Bacterial Structure – Flashcards
Unlock all answers in this set
Unlock answers
Bacteria vs Archaea |
-Common Ancestor -Bacteria -Gram positive/negative -Spirochetes -Chlamydia -Archaea (formerly called archaebacteria) -No known pathogens (yet) -Contains many extremophiles Methanogens (obligate anaerobes) swamps, anaerobic ground water sources: Carbon derived from carbon dioxide or acetate Extreme halophiles: Require high salt (3-5 M) Extreme thermophiles: 55-100ºC Some species present in digestive tract Biochemically distinct from bacteria No peptidoglycan -Membrane chemistry different |
Typical bacterial diameter |
-0.5 mm to 1 mm |
Colony Appearance |
-Colony consistency and texture -Dry, slimy (mucoid), buttery -Smooth surface, wet, rough, granular -Opaqueness Pigment -None(usually pathogen's color), red, yellow, orange, brown, green |
; ; ; Relationship Between Colony Appearance and Cell Physiology |
Colony appearance may give important clues about the identity of the organism -Colony morphology does NOT relate to shape of individual bacteria -Mucoid appearance often indicates capsule -Waxy appearance indicates high lipid content- could be Mycobacterium -Highly motile organisms often form thin, spread-out colonies -Pigments are often a form of protection against light- indicates where organism normally lives |
Cell Envelope
|
Definition :Consists of cell membrane(s), cell wall (if present), including imbedded proteins, and glycocalyx or capsule (if present) Functions: Barrier -Osmotic protection -Regulated environment (pH, solute gradients)
-Solute transport -Electron Transport -Electrochemical gradients/ATP synthesis -Motility -Lipid biosynthesis -Protein Secretion |
Gram Positive Cell Envelope |
-Thickpeptidoglycan layer -Teichoic and lipoteichoic acids -Give cell wall a net negative charge -Important for serotyping -Can be shed and elicit host immune response |
Gram Negative Cell Envelope |
Outer membrane limits access of penicillin -Thin peptidoglycan layer - Two Membranes -Periplasmic space: May contain virulence factors such as collagenase, hyaluronidase, b-lactamase |
Comparison of Eukaryotic vs Prokaryotic Membrane Lipids |
-Eukaryotic membranes -Phosphatidylcholine (PC) -Contain sterols -Prokaryotic -Phosphatidylethanolamine (PE) -Targeted by polymyxins -Phosphatidylglycerol (PG) -Cardiolipin -Do not contain sterols, with the exception of mycoplasmas and Helicobacter |
Molecules Commonly Requiring Active Transport |
-Iron and other metals -Ions (Na+, H+, etc.) -Amino acids/ dipeptides -Transporters specific for one or a small group of related amino acids -Sugars -Vitamins |
Efflux Pumps |
-All organisms have efflux pumps -Physiological roles (not completely understood) -Extrusion of toxic metabolites -Heavy metals -Roles in pathogenesis -Efflux of bile salts -Up-regulated following phagocytosis -Resistance to antimicrobial agents -MDR organisms express high levels of efflux pump proteins -Antibiotics, antiseptics, solvents, and detergents can be substrates -Development of “helper drugs” -Inhibition of efflux pumps renders bacteria susceptible to antibiotics |
Peptidoglycan Layer |
-The peptidoglycan layer is critical for resistance to osmotic stress -Consists of: amino acids (hence, “peptido-”) sugars (“glycan”) Other molecules may be inserted into this structure -A very important target for antibiotics -Has pyrogenic activity Repeating structure with crosslinks gives rigidity Structure is NOT impermeable, and permits diffusion |
Properties of Peptidoglycan |
-Usually only 1-3 layers thick in G-; Up to 10x thicker in G+ -Mechanical properties more similar to viscous gel than crystalline structure (i.e., it can stretch) -Proteins <50 kDa can diffuse across PG, along with DNA, nutrients |
Lysozyme |
-Gram positive organisms are most sensitive -Lysozyme can cross the outer membrane of G- after osmotic shock and EDTA treatment |
Transpeptidation reaction inhibited by b-lactam antibiotics |
Penicillin binding proteins (PBP)-bacterial transpeptidases and carboxypeptidases which are inhibited by penicillin
-b-lactam ring resembles the transition state of D-alanyl-D-alanine which
occurs during transpeptidation reaction |
