Microbiology Ch. 3

Filamentous Protein Appendages: Flagella Chemotaxis

1. Bacteria sense chemicals and move accordingly 1) Nutrients may attract, toxins may repel 2) Movement is series of runs and tumbles

Permeability of Lipid Bilayer: Osmosis

1. Diffusion of water across selectively permeable membrane due to unequal solute concentrations. 2. Three terms to describe conditions outside the cell: - Hypertonic: Water moves inside the cell: - Isotonic: No net movement of water - Hypotonic: Water moves outside the cell: Plasmolysis

Internal Structures: Nucleoid

Chromosome forms gel-like region • Single circular, double-stranded DNA packed tightly via supercoiling; Haploid DNA • Lacks nuclear membrane • Lacks histones

The Cytoplasmic Membrane

Cytoplasmic membrane Serves as semipermeable membrane: controls movement of molecules across the cell Composition: Phospholipid bilayer embedded with proteins Fluid mosaic model: proteins drift about in lipid bilayer Proteins serve numerous functions 1. Selective gates 2. Sensors of environmental conditions 3. Enzymes for ATP synthesis (Electron Transport Chain and Proton Motive Force)

Permeability of Lipid Bilayer

Cytoplasmic membrane is selectively permeable 1. O2, CO2, N2, small hydrophobic molecules, and water pass freely through lipid layer 2. Other molecules must be moved across membrane via transport systems

Capsules and Slime Layers

Gel-like layer outside cell wall in some bacteria 1. Capsule: distinct, gelatinous 2. Slime layer: diffuse, irregular 3. Mostly composed of glycocalyx (sugar shell) although some are polypeptides 4. Functions: 1) Allow bacteria to adhere to surfaces. Once attached, cells can grow as biofilm (Polysaccharide encased community). Example: dental plaque 2) Some capsules allow bacteria to evade host immune system (phagocytosis) 3) Protect from dehydration 4) Nutrients under adverse conditions

Internal Structures: Storage granules

accumulations of polymers 1. Synthesized from nutrients available in excess 2. For Example 1) Glycogen granules: made of excess glucose 2) Poly-β-hydroxybutyrate granules (disposable plastic) 3) Volutin granules: also called as metachromatic granules made of polyphospahtes

Internal Structures: Plasmids

are circular, extrachromosomal dsDNA • Usually much smaller; few to several hundred genes

Internal Structures: Ribosomes

are involved in protein synthesis • Relative size expressed as S (Svedberg) • Prokaryotic ribosomes are 70S • Made from 30S and 50S • Eukaryotic ribosomes are 80S • Important medically: antibioticsimpacting 70S ribosome do notaffect 80S ribosome

Gram-positive

cell wall has thick peptidoglycan layer and teichoic acids

Inernal Structures: Gas vesicles

controlled to provide buoyancy

Cell Wall

strong, rigid structure that maintains shape and prevents cell lysis. architecture is the basis for distinguishing two main types of bacteria • Gram-positive • Gram-negative Made from peptidoglycan --> Found only in bacteria

Gram-negative

very thin peptido-glycan layer and unique outer membrane

Permeability of Lipid Bilayer: Simple Diffusion

1. Movement of solutefrom high to low concentration 2. Speed depends on concentration

Internal Structures: Endospores

1. Unique type of dormant structure 2. Resistant to heat, desiccation, toxic chemicals, UV radiation and boiling 3. Members of Bacillus, Clostridium produce 4. May remain dormant for 100 years or longer 5. Endospores that survive cangerminate to become vegetative cell 6. Found virtually everywhere (soil) Not a mechanism of Reproduction 2. Important in medical and canning industry 3. Botulism, tetanus, gangrenes, and anthrax are all caused by endospore formers. 4. Resistant to heat, desiccation, toxic chemicals, UV radiation and boiling 5. How to destroy spores?

