Robert Hooke

Antoni van Leeuwenhoek

Amateur Microscopist

First to coin term "cell"

Published findings in Micrographia

Dutch Drapery Merchant 

Used Lens to peer into a drop of lake water:

First to see live microbes

First to describe bacteria

Called organisms "animalcules"

Francesco Redi

Louis Pasteur

John Tyndall

Demonstrated worms found on rotting meat cames from eggs of flies landing on meat:

Proved this by placing rotting meat in jars and covered one jar with fine gauze.

Gauze prevented flies from depositing eggs i.e. no eggs - no worms

Father of Modern Microbiology

Demonstrated that air is filled with microorganisms: 

Proved by filtering air in cotton plug

Swan Necked Flask

discovered endospore: organism that had secondary life form that could endure long periods of boiling

Concluded different infusions required different boiling times

1854-1914

Time of great interest in study of microorganisms 

Between 1875-1918 most disease causing bacteria were discovered

Work on viruses began

Led to initiation of prevention and treatment of disease

Developed science of medical microbiology: first to show that a specific bacterium was cause of specific disease (ex. bacillus anthracis, anthrax)

Worked with TB and anthrax

Developed procedures for growing bacteria in pure culture medium

Rules for establishing that a specific organism is the cause of a specific disease:

1. Organism must be isolated from diseased organism in all cases

2. Organism must be grown in pure culture

3. When introduced back into animal model, organism must cause same symptoms as in original illness

4. Organism must be re-isolated in experimental infection in model

Organisms in each domain share certain properties:

Eukarya

Bacteria (Prokaryotes) 

Archaea (Prokaryotes)

Too small to be seen without microscope

Two groups: 

Living (organisms)

Non-living (Infectious agents)

Single Cell Organism

Replicate by Binary Fission

Genetic material not contained in membrane bound organelle (no nuclear membrane or nucleoid)

Bacteria (Eubacteria) and Archaea ("extremophiles")

Microbes:

Fungi

Yeast 

Protozoa

Helmenths

(non-living)

Viruses

Viroids

Prions ~ newest to have been discovered

Microbes have tremendous impact on human existence; they have killed more people than have ever been killed in war

Microorganisms have an important role in the production of oxygen and usable nitrogen

Microorganisms are decomposers and are responsible for the breakdown of a wide variety of material

Estimated 500-1000 species of bacteria reside in and on the human body

Bacteria out number cells in the body 10:1; compete with other organisms for food and space

Keep disease causing organisms from breaching host defenses

Some bacteria and viruses use human body as habitat for multiplication, persistance and transmission

Food Production: fermentation of milk to produce yogurt, cheese, buttermilk; beer, wine

Bioremediation: use organisms to degrade environmental waste, clean up oil spills, treat radioactive waste

Viral disease smallpox once a leading killer ~ no cases since 1977

Plague: major killer in history ~ fewer than 100 die worldwide

1. HIV

2. Tuberculosis

3. Malaria

Substance that consists of a single type of atom 

92 Naturally Occuring Elements

Four Primary Elements: 

Carbon

Nitrogen

Oxygen

Hydrogen

Basic unit of all matter 

Made up of three major components:

Protons

Neutrons

Electrons (spinning in clouds)

Atoms are most stable when the outer orbital contains the maximum number of electrons ~ 1st shell: two

2nd, 3rd, etc shell: eight

No full outer shell? UNSTABLE. So gain/lose/share electrons to form bonds and achieve a more stable state. Molecules formed when atoms bond together. 

Strongest type of bond

 Achieve stability through the sharing of electrons between atoms. 

Requires significant energy to break, usually in the form of heat. 

Bonds can be polar or nonpolar.

Equal attraction for the shared electrons.

Bonds formed between identical atoms or between atoms that have similar attraction for electrons.

One atom has a greater attraction to the electrons than the other, ie greater electronegativity. This produces a slight charge different within the molecule ie molarity, and a dipole moment is formed. 

