Bacterial Division, Morphology & cell Components

Bacterial Division and Morphology

• Bacteria divide in half through a process called binary fission.
• Each species and genus has a characteristic morphology.
• Bacterial morphology follows general rules - Shapes remain consistent throughout life, coccus and bacillus are common shapes.
• Arrangement, which is the morphology, depends on the position of offspring cells following fission.
• The "plane of division" is where cell division occurs, typically the cell's shortest plane.
• If all planes are equal in length, then arrangement depends on whether the planes are fixed or random, and the number of possible planes.

Cellular Components and Functions

• All cells reproduce using DNA.
• All cells perform macromolecular synthesis using cytoplasm and ribosomes.
• Cytoplasmic membrane, cell wall (in most), and outer membrane (in some) provide structure and form.
• Cell wall (in most), outer membrane (in some), and glycocalyx (in some) provide protection.
• Cytoplasmic membrane and cytoplasm produce energy.

Cellular Envelope

• The cellular envelope includes all layers separating the cytoplasm from the external environment.
• Gram-positive bacteria have a cell membrane, a thick cell wall, and no outer membrane.
• Gram-negative bacteria have a cell membrane, a thin cell wall, and an outer membrane.
• Acid-fast bacteria have a cell membrane, no outer membrane, and a thick cell wall covered in waxy lipid mycolic acid.

Cellular Membrane

• A cellular membrane is a symmetrical lipid bilayer with embedded proteins.
• Cellular membrane is found in all living things.

Passive and Active Transport

• Passive transport involves movement of materials across the membrane from high to low concentration areas, without requiring energy.
• Two forms of passive transport include simple diffusion and osmosis.
• Active transport is movement of materials across the membrane in any direction and requires energy and transport proteins.
• Transport protein examples include simple transporters, ATP-binding cassette systems (ABC transporter), and group translocation.

Peptidoglycan

• Peptidoglycan is a structure that can be an antibiotic target.
• Beta-lactam antibiotics inhibit tetrapeptide synthesis.
• Vancomycin blocks peptide interbridge formation.
• Some bacteria lack cell walls.
• Outer membranes have a unique asymmetric lipid bilayer consisting of lipopolysaccharide (LPS) instead of phospholipids in the outer leaflet.
• Porins are water-filled size exclusion channels that control access to the periplasm.
• Glycocalyx is found in some, but not all Gram-negative and Gram-positive bacteria.

Glycocalyx

• The two forms of glycocalyx are capsule, which is medically relevant and regular, and slime layer, which is common in environmental organisms and diffuse/irregular.
• The capsule and slime layer provide protection and attachment.

Flagella

• Flagella are long, hollow protein structures, thin and whip-like, that help bacterial cells move and are found in some, but not all Gram-negative and Gram-positive bacteria.
• Flagella enable motility can rotate more than 100,000 revolutions per minute, facilitating "run and tumble" movement.
• Flagella are powered by proton motive force.
• The three basic parts of the flagella are the filament, hook, and basal body.
• Flagella enable chemotaxis, magnetotaxis, phototaxis, aerotaxis, and thermotaxis by sensing the environment.

Pili

• Pili are considerably shorter and thinner than flagella, and have a hollow structure comprised of pilin monomers.
• Pili enable attachment, virulence, twitching motility, gliding motility, and conjugation (sex pili, F pili).

