MicroBiology Mod. 2

Prokaryotes vs Eukaryotes

Prokaryotes:

• one circular chromosome, not in a membrane

• No histones (except Archaea)

• No organelles

• Bacteria: peptidoglycan cell walls

• Binary Fission

Eukaryotes:

• Paired chromosomes in nuclear membrane

• Histones

• Organelles

• Polysaccharide cell walls

• Mitotic Spindle

Coccus

Round bacteria

Bacillus

Rod-like bacteria

Spiral

Spiral shaped bacteria

• Vibrio - bent or C-shaped

• Spirillum - rigid cell wall, use external flagella to move

• Spirochete - flexible cell wall, internal flagella (axium fillament) for movement

Pleomorphic

Multiple shapes at once

e.g. coccobacilli

Arrangements: (due to how they divide)

Pairs:

• diplococci (pair and round)

• diplobacilli (pair and rod-like)

Chains:

• Streptococci (chain and round)

• Streptobacilli (chain and rod-like)

Clusters:

• Staphylococci (cluster and round)

Cocci Specific:

Sarcina:

• cube-shaped

Tetrad:

• square shaped

Glycocalyx

Not every bacteria cell has one

• pod/husk outside the cell wall

• a layer of material containing substantial amounts of sticky carbohydrates (allows it to stick to surfaces or a host)

• capsule - neatly organized glycocalyx that prevents phagocytosis (when specialized cells engulf, internalize, and destroy large particles, like bacteria and viruses)

• slime layer - loose and unorganized glycocalyx where the extracellular polysaccharide allows cells to attach

• helps induce disease/ increase virulence factor

Flagella

Usually on bacilli and spirillum

• Outside the cell wall

• made of chains of flagellin (a protein in prokaryotes)

3 Basic Parts:

• Filament - the long, outermost region that contains the protein flagellin arranged in several chains that form a helix around a hollow core

• Hook - consisting of a different protein, where the filament is attached to

• Basal Body - anchors the flagellum to the cell wall and plasma membrane (composed of a small central rod inserted into a series of rings: 2 pairs, outer and inner, of rings if gram negative and 1 inner pair of rings if gram positive)

Flagella proteins are H. antigens

How Flagella help the cell move

Rotates from the basal body

• Run - swim in a direction (counterclockwise)

• Tumble - switch direction (clockwise)

• Allow the cell to move toward or away from stimuli (taxis)

• Stimuli include chemicals (chemotaxis) and light (phototaxis)

• Listen to chemotactic signals: if positive (attractant), they go towards with many runs and few tumbles. If negative (repellent), they move away with more tumbles than before.

Flagella Arrangement

Atrichous - without flagella

Monotrichous - single flagellum at one end (polar)

Amphitrichous - one flagellum at both ends (polar)

Lophotrichous - a tuft of flagella at one end (polar)

Peritrichous - distributed all around the cell

Axial Filaments

• bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell

• in spirochetes

• called “endoflagella”

• anchored at one end of the cell

• rotation causes the cell to move

Fimbriae

• allow attachment (involved in forming biofilms)

Pili

Used for motility

• gliding motility

• twitching motility

Transfer DNA

Cell Wall

• Prevents osmotic lysis (changes in osmotic pressure causing bursting)

• made of peptidoglycan (a repeating sugar molecule - polymer of disaccharide - linked by polypeptides, or proteins)

Gram positive cell wall

• thick layer of peptidoglycan (on the exterior surface of the cell)

• teichoic acid, integrated for support and rigidity, consist of alcohol and phosphate

• lipoteichoic acid in the periplasmic space

Gram negative cell wall

• two plasma membranes

• thin peptidoglycan layer in the periplasmic space (makes it susceptible to breakage)

• lipopolysaccharide (LPS) in the outer/secondary membrane (phospholipids on the inside facing the periplasm and LPS on the outside acting as a physical and chemical barrier)

Gram stain mechanism

Crystal violet-iodine crystals form in the cell

In gram positive:

• alcohol dehydrates peptidoglycan

• CV-1 crystals do not leave, staining it purple

In gram negative:

• alcohol dissolves the outer membrane and leaves holes in the peptidoglycan

• CV-1 washes out

• stained pink/red after w/ another stain

acid fast cell wall

• Mycobacterium

• These bacteria contain high concentrations ​​(60%) mycolic acid in their cell wall that prevents the uptake of dyes, including those used in the Gram stain

• the mycolic acid forms a layer outside of a thin layer of peptidoglycan

• the hydrophobic lipid cell wall allows mycobacterium to clump together and stick to the walls of a flask

acid fast stain

• used to identify bacteria of the genus Mycobacterium

• stained with carbolfuchsin, which penetrates bacteria more effectively when heated.