Ex. Water: Hydrogens have a slight positive charge while oxygen has a slight negative charge. 

Formed by gaining or losing electrons ~ electrons completely leave first atoms and become part of outer orbital of second atom. This loss/gain leads to charged atoms or ions. These charged atoms are attracted to each other and form a bond between ions ie an ionic bond or salt bridge.

Approximately 100x weaker than covalent bonds, dissociate in water at room temperature.

Weak biological bonds, but if you have a lot it will stabilize and hold molecules together firmly, such as in DNA; like numerous stitches in clothing: one stitch vs many. 

Formed from attraction of positively charged hydrogen atoms to negatively charged atoms or molecules (usually oxygen or nitrogen)

Hydrogen bonds hold molecules together, covalent bonds hold atoms together. 

Constantly being formed and broken at room temperature. 

Most important molecule

Universal Solvent

Allow reactions in our body to occur

Makes up over 70% of all living organisms by weight

Importance of water depends on its unusual bonding properties

Hydrogen bonds form between positively charged hydrogen of one molecule and negatively charged oxygen of another creating a latice formation.

Hydrogen bonding creates a polar molecule; polar nature accounts for the ability to dissolve numerous compounds.

Molecules that dissolve in water must contain charged atoms ie hydrophillic molecules.

Ex. NaCl ~ dissolves in water forming Na+ and Cl- ions which become surrounded by water and can no longer nond to each other. 

pH = -log[H+]

Measured on a logarithmic scale of 0 to 14 (0 ~ highly acidic, 14 ~ highly basic or alkaline)

When H+ and OH- ions are equal in soultion = neutral solution

High H+ = acid, High OH- = base

Biological Macromolecules are divided into three classes: 

Proteins

Polysaccharides (carbohydrates)

Nucleic Acids

**Lipids**

Macromolecules are very large.

All are considered polymers made up of monomeric subunits connected through covalent bonding. 

Dehydration Synthesis: joining subunits together by removing water to allow the polymer to grow 

Hydrolysis: adding water to break bonds between subunits, shrinking the polymer

Constitute over 50% of cell dry weight

Made up of amino acid subunits 

Most versatile, some responsibilities include:

Act as enzymes, catalyzing reactions

Composition and shape of certain bacterial structures

Gene regulation

Nutrient procurement

Molecules of communication

Proteins are composed of numerous combinations of 20 naturally occuring amino acids

Protein shape and ultimately its function depends on the shape of the sequence of amino acids, ie shape determines function.

Always linear, in a chain.

All amino acids have the following shared features: 

a carboxyl group (COO-)

an amino group (NH2-)

a central carbon 

a side chain or R group (varies in length, this is what differentiates the amino acids)

Amino acids are subdivided based on similarities of side chain. 

Amino acids are held together by peptide bonds ~ a unique type of polar covalent bond. 

Formed between the interaction of the carboxyl group of one amino acid and the amino group of the following amino acid.

Reaction causes the release of water and formation of peptide bond. 

Sequence of amino acids connected by peptide bonds

In large part determines other protein features

"Beads on a string"

Chain grows only in one direction 

Primary structure folds into new configuration that results from weak bonds formed between amino acids.

Alpha Helix: helical or spiral structure

Beta Sheet: pleated structure

Stabilized by hydrogen bonds between carbonyl and amide groups along the polypeptide backbone (peptide bonds). 

Three dimensional structure 

Two major shapes: 

Globular

Fibrous

Becomes a functional protein

Multiple polypeptides held together with covalent (disulfide bonds) or weak bonds to held stabilize structure. 

Sulfhydro groups make these bonds possible. 

Proteins must have a specific shape to have a proper function. 

Environmental conditions (high pH, high salt, high temp) can break bonds within the protein, causing shape change. 

Shape change causes protein to stop functioning, called denaturation. 

Denaturation can be reversible or irreversible, determined by environment, however, typically will not reverse. 

Ex. Chicken Egg: heat to denature protein before you eat. 