Internal Structures

• In the cytoplasm, prokaryotic cells have various internal structures.
• Chromosomes and ribosomes are essential structures for life in the cytoplasm.
• Plasmids, storage granules, and endospores are optional components that may provide a selective advantage.
• A nucleoid is a region in the cytoplasm where the cell's DNA is stored, but it is not an enclosed organelle.
• Supercoiling involves two strands of DNA twisted around themselves (condenses DNA).
• Nucleoproteins facilitate additional compaction of DNA volume.
• Chromosomes contain genetic information (DNA encodes all essential functions).
• Ribosomes are the site of protein synthesis and composed of large and small subunits made of ribonucleoproteins and rRNA.
• Ribosomal subunits are small (30S) and large (50S), totaling 70S when assembled on mRNA.
• Plasmids are supercoiled double-stranded DNA that replicate independently of the cell chromosome and are often present in multiple copies.
• Plasmids contain "accessory" genes that confer selective advantages.
• Two medically important plasmid varieties are R factors, which encode antibiotic resistance factors, and F factors, which encode conjugation systems.
• Endospores are dormant cells of medically relevant bacteria like Bacillus, Clostridium, and Clostridiodes.
• Endospores are produced by sporulation, a process where cells form specialized spores to survive harsh conditions.
• Endospores are resistant to heat, desiccation, chemicals, and UV light.

Clostridium

• A vegetative cell is produced by germination.
• Clostridium botulinum is a Gram-positive, obligately anaerobic, spore-forming bacillus.
• Clostridium botulinum causes botulism, primarily an intoxication with symptoms resulting from botulinum toxin activity.
• Clostridium botulinum infection has variants of GI and wound infections.
• Clostridium botulinum is found in soils worldwide and is typed by the allele of the botulinum toxin gene, with type A being the most significant.
• Within 12-36 hours after consuming contaminated food, signs and symptoms of Clostridium botulinum occur after consuming contaminated food(intoxication form)
• Clostridium botulinum causes descending flaccid paralysis of muscles, dipolia.
• Symptoms of Clostridium botulinum include pain, nausea, emesis (vomiting), and/or diarrhea followed by blurred vision.
• Untreated Clostridium botulinum can lead to respiratory paralysis and death.
• Treatments and prevention for Clostridium botulinum include antitoxin antibodies, enemas (GI), and surgical debridement (wound).
• Clostridium tetani is a Gram-positive, obligately anaerobic, spore-forming bacillus.
• Clostridium tetani causes tetanus, an infection with symptoms resulting from tetanospasmin toxin activity.
• There are 3 forms of Clostridium tetani: traumatic injury (most common), GI tract, and neonatal.
• Clostridium tetani is found in soils worldwide and is usually associated with piercing injuries by contaminated objects.
• Clostridium tetani symptoms include muscle spasms-tetany, trismus "lockjaw," and opisthotonos (severe hyperextension and spasticity).
• Untreated Clostridium tetani can lead to death by aspiration pneumonia.
• Treatments and prevention of Clostridium tetani include neutralizing antitoxin antibodies, debridement, muscle relaxers, and supportive care.
• Clostridium perfingens is a Gram-positive, obligately anaerobic, spore-forming bacillus.
• Clostridium perfingens causes clostridial myonecrosis (gas gangrene) resulting from alpha toxin and exoenzyme activity and Clostridium perfingens food poisoning resulting from Clostridium perfingens enterotoxin (CPE) activity, usually due to poor food handling, preparation, and storage.
• Clostridium perfingens is found in soils worldwide and is typed by the toxin gene possessed, with type A being the most significant.
• Symptoms of clostridial myonecrosis from Clostridium perfingens includes a long delay in treatment after a traumatic injury, alpha toxin kills white blood cells and hyaluronidase/collagenase destroy tissue, edema and tissue necrosis lead to frothy exudate, excruciating pain, and delirium.
• Untreated Clostridial myonecrosis can lead to death due to organ failure.
• Symptoms of Clostridium perfingens food poisoning (CFP) include: spores survive cooking and germinate in large intestine due to anaerobic conditions causing abdominal pain, emesis, diarrhea, and nausea.
• Treatments for clostridium perfingens includes antibiotics, debridement, hyperbaric oxygen chamber, and IV fluids.