• carbolfuchsin penetrates the cell wall, binds to the cytoplasm, and resists removal by washing with acid-alcohol.

• Acid-fast bacteria retain the red color of carbolfuchsin because it’s more soluble in the cell wall’s mycolic acid than in the acid-alcohol.

• If the mycolic acid layer is removed from the cell wall of acid-fast bacteria, they will stain gram-positive with the Gram stain.

Lysozyme

• found in human sweat and tears)

• digests the disaccharide in peptidoglycan

• This act is analogous to cutting the steel supports of a bridge with a cutting torch: the gram-positive cell wall is almost completely destroyed by lysozyme.

Protoplast

• wall-less gram positive cell

• cell wall destroyed by lysozyme

• susceptible to osmotic lysis when placed in a hypotonic environment (cell bursting when solute concentration is higher inside the cell and water rushes in to dilute the concentration)

Spheroplast

• Have lost most of the cell wall but retain portions of the outer membrane

• when lysozyme is applied to Gram negative bacteria

• consists of the cellular contents, plasma membrane, and remaining outer wall layer

• susceptible to osmotic lysis when placed in a hypotonic environment (cell bursting when solute concentration is higher inside the cell and water rushes in to dilute the concentration)

L forms

• of the genus proteus

• partially or completely lose cell walls and can sometimes revert to the normal form once damaging condition of removed

• swells into irregular shapes

• develop in response to penicillin (which inhibits cell wall formation) or lysozyme (which digests peptidoglycan in the cell wall)

• susceptible to osmotic lysis when placed in a hypotonic environment (cell bursting when solute concentration is higher inside the cell and water rushes in to dilute the concentration)

Mycoplasma

• Naturally lack a cell wall and are not produced by lysozyme treatment

• smallest form of bacteria

Damage to cell wall summary

• Protoplast = Purely no wall (cell wall completely removed)

• Spheroplast = Some wall remains (Gram-negative, outer membrane retained)

• L-form = Lost wall (partially or completely, often reversible)

• Mycoplasma = Missing wall naturally (no cell wall to begin with)

Penicillin (in regards to cell wall damage)

• targets cell wall construction and inhibits peptide bridges in peptidoglycan

• dos not affect gram negative cell walls

Plasma membrane structure

Phospholipid bilayer - the polar hydrophilic heads are on the two surfaces of the lipid bilayer, and the nonpolar hydrophobic tails are in the interior of the bilayer.

• 3 Carbon glycerol

• 2 Fatty acid chains

• Phosphate group

Peripheral proteins - one side or the other

Integral proteins - permanently embedded into the membrane

Transmembrane proteins - spans the entire plasma membrane

Fluid mosaic model of the plasma membrane

Fluid mosaic model

• the fatty acid tails cling together, so phospholipids in the presence of water form a self-sealing bilayer allowing breaks and tears in the membrane to heal themselves

• Membrane is viscous, allowing proteins to move freely enough to perform their functions without destroying the structure of the membrane.

• Proteins move to function

• Phospholipids rotate and move laterally

Plasma membrane functions

• Selective permeability allows passage of some molecules

• Enzymes for ATP production

• Photosynthetic pigments on infoldings called chromatophores or thylakoids

• Damage to the membrane by alcohols, quaternary ammonium (detergents) and polymyxin antibiotics causes leakage of cell contents

Semi-permeable membrane

some substances are able to cross while others are not

Simple diffusion

• a form of passive transport

• movement of a solute from an area of high concentration to an area of low concentration

• transports small molecules, such as oxygen and carbon dioxide, across the cell membrane

Fascilitated diffusion

• a form of passive transport

• solute combines with a transporter protein in the membrane

• movement of ions or large molecules across the plasma membrane

• does NOT expend energy

Active transport

requires a transporter protein and ATP

• it expends energy

• low concentration to a high concentration, so it goes AGAINST the concentration gradient

Osmosis

movement of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration

Osmosis: isotonic solution

no net movement of water occurs

Osmosis: hypotonic solution

water moves into the cell

• high solute concentration inside the cell

• low solute concentration outside the cell

• if the cell wall is strong, it contains the swelling

• if the cell wall is weak/damaged, the cell bursts (osmotic lysis)

Osmosis: hypertonic solution

water moves out of the cell

• low solute concentration inside the cell

• high solute concentration outside the cell

• causes the cytoplasm to shrink when water rushes out of the cell to dilute the high concentration outside (called plasmolysis)

plasmolysis

the shrinkage of a cell's cytoplasm away from the cell wall due to water loss by osmosis when the cell is placed in a hypertonic solution

In bacteria:

• Water moves out of the cell into the surrounding environment.

• The cytoplasmic membrane pulls away from the cell wall.