SUGARS

A diverse group of molecules with various sizes 

Five carbon sugars form subunits of nucleotides

Play an important role in all organisms: 

- Common and important source of food and energy (even for bacteria)

- Form part of nucleic acids 

- Form part of bacterial cell wall

Contain carbon, hydrogen and oxygen in 1:2:1 ratio (CH2O)

Single Carbohydrate Molecule (simple sugar) 

Classified by the number of carbons in molecule 

Most common monosaccharides: 

5 Carbon Sugars

6 Carbon Sugars ~ common in biological systems (ex. glucose, mannose, galactose, fructose)

Produced by joining two monosaccharides through dehydration synthesis ie water is lost

Most Common in Nature:

Lactose (glucose + galactose)

Sucrose (glucose + fructose)

Maltose ~ less common (glucose + glucose)

(+) represents glycosidic bond 

Chains of monosaccharides

Cellulose:

- most abundant organic molecule on earth

- polymer of glucose molecules

- principle constituent in plant cell wall

- we depend on enzymes of other animals to break down so we can use (termites)

Glycogen: 

- carbohydrate storage molecule of humans, animals and some bacteria

- polymer of glucose subunits

Dextran: 

- storage molecule of carbon and energy for some bacteria 

- polymer of glucose subunits

**Oligosaccharide: short chain of carbohydrates, a few monosaccharides**

Two Types: 

- DNA (Deoxyribonucleic Acid) ~ carries genetic code in all cells

- RNA ~ decodes sequence of amino acids to produce proteins 

Subunits of nucleic acids are nucleotides.

 Nucleotides are composed of three units:

- Nitrogen containing ring compound, nitrogenous base:

~ purine (adenine and guanine)

**AGgies are Pure**

~ pyrimidine (thymine and cytosine)

- Five carbon suger molecule, deoxyribose

- Phosphate molecule

**Minus phosphate group? Nucleoside**

Nucleotides are joined through covalent bonding; bond created between phosphate of one nucleotide and sugar of the adjacent through dehydration synthesis.

Phosphate molecule acts as a bridge between the #3 (3') carbon of one sugar and the #5 (5') carbon of the adjacent.

This results in a sugar phosphate backbone.

**3' ~ OH group/5' ~ phosphate group** 

Master molecule that determines the specific properties of the cell.

In living organisms, is a double stranded helical molecule.

Strands are held together by hydrogen bonding between nitrogen bases.

Specific pairing between bases: 

A-T or T-A

G-C or C-G

Bases are complementary

Involved in decoding DNA. 

Structure is similar to DNA, but differs in a number of ways:

- Thymine is replaced by Uracil

- The sugar ribose replaces deoxyribose

- RNA is generally shorter

- exists as single stranded molecule, not double stranded

Critical component of the cell membrane (membranes act as gatekeepers for the cell determining what enters and leaves the cell).

Heterogeneous group of molecules ie made up of different subunits.

Its defining feature is that it is insoluble in water (hydrophobic ~ water hydrogen bonds to itself and forms cage around lipid)

Smallest of the four macromolecules.

Can be divided into two general classes: simple lipids and compound lipids.

Contain only carbon, hydrogen and oxygen.

Most common are called fats:

- solid at room temperature

- made of glycerol and fatty acids

Fatty acids are long hydrocarbon chains plus an acid group (COOH) at the end. 

Glycerol is a carbon hydrogen chain with three hydroxyl (OH) groups attached. This allows for the binding of three fatty acids to one glycerol ie triglyceride. 

Steroids are also considered simple lipids. They differ from fats in structure and function, structure consists of four membered ring. Classified as lipid because steroids are insoluble in water. If one of the rings has a hydroxyl (OH) group attached to it, it is classified as a sterol (ex. cholesterol). 

Two Groups: 

Saturated ~ no double bonds, tails packed tightly so solid at room temperature (fats)

Unsaturated ~ double bonds, kinks prevent tight packing so liquid at room temperature (oils)

Monounsaturated: one double bond

Polyunsaturated: more than one double bond

Contains fatty acids, glycerol and other elements.