peptidoglycan

Alternating series of subunits form glycan chains • N-acetylmuramic acid (NAM) • N-acetylglucosamine (NAG) 2. Tetrapeptide chain (string of four amino acids) 3. Peptide bridges or crosslinks

Filamentous Protein Appendages: Flagella

Appendages not essential, but give advantage 1. Spin like propellers to move cell 2. Some important in disease Eg. Helicobacter pylori 3. Numbers and arrangements help with characterization 4. Peritrichous: distributed over entire surface 5. Polar flagellum: single flagellum at one end of cell 6. Some bacteria have tuft at one or both ends Three parts 1. Filament 2. Hook 3. Basal body

Cell Wall Type and the Gram Stain

At the end of Gram staining procedure, Gram positive cells appear purple and Gram negative cells appear pink

periplasmic space

Between cytoplasmic membrane and outer membrane: Filled with gel-like periplasm

Gram Negative Wall: Outer membrane

Bilayer made from lipopolysaccharide (LPS) 2. Includes Lipid A (immune system recognizes) and O polysaccharide (can be used to identify species or strains) 3. Important medically: signals immune system of invasion by Gram-negative bacteria 1) Small levels of LPS elicit appropriate immune response to eliminate bacteria from human body 2) Large amounts of LPS accumulating in bloodstream can yield deadly response 3) LPS (lipid A) is called endotoxin Outer membrane blocks passage of many molecules including certain antibiotics • Small molecules and ions can cross via porins

Directed Movement of Molecules Across Cytoplasmic Membrane through Transport Proteins

Most molecules must pass through proteins functioning as selective gates 1. Proteins may be called permeases, carriers 2. Highly specific: carriers transport certain molecule type 3. 3 types: Facilitated diffusion (passive), Active Transport (active), Group Translocation (active) Facilitated diffusion is a form of passive transport Active transport Two main mechanisms 1. Use proton motive force 2. Use ATP (ABC transporter) Group Translocation: Chemically alter compound 1. Phosphorylation 2. Unique to bacteria

Two Types of Transport across Cytoplasmic Membrane

Passive Transport 1. Along the concentration gradient 2. Does not requires energy 3. Examples: Simple diffusion, Osmosis, Facilitated diffusion Active Transport 1. Against the concentration gradient 2. Requires energy 3. Examples: Active Transport using either PMF or ATP, Group Translocation

Antibacterial Substances That Target Peptidoglycan

Peptidoglycan makes good target since unique to bacteria Penicillin interferes with peptidoglycan synthesis 1. Prevents cross-linking of adjacent glycan chains 2. Usually more effective against Gram-positive bacteria than Gram-negative bacteria • Outer membrane of Gram-negatives blocks access • Derivatives have been developed that can cross Lysozyme breaks bonds linking glycan chain • Enzyme found in tears, saliva, other bodily fluids

Filamentous Protein Appendages: pili

Pili are shorter than flagella 1. Twitching motility, gliding motility involve pili 2. Sex pilus for DNA transfer Fimbriae: allow surface attachment termed

Unusual Cell Walls

Some bacteria contain acid fast cell wall 1. Cell walls contain waxy lipids, such as mycolic acids, in addition to peptidoglycan 2. Not affected by many antibacterial substances 3. Include genus Mycobacterium Members of domain Archaea have variety of cell walls 1. Probably due to wide range of environments • Includes extreme environments 2. No peptidoglycan 3. Some have similar molecule pseudopeptidoglycan

Bacteria That Lack a Cell Wall

Some bacteria lack a cell wall 1. Mycoplasma species have extremely variable shape 2. Penicillin, lysozyme do not affect 3. Cytoplasmic membrane contains sterols that increase strength

Internal Structures: Sporulation

Sporulation triggered by carbon, nitrogen limitation 1. Starvation conditions begin 8-hour process 2. Endospore layers (spore coat) prevent damage 3. Cortex maintains core in dehydrated state, protects from heat 4. Core has small proteins that bind and protect DNA 5. Calcium dipicolinate seems to play important protective role Germination triggered by heat, chemical exposure