the cell membrane) which greatly increases the rate of diffusion
-smaller concentration gradient is required for significant uptake of molecules
-effectively transports glycerol, sugars, and amino acids
-more prominent in eukaryotic cells than in bacteria or archaea
-Rate of facilitated diffusion increases more rapidly and at a lower concentration
-Diffusion rate reaches plateau when a carrier becomes saturated (plateau is genetically predetermine i.e.number of molecules allowed in the plasma membrane)
Facilitated Diffusion Summary
-No energy required
-A concentration gradient spanning the membrane drives the movement of molecules
-Is reversible depending on conc of molecules
-The gradient can be maintained by transforming the transported nutrient into another compound
-Not useful to bacteria and Archaea that live in environments with low conc of nutrients
-ATP or proton motive force used
move molecules against a gradient (ie., from low conc to high conc)
-concentrates molecules inside cell
-involves specific carrier proteins (permeases)
-carrier saturation effect is observed at high solute concentrations
Primary Active Transport
Primary Active Transporters (ABC Transporters) - use energy provided by ATP hydrolysis to move substances against a conc gradient
-primary active transporters use ATP
-ATP-binding cassette transporters
-observed in Bacteria, Archaea, and eukaryotes
-Consist of :2 hydrophobic membrane spanning transporter proteins,
2 cytoplasmic associated ATP-binding domains,Solute binding proteins in periplasmic space of Gram negative organisms or attached to membrane lipids of the plasma membrane of Gram positive organisms - used to interact with the transporter proteins
-Considered to be uniport - transports one molecule at a time
Secondary Active Tranport
Secondary Active transporters (MFS Transporters) - couple the potential energy of ion gradients to transport substances
-major facilitator superfamily (MFS)
-uses ion gradients to co-transport substances
-e.g., transport of lactose using lactose permease in E. coli - transports lactose and a proton simultaneously into the cell - considered symport - two substances both move in the same direction
-e.g., transport of sugars and amino acids in E. coli while pumping sodium out - considered antiport - two substances move in opposite directions
Why might an organism have more than one uptake system for certain substances?
-If they require a lot of one substrate
-If there is a mutation, a toxin, or something happens and one mechanism can no longer function; multiple uptake systems will ensure that the cell lives in this case and has a back up system
Phosphotransferase system (PTS)
-PEP (high energy, like ATP) + Sugar (outside) -> pyruvate + Sugar-phosphate (inside)
-Example of a phosphorelay system
-Found in many facultatively anaerobic bacteria and in some obligate anaerobes but not found in aerobes
-Also involved in chemotaxis
Iron uptake - special case of active transport
-microorganisms require iron
-ferric iron is very insoluble so uptake is difficult
-microorganisms secrete siderophores to aid uptake
-siderophore complexes with ferric ion
-complex is then transported into cell
-Protein secretion and the PM: making proteins and shipping them outside the cell
-Uses ATP energy!
-Toxins, siderophores, enzymes, etc.
-Sec system responsible for transporting proteins through the cell membrane
Sec system takes unfolded proteins and passes them through to outside environ
Type 3 system:Injectozone system
-Type 4 system: Congungation system
Bacterial cell wall
-peptidoglycan (murein): rigid structure that lies just outside the cell membrane
-Site of action of several antibiotics (e.g., penicillin)
-two types based on Gram stain
-gram positive - stain purple; single thick peptidoglycan
-gram negative - stain pink or red; thin peptidoglycan with an outer membrane and a periplasmic space
Functions: maintains shape of the bacterium (almost all bacteria have one),
helps protect cell from osmotic lysis,
helps protect from toxic materials,
may contribute to pathogenicity
Peptidoglycan Structure of Cell wall
-meshlike polymer of identical subunits forming long strands
-two alternating sugars:N-acetylglucosamine (NAG) and N- acetylmuramic acid (NAM)
-And four alternating D- and L- amino acids (D amino acids not found in proteins, thought to protect against degradation by peptidases)
-Each peptidoglycan disaccharide subunit is: N-acetylmuramic acid (NAM) with a small peptide chain
(The peptide varies by species.) and N-acetylglucosamine (NAG)
-While the amino acids in the peptide on NAM can vary from species to species, the way the peptides are crosslinked in the CW can also vary.
-Several of the amino acids found associated with NAM in peptidoglycan are unusual D forms.
-D forms are stereoisomers (mirror images) of the L forms normally found in biological proteins.
How does the CW (cell wall) form?
-NAM is synthesized in the cytoplasm and linked to UDP
-NAM is linked to bactoprenol
-NAG is added to NAM
-Bactoprenol flips NAM-NAG to periplasm
-Disaccharide added to existing chain, Crosslinking of chains also occurs
-Bactoprenol flips back to cytoplasm
-THE CW STRUCURE CAN BE DEGRADED (naturally by lysostatin secretions and artificially by B-lactam antibiotics (work by preventing peptidoglycan cross linking, weakening the cell wall structure))
-When you weaken the CW the cell can't resist the osmotic pressure changes and will die
-not all cell wall structures are the same (gram stains used to separate microbes into 2 classes - read toolbox 2.1)
Gram positive cells envelope
A thick outer layer of peptidoglycan
A very narrow periplasmic space
Teichoic acids in the peptidoglycan (negatively charged)
A varying width periplasmic space containing a very thin layer of peptidoglycan
An outer membrane composed of lipopolysaccharide (LPS)
consists of three parts: lipid A, core polysaccharide, O side chain (O antigen)
-lipid A embedded in outer membrane
-core polysaccharide and O side chain extend out from the cell
-LPS from Gram-negative cells can be harmful!
-Lipid A portion induces a strong inflammatory response (breathing it can make you sick but if a gram negative cell (LPS) is present in an IV fluid, a person will die within a few minutes because body systems close down in response to this molecule (endotoxin)) NO TREATMENT
-O (outer) side chain of polysaccharides can vary dramatically (and even be changed by the microbe to evade host immune responses
Importance of LPS
-contributes to negative charge on cell surface
-helps stabilize outer membrane structure
-may contribute to attachment to surfaces and biofilm formation
-creates a permeability barrier - restricts entry of bile salts, antibiotics, and other toxic substances
-protection from host defenses (O antigen - elicits an immune response from the infected host)
-can act as an endotoxin (lipid A-may elicit septic shock- no treatment)
Gram-neg outer membrane permeability
-more permeable than plasma membrane due to presence of porin proteins and transporter proteins
-porin proteins form channels through which small molecules (600-700 daltons) can pass
-responsible for transporting water molecules to get through outer membrane of gram neg cells
Why is this true? Yellow OF medium color means carb catabolism has taken place and Blue OF medium color means peptone catabolism has taken place.
One reason food is refrigerated to control microbial growth is because irreversible cell damage is more likely to occur at low rather than high temperatures.
How does the Poliovirus enter the human body?
For what is MSA selective and differential?
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