Phospholipid: most important compound lipid

- made up of a phosphate and two fatty acids attached to a glycerol molecule

- phosphate head is polar and soluble in water (hydrophilic)

- fatty acids are nonpolar and insoluble in water (hydrophobic)

Major component in lipid cell membrane.

Membrane is a double or bilayer of phospholipids.

Hydrophilic heads orient towards internal and external environments. 

Hydrophobic tails orient themselves away from aqueous environment towards each other.

Membrane acts as a barrier to the entry and exit of cellular substances. 

Light Microscopy: light passes through specimen, then through series of magnifying lenses. Most common and easiest to use is the brightfield microscope. 

Important Factors:

Magnification 

Resolution 

Contrast 

Compound microscope has two magnifying lenses: 

Occular lens

Objective lens

Most bright-field scopes have four magnifications of objective lenses ~ 4x, 10x, 40x and 100x

Lenses combine to enlarge objects, magnification is equal to the factor of the occular times the objective. 

Bright-field scopes have condenser lens which has no affect on magnification but is used to focus illumination on specimen. 

Usefulness of microscope depends on its ability to resolve two objects that are very close together. 

Resolving power is defined as the minimum distance existing between two objects where those objects still appear as separate objects.

Resolving power determines how much detail can be seen. 

Equation: D=.61λ/ηsinΘ

λ=wavelength of illuminating light

η=refractive index

sinΘ=1.00

Resolution depends on the quality of the lensesand wavelength of illuminating light ie how much light is released from the lens

Max resolving power of most bright-field microscopes is 0.2 μm. (This is sufficient to see most bacterial structures, but too low to see viruses)

Resolution is enhanced with lenses higher than 100x with the use fo immersion oil. (Oil reduces light refraction by bridging the gap between specimen slide and lens; oil has nearly the same refractive index as glass. 

Reflects the number of visible shades in a specimen. 

Higher contrast achieved for microscopy through specimen staining.

Phase-Contrast Microscope

Interference Microscope

Dark-Field Microscope

Fluorescence Microscope

Confocal Scanning Laser Microscope

Amplifies differences between refractive indexes of cells and surrounding medium. 

Uses sets of rings and diaphragms to achieve resolution. 

This microscope causes specimen to appear three dimensional, depends on differences in refractive index. 

Most frequently used interference scope is Nomarski differential interference contrast. 

Reverse Image ie specimen appears bright on a dark background, like a photographic negative. 

Achieves image through a modified condenser. 

Used to observe organisms that are naturally fluorescent or are flagged with fluorescent dye. 

Fluorescent molecule absorbs ultraviolet light and emits visible light. Image fluoresces on dark background. 

Uses electromagnetic lenses, electrons and fluorescent phosphorescent screen to produce image. 

Resolution increased 1,000 fold over brightfield microscope to about **.3nm**

Magnification increased to 100,000x.

Two Types: 

- transmission

- scanning 

Used to observe fine detail. 

Directs beam of electrons at specimen and electrons pass through or scatter at surface. 

Shows dark and light areas, darker areas more dense. 

Specimen preparation through thin sectioning and freeze fracturing or freeze etching. 

Used to observe surface detail.

Beam of electrons scan surface of specimen which is convered with metal, usually gold. 

Electrons are released and reflected into viewing chamber. 

Some atomic microscopes capable of seeing single atoms. 

Cells are frequently stained to observe organisms.

Stains are made of organic salts.

Dyes carry (+) or (-) charge on the molecule, and molecule binds to certain cell structures.

Dyes divided into basic or acidic based on charge. Basic dyes carry positive charge and bond to cell structures that carry negative charge (commonly stain the cell). Acidic dyes carry positive charge and are repelled by cell structures that carry negative charge (commonly stain the background). 

Basic dyes are more commonly used than acidic dyes.