• Cell growth and metabolism may stop, although the cell is not necessarily killed.

This is one reason why high concentrations of salt or sugar can help preserve food—they create a hypertonic environment that causes plasmolysis in many microorganisms.

Endospores

Resting (Dormant) cells

• Metabolically inactive

• Resistant to desiccation, heat, chemicals

• Sporulation occurs during stress (unfavorable environment)

• Bacillus, Clostridium

• Sporulation: Endospore formation

• Germination: Return to vegetative state (occurs when spore finds a favorable environment)

Inside a bacteria cell

• Nuclear area with DNA (nucleoid)

• Ribosomes for protein synthesis

• Cytoplasm is the substance inside the plasma membrane

Prokaryotic Ribosomes

Protein synthesis

• 70S (Composed of over 30 proteins and rRNA)

• S = Svedberg Units (Centrifuge sedimentation)

• 50S + 30S subunits

Inclusions:

Cells may accumulate certain nutrients when they are plentiful and use them when the environment is deficient.

(reserve deposits)

• Metachromatic granules (volutin) - phosphate reserves

• Polysaccharide granules - energy reserves

• lipid inclusions - energy reserves

• sulfur granules - energy reserves

• carboxysomes - Ribulose 1,5- diphosphate carboxylase for CO2 fixation

• gas vacuoles - protein-covered cylinders

• magnetosomes - iron oxide (destroys H2O2)

Eukaryote: nucleus

largest structure in the cell, and contains almost all of the cell’s hereditary information (DNA)

• contains chromosomes wrapped around proteins called histones

• genetic material is a threadlike mass called chromatin until it gets ready to divide where it condenses into chromosomes

Eukaryote: Rough Endoplasmic reticulum

responsible for synthesis, folding, and initial modification of proteins

• contains ribosomes

Eukaryote: Smooth Endoplasmic reticulum

synthesizes phospholipids, fats, and steroids

• does not have ribosomes

Eukaryote: golgi apparatus

modifies, sorts, packages, and ships proteins and lipids to their final destinations inside or outside the cell

Eukaryote: lysosome

digestive enzymes

• found only in animal cells

Eukaryote: vacuole

brings food into cells and provides support

• derived from the golgi apparatus

• some serve as temporary storage organelles for substances such as proteins, sugars, organic acids, and inorganic ions

• others form during endocytosis to help bring food into the cell

• store metabolic wastes and poisons

• take up and excrete excess water to prevent osmotic lysis

Eukaryote: cytoplasm

where all the organelles are stored

Eukaryote: flagella and cilia

• projections are few and are long in relation to the size of the cell, they are called flagella (algae)

• projections are numerous and short, they are called cilia (protozoa)

Eukaroyte: ribosomes

free ribosomes - unattached to any structure in the cytoplasm.

• synthesize proteins used inside the cell.

membrane-bound ribosomes - attach to the endoplasmic reticulum.

• synthesize proteins destined for insertion in the plasma membrane or for export from the cell.

80S ribosomes

• large 60S sub unit containing three molecules of rRNA

• smaller 40S subunit with one molecule of rRNA.

Eukaryote: mitochondria and chloroplasts

• produce ATP

• perform photosynthesis

Eukaryote: peroxisome

oxidizes various organic substances

protect others parts of the cell from toxic effects of H2O2.

Molds

The fungal thallus (growth) consists of hyphae (long strands of cells)

• a mass of hyphae is a mycelium

Yeasts

• Unicellular fungi

• Fission yeasts divide symmetrically

• Budding yeasts divide asymmetrically

Fungal Diseases (Mycoses)

Systemic mycoses - Deep within body

Subcutaneous mycoses - Beneath the skin

Cutaneous mycoses - Affect hair, skin, nails

Superficial mycoses - Localized, e.g., hair shafts

Opportunistic mycoses - Caused by normal microbiota or fungi that are usually not pathogenic

Viruses

• Don’t fit our definition of a living organism

• They are composed of Nucleic Acid & Protein

• Viruses are obligate intracellular ‘parasites’

• No metabolic ability

• They infect every type of life form: animals to algea

• Each has a “Host Range”

• Evolve quickly

• Genome consists of singe or double stranded DNA or RNA

• capsid - protein shell enclosing the viral genome (built from proteins called capsomeres)

Some have lipid membranes:

• viral envelope (contains capsid and aids in entry to the cell)

Prions

Prions - proteins that cause brain diseases in

mammals

• Infectious proteins that build up in nervous tissue

• Propagate by converting normal proteins into the prion

version

• Creutzfeldt-Jakob disease – acquired (vCJD) or

inherited

• PRNP gene  PrP normal protein

• Scrapie; Mad Cow disease (BSE)