Microbiology Chapter 4- Prokaryotes

Distinguishing Characteristics- Prokaryotes ("Prenucleus")

1. DNA not enclosed w/in a membrane. Singular circularly arranged chromosome.
2. NOT associated with histones
3. Lack membrane-enclosed organelles
4. Cell walls almost always have complex polysaccharide peptidoglycan
5. Binary fission. (DNA copies, split into two)

Distinguishing Characteristics- Eukaryotes ("True Nucleus")

1. DNA is in nucleus and in multiple chromosomes. Separated from cytoplasm by a nuclear membrane.
2. DNA associated with proteins- Histones and Non-histones.
3. Membrane-enclosed organelles: Mitochondria, ER, Golgi Complex, Lysosomes and Chloroplasts.
4. If cell walls= simple!
5. Mitosis

Bacteria range in size from _____ in diameter and ______ in length.

0.2-2.0 micrometers -diameter
2-8 micrometers- length

What are the 3 possible shapes of bacteria?

Coccus: spherical
Bacillus: rod-shaped
Spiral

Cocci are usually ______ and are elongated and flattened on one side

Round

Cocci ______ to reproduce

divide!

After division of Cocci, cells can remain attached.
If they remain in pairs= ________
Remain in chainlike patterns= _______
Divide in 2 plains and remain in groups of 4 =___
Divide in 3 planes & remain in groups of 8=_____
Divide in many planes & form clusters=________

Pairs= diplococci
Patterns= streptococci
Groups of 4= tetrads
Groups of 8= sarcinae
Clusters= staphylococci

Bacilli appear as _______ and divide only across their short axis

single rods

Diplobacilli

Appear in pairs after division

Streptobacilli

Occur in chains

Coccobacilli

Oval, look very similar to coci

"Bacillus" has 2 meanings:

1. Bacterial shape
2. Specific genus

Vibrios

Bacteria that look like curved rods

Spirilla

Helical shape. Rigid bodies. Propeller-like external appandages (Flagella)

Spirochetes

Helical AND Flexible
Move by axial fillaments (resemble flagella but are internal)

In addition to the main 3 shapes, there are...

1. Stella: star-shaped
2. Haloarcula: rectangular, flat
3. Triangular

Shape is determined by ______

Heredity

Most bacteria are monomorphic, meaning that they...

maintain a single shape.

T/F: Environmental conditions can alter shape.

True!

Some bacteria are pleomorphic, meaning that they...

Can have many shapes

The typical structure of a Prokaryotic cell is made of what 3 components?

1. Structures external to the cell wall
2. The cell walll
3. Structures internal to the cell wall

Structures external to the cell wall include:

Glycocalyx
Flagella
Axial Fillaments
Pili
Fimbriae

Describe the Glycocalyx

-Substance secreted by prokaryotes on the surface.
-General term used for substances that surround cells
- is viscous (sticky)
-Gelatinous polymer
-Composed of polysaccharide OR polypeptide OR both
-Made inside the cell then secreted out

Something is a "Capsule" if...

-the substance is organized and firmly attached to the cell wall

The presence of a capsule can be detected by...

Negative staining

Something is a "Slime Layer" if...

-it is unorganized and loosely attached to cell wall

Some species of capsules contribute to ____ and protect _____

-bacterial virulence
-pathogenic bacteria from phagocytosis by the cells of the host

Glycocalyx is a very important component of _____

Biofilms

Extracellular Polymeric Substance

Glycocalyx that helps cells in a biofilm attach to their target environment and to each other.
-protects cells within it
-facilitates communication between the cells
-enables cell survival by attaching to various surfaces

Glycocalyx can protect a cell against...

Dehydration and viscosity can prevent the nutrients from leaving the cell

Flagella

-long, filamentous appendages that propel bacteria

Bacteria without Flagella are called:

Atrichous

2 types of Flagella:

1. Peritichous: distributed over the entire cell
2. Polar: @ one or both poles/ends of cells

If the flagella are POLAR, they can be...

1. Monotrichous: single flagellum @ one pole
2. Lophotrichous: a tuft of flagella from one pole
3. Amphitichous: Flagella @ both poles

What are the 3 basic parts of Flagella?

1. Filament
2. Hook
3. Basal Body

Filament

-long, outermost region
-constant in diameter
-contains globular protien flagella in chains that intertwine/form a helix around hollow core
-not covered by membrane/sheath
-attached to slightly wider HOOK

Basal Body

-anchors flagellum to the cell wall and plasma membrane
-composed of a small central rod inserted in a series of rings

Gram Negative Basal Body

-2 pairs of rings
1. outer pair anchored to portions of cell wall
2. inner pair anchored to plasma membrane

Gram Positive Basal Body

Only inner pair is present

Each flagellum is semirigid and helical, and move by ________.

Rotation from the basal body.

**Rotation is either clockwise or counterclockwise

Bacterial cells can alter the ____ & _____ of rotation of flagella, which makes it capable of patterns of ______.

-Speed and Direction
-Motility

Motility

-Ability of an organism to move by itself
-Enables bacterium to move toward a favorable environment or away from bad.

Movement in one direction for any length of time =

"Run" or "Swim"

"Runs are interrupted by random changes called:

"Tumbles"

"Tumbles" are caused by

Reversal of flagella rotation

Taxis

The movement of bacterium toward/away from particular stimulus

2 types of stimuli that spur Taxis

1.Chemotaxis: chemicals
2. Phototaxis: light

Motile bacteria have receptors to pick up chemical stimuli such as _______, and signals pass the information to flagella.

Oxygen
Ribose
Galactose

2 types of signals

1. Positive Chemotactic Signal= "Attractant"- move toward stimulus with many runs, few tumbles

2. Negative Chemotactic Signal= "Repellent"- frequency of tumbles increases as bacteria move away

H Antigen

Flagellar protein. Useful for distinguishing among serovars- variations within a species of gram-negative bacteria.