Common basic dyes include: 

Methylene Blue

Crystal Violet 

Safranin

Malachite Green

Simple stain uses one basic stain to stain the cell. This allows for increased contrast between cell and background. All cells stained the same color ie no differentiation between cell types.

Differential Stains are used to distinguish one bacterial group from another. It uses a series of reagents. Two most common Differential Stains: 

Gram Stain 

Acid-Fast Stain

Differentiates bacterial cells.

Most widely used procedure for staining bacteria.

Developed over a century ago by Dr. Hans Christian Gram.

Bacteria separated into two major groups:

Gram Positive ~ stained purple

Gram Negative ~ stained red or pink

Primary Stain: Crystal Violet ~ stains the cell

Mordant: Gram's iodine ~ holds primary stain onto cell

Decolorizer: usually alcohol ~ removes primary dye from gram negative cell

Counter or Secondary Stain: Safranin ~ recolors cells that lose stain through decolorizer

Used to stain organisms that resist conventional staining

Used to stain members of genus Mycobacterium: high lipid concentration in cell wall which prevents uptake of dye, and uses heat to facilitate staining. (Once stained, difficult to decolorize)

Can be used to presumptive identification in diagnosis of clinical specimens

Primary dye: carbol fuchsin ~ colors acid-fast bacteria red

Decolorizer: generally acid alcohol ~ removes stains from non acid-fast bacteria

Counter Stain: methylene blue ~ colors non acid-fast bacteria blue

Capsule Stain: example of negative stain; allows capsule to stand out around organism (ex. india ink)

Endospore Stain: staining enhances endospore; uses heat to facilitate staining

Flagella Stain: staining increases diameter of flagella ie makes more visible

Most Common:

Coccus (plural=cocci): spherical 

Bacillus: rod or cylinder shaped

Others:

Coccobacillus: short round rod

Vibrio: curved rod

Spirillum: spiral shaped

Spirochete: helical shape

Pleomorphic: bacteria able to vary shape 

Prokaryotic cells may form groupings after cell division ie cells adhere together after cell division for characteristic arrangements. This arrangement depends on plane of division. 

Division along a single plane may result in pairs or chains of cells.

Pairs=diplococci

Chains=streptococci

Divisions along two or three perpindicular planes form cubical packets ~ ex. Sarcina genus

Division along several random planes form clusters ~ ex. staphylococcus

Some bacteria live in groups with other bacterial cells, forming multicellular associations. 

Ex. Myxobacteria: form a swarm of cells, allowing for the release of enzymes which degrade organic material. In the absence of nutrients, cells form fruiting bodies. 

Other organisms form biofilms ~ secondary architectures that help organisms stick to objects, protect themselves, obtain nutrients and allow for changes in cellular activity. 

Absence of membrane bounded nucleus; genome of prokaryote sometimes referred to as nucleoid.

Absence of membrane bounded intracellular organelles

Sizes range from 1-10 μm for bacteria

Cell Membrane:

Inner Membrane (both Gr+ and Gr-)

Outer Membrane (only Gr-)

Cell Wall

Periplasmic Space (periplasm; in between inner and outer) ~ only Gr-

Similar to Plasma Membrane

Both bacteria and archaea have cytoplasmic membranes, but phospholipid composition differs between two groups.

- Delicate thin fluid structure

-Surrounds cytoplasm of cell

- Defines boundary; provides compartmentalization of cytoplasmic contents

- Serves as a semi-permeable barrier; barrier between cell and external environment determining which molecules pass into or out of cell.

Structure is a lipid bilayer with embedded proteins composed of two opposing leaflets of phospholipids; each contains a hydrophilic phosphate head and hydrophobic fatty acid tails 

Membrane is embedded with more than 200 proteins.

Proteins function as receptors and transport gates.

Provides mechanism to sense surroundings.

Proteins are not stationary, constantly changing position; called a fluid mosaic model.
Instruments of communication between cell and outside.

 Only a few molecules pass through membrane via simple diffusion; most pass using transport mechanisms that may require carrier proteins and energy.