Clostridioides difficile

• Clostridioides difficile is a gram positive, obligately anaerobic, spore-forming bacillus.
• Clostridioides difficile causes antibiotic-associated pseudomembranous colitis, an infection with symptoms resulting from toxin A (TcdA) and toxin B (TcdB) activity.
• Clostridioides difficile is found in soils worldwide and in the colons of 5% of humans.
• Clostridioides difficile is a consequence of extended time on standard or high-dose regimens of antibiotics.
• Nosocomial transmission is common, with up to 30% of hospitalized patients carrying Clostridioides difficile.
• Antibiotics eliminate normal flora, leading to C. difficile overgrowth.
• Symptoms of Clostridioides difficile include antibiotic-associated pseudomembranous colitis, TcdA/B kills intestinal epithelia causing peeling, neutrophil and bacteria fill the gap to form painful pseudomembrane, edema can lead to mild to severe diarrhea.
• Treatments and prevention for Clostridioides difficile include antibiotic removal/substitution, narrow spectrum antibiotic usage, and fecal transplant.

Bacillus

• Bacillus anthracis is a Gram-positive, obligately aerobic, spore-forming bacillus.
• Bacillus anthracis causes anthrax, an infection with symptoms resulting from anthrax toxin activity.
• Bacillus anthracis is found in soils worldwide.
• Anthrax comes in three forms: cutaneous, gastrointestinal, and inhalation, all three forms depend on anthrax toxin (A-B type toxin).
• Anthrax toxin contains Two "A" subunits - lethal factor (cell death) and edema factor (tissue swelling) and B subunit - receptor binding (protective antigen).
• Cutaneous anthrax produces black necrotic eschar.
• Gastrointestinal anthrax symptoms include nausea, vomiting blood, abdominal pain, and severe diarrhea.
• Inhalation anthrax symptoms include influenza-like symptoms that progress to lung bleeds and bloody cough -> meningitis, septic shock commonly followed by death.
• Treatments and prevention for Bacillus anthracis include antibiotics and vaccines.
• Bacillus cereus is a Gram-positive, obligately aerobic, spore-forming bacillus.
• Bacillus cereus causes Bacillus cereus food poisoning, usually an intoxication with symptoms resulting from anthrax-toxin activity.
• Extreme contamination of Bacillus Cereus can lead to an infection of the small intestine due to high oxygen levels.
• Bacillus cereus is found in soils worldwide and their spores survive cooking (usually a result of poor food handling/preparation).
• Bacillus cereus intoxication symptoms depend on emetic toxin (toxin survives stomach acid causing vomiting due to stimulation of vagus nerve).
• Bacillus cereus infection symptoms depend on several enterotoxins which trigger perforations in intestinal cells (toxin not acid-stable) and spores germinate in small intestine and secrete enterotoxins leading to watery diarrhea.
• Treatments and prevention for Bacillus cereus include fluids.

Drug Targets and Eukaryotic Morphology

• Understanding what a particular drug interferes with, requires knowing what the drug targets.
• Selective toxicity depends on whether the drug target is present in humans and if the drug will interfere with our physiology.
• Eukaryotic morphology showcases a wide array of forms and shapes of cells adapted to specific environments.
• Cytoskeletal structures allow remodeling of cell shape for many eukaryotes.
• Eukaryotes can transition between morphological forms during their lifetime.
• Trophozoite is a general term for vegetative, metabolically active cell types.
• Cyst is a general term for dormant, metabolically inactive cell types.
• Eukaryotic arrangement: Eukaryotes may divide in half by binary fission or rely on mitosis (may produce spores during replication, fungi, algae).
• Eukaryotic plane of division: Eukaryotes devide along the shortest axis.
• Eukaryotes can be unicellular (organisms consisting of a single cell) and multicellular (organisms composed of multiple cells) and Dimorphic (exist in 2 forms).
• Basic cellular eukaryote functions: shapes must support basic cellular functions.
• Eukaryote reproduction: DNA
• Eukaryote macromolecular synthesis: Cytoplasm, Endoplasmic Reticulum, Ribosomes
• Eukaryote Structure and form: Cytoplasmic membrane, Cell wall (some), Cytoskeleton
• Protention in Eukaryotes: Cell wall (some), Cytoskeleton
• Energy production in Eukaryotes: Mitochondria, Chloroplast, Cytoplasm (all)
• Eukaryote plasma membrane: The plasma membrane has similar chemical structure and function to the bacterial cytoplasmic membrane
• Important differences of the Eukaryotic plasma membrane: Asymmetric composition, membrane commonly contains sterols for strength

Eukaryotic Cell Features

• Animal cells contain cholesterol.
• Fungal cells contain ergosterol.
• Eukaryotic passive transport: Eukaryotic cells uses diffusion and osmosis, has channel and carrier proteins, it permits facilitated diffusion, moves across membrane exploiting a concentration gradient(system can only eliminate concentration gradient) and energy is not used.
• Active transport eukaryotes: transport proteins-energy dependent
• Bulk transport, unique to eukaryotes, requires mechanical movement of lipid bilayer membranes.
• Endocytosis refers to inward movement toward the cytoplasm.
• Exocytosis refers to outward movement toward the environment.
• Cell wall function in plant cells: prevents osmotic lysis and provides protection.
• Fungi contain chitin and gluons in cell wall.
• Algae contain cellulose and pectin in cell wall.
• Flagella in eukaryotes are comprised of 9 pairs of microtubules around 2 central individuals that plasma membrane surrounds and dyein protein hydrolyzes ATP to power movement
• Cillia in eukaryotes: unique to eukaryotes, simailar to eukaryotic flagella but shorter, it often covers the cell and can move or propel surrounding along stationary cell
• Cytoskeleton provides structure and protection.
• The thickest structure in cytoskeleton: microtubules- long hollow cylinders made of protein subunits called tubulin
• Actin filaments: comprised of actin monomers which rapidly assemble/disassemble, has pseudopod formation
• The intermediate fibers function to strengthen the cell, enabling cell to resist physical stress.
• Eukaryotic organelles are membrane-bound and possess more than 1 one lipid bilayer (4 most common are nucleus, Golgi apparatus, ER, and mitochondria).
• The ER in eukaryotes is a synthetic center for biological macromolecules.
• Smooth ER primary regions of ER include lipid synthesis/degradation and Ca2+ storage
• Rough ER (Granular appearance)primary regions of ER include ribosome attachment and protein synthesis.
• Mitochondria in eukaryotes: Energy-producing organelle with a dual lipid bilayer membrane, the inner membrane form crista and is the site of ATP Synthase, Electron Transport Chain.
• Matrix in Eukaryotes: The matrix is similar to prokaryotic cytoplasm, inside of inner membrane, DNA encodes mitochondrial proteins, replication factors and Ribosomes - 70S, not 80S.
• Chloroplast in eukaryotes: are Energy producing organelle. The organnelle has a dual lipid bilayer membrane, the Inner membrane form thylakoids, its the site of reaction center complexes, chlorophyll and permits capture of light energy for photosynthesis.
• Stroma in Chloroplast: The stroma is similar to prokaryotic cytoplasm, its inside of inner membrane. DNA encodes mitochondrial proteins, replication factors and Ribosomes - 70S, not 80S.
• Endosymbiotic theory: ancestors of mitochondria and chloroplasts were bacteria.
• Accidental mutualism: over time, both lost genes encoding biochemical activities that the other provided and now are inseparable.

Evidence for the Endosymbiotic Theory

• Mitochondria/chloroplast DNA encodes 70S ribosomes.
• Double membranes surround Mitochondria/chloroplast.
• Mitochondria/chloroplast divide by binary fission, not mitosis.
• Mitochondria DNA is highly similar to intracellular parasites (genus Rickettsiae).
• Chloroplast DNA is highly similar to photosynthetic bacteria (phylum Cyanobacteria).