Process by which molecules move freely across cytoplasmic membrane (through lipid bilayer).

Water, certain gases (O2 and CO2) and small hydrophobic molecules pass through via simple diffusion is don't need a protein.

High concentration to low concentration

Gradient=concentration differences within an area or on either side of a semi-permeable membrane

Diffusion=movement of molecules from an area of high concentration to an area of lower concentration.

Equilibrium=molecules evenly distributed across barrier

Concentration=# particles/volume

The ability of water to flow freely across the cytoplasmic membrane through aquaporins.

Water flows to equalize solute concentrations inside and outside the cell ie water will move from area of low solute concentration to area of high solute concentration.

Water flows across a membrane toward the hypertonic solution.

Membrane also the site of energy production.

Energy produced through series of embedded proteins.

- Electron Transport Chain

- Proteins are used in the formation of proton motive force

- Energy produced in proton motive force is used to drive other transport mechanisms and synthesize ATP

High energy electrons coming from glucose through metabolism force proteins out of cell; them moving against concentration gradient backin into the cell provides energy for cell to do work.

Accumulation of protons outside of plasma membrane.

Transporters allow protons into cell.

Protons either bring in or expel other substances.

Protons fall from higher to lower; potential energy from fall can be used to move molecule against concentration gradient.

Movement of many molecules directed by transport systems.

Transport Systems employ highly selective proteins ie can only transport one kind of molecule.

Transport Proteins aka permeases or carriers, span the membrane.

Most transport proteins are produced in response to need.

Transport systems include facilitated diffusion, active transport and group translocation.

**Rare in Bacteria**

Moves compounds across membrane through transmembrane protein exploiting a concentration gradient ie only moves in one direction.

Flow from area of greater concentration to area of lesser concentration; molecules are transported until equilibrium is reached.

System can only utilize a concentration gradient, it cannot create one.

No energy is required for facillitated diffusion.

Requires specific transmembrane proteins.

Moves compounds against a concentration gradient.

Requires an expenditure of energy.

Two primary mechanisms:

Proton Motive Force

ATP Binding Cassette System (ABC)

Transporter chemically alters the substance as it is transported across the membrane.

Ex. Glucose to Glucose 6 Phosphate

 Uptake of molecule does not alter concentration gradient.

Phosphotransferase system example of group transport mechanism.

- phosphorylates suger molecule during transport; phosphorylation changes molecule and therefore does not change sugar balance across the membrane.  

System of transmembrane proteins that recognize small part of protein called signal sequence.

The signal sequence on the preprotein targets it for secretion and is removed during the secretion process. Once outside the cell, the protein folds into its functional shape.

Extracellular enzymes degrade macromolecules so that the subunits can then be transported into the cell.

Active secretion=molecules chews up mass so bacteria can use it.

Rigis Structure

Surrounds Cytoplasmic Membrane

Determines shape of bacteria

Holds cell together

Prevents cell from bursting

Unique chemical structure (distinguishes Gr+ from Gr-)

Rigidity of cell wall is due to PTG, a compound found only in bacteria.

Basic Structure:

Alternating series of two sugers (linked covalently):

N-acetylglucosamine (NAG)

N-acetylmuramic acid (NAM)

Joined subunits form glycan chain held together by string of four amino acids aka tetrapeptide chain

Composed of plasma membrane and PTG.

Relatively thick layer of PTG, as many as thirty layers.

Regardless of thickness, PTG is permeable to numerous substances.

Teichoic Acid Component:

- gives cell negative charge

- Ribitol phosphate or glycerol phosphate

Only contains a thin layer of PTG.

PTG sandwiched between outer membrane and cytoplasmic membrane.

Region between outer membrane and cytoplasmic membrane is called periplasm (space in between inner and outer leaflet):

- Most secreted proteins contained here

- Proteins of ABC transport system located here

Gr- Cell Envelope:

Plasma Membrane

PTG

periplasm

lipopolysaccharide

Constucted of lipid bilayer:

- much like cytoplasmic membrane but outer leaflet made of lipopolysaccharides NOT phospholipids

- outer membrane also called the lipopolysaccharide layer or LPS layer

LPS serves as barrier to a large number of molecules, small molecules or ions pass through channels called porins.

Portions of LPS medically significant:

- O-specific polysaccharide side chain

- **Lipid A (endotoxin)**

O-specific polysaccharide:

- directed away from membrane, interact with outside

- opposite location of Lipid A

- Used to identify certain species or strains

Lipid A:

- portion that anchors LPS molecule in lipid bilayer

- plays role in recognition of infection

- molecule present with Gr- infection of bloodstream

PTG as a target

- many antimicrobial agents destroy or interfere with synthesis of PTG

Examples include:

Penicillin

Lysozyme

Differences in cell wall account for differences in staining characteristics:

- Gr+ bacterium retain crystal violet-iodine complex of gram stain

- Gr- bacterium lose crystal violet-iodine complex

Some bacteria naturally lack cell wall:

Mycoplasma

- bacterium causes mild pneumonia

- have no cell wall, antimicrobial directed towards cell wall ineffective

- sterols in membrane account for strength of membrane

Bacteria in Domain Archaea

- have a wide variety of cell wall types

- none contain PTG but rather pseudoPTG

Binds proteins involved in cell wall synthesis.

Prevents cross-linking of glycan chains by tetrapeptides.

More effective against Gr+ bacterium:

- due to increased concentration of PTG

- Penicillin derivatives produced to protect against Gr-

Produced in many body fluids including tears and saliva ie natural way.

Breaks bonds linking NAG and NAM and destroys structural integrity of cell wall.

Enzyme often used in lab to remove PTG layer from bacteria:

- produces protoplast in G+ bacteria

- produces spheroplast in G- bacteria

Capsules and Slime Layer

General Function:

- protection ~ protects bacteria from host defenses

- attachment ~ enables bacteria to adhere to specific surfaces

Distinct gelatinous layer

Slime layer is irregular diffuse layer

Chemical composition of capsules and slime layers varies depending on bacterial species, but most are made of polysaccharide. Referred to as glycocalyx (sugar shell).

Long protein structure 

Responsible for motility, use propeller like movements to push bacteria

Can rotate more than 100,000 revolutions per minute (82 mph)

ccw: forward movement, run

cw: tumble

Some are important in bacterial pathogenesis 

Ex. H. pylori penetration through mucous coat; major cause of stomach ulcers/cancer

Three Basic Parts:

Filament ~ extends to exterior, made of proteins called flagellin

Hook ~ connects filament to cell 

Basal Body ~ anchors flagellum into cell wall

Flagella are rotary motors comprising a number of protein rings embedded in the cell wall. These molecular motors are powered by protein  motive force. 

Flagellin monomers self assemble into a left-handed helix - forming hollow tubular filament structure. 

New monomers travel down tube and assemble at distal end of filament. 

Motile through sensing chemicals

If chemical compound is nutrient, it acts as attractant.

If compound is toxic, it acts as repellant. 

Attractant or repellant bind to surface receptors in bacterial membrane.

Binding of specific receptors initiates cascade of intracellular signaling that turns motor proteins. 

Monotrichous: one strand

Lophotrichous: tuft on one end

Amphitrichous: one strand on each end

Peritrichous: everywhere

Considerably shorter and thinner than flagella

Composed of protein subunits called pilin

Function: 

- attachment (fimbre)

- movement

- conjugation ~ mechanism of DNA transfer

Hairlike appendage found on surface of many bacteria 

Primarily composed of oligomeric pilin proteins

Adherence to sufaces: 

External termini of the pili adhere to a solid substrate, either the surface to which the bacteria are attached or to other bacteria, and subsequent pilus contraction pulls the bacteria forward, like a grappling hook.

Twitching motility:

Movement is typically jerky, distinct from other forms of bacterial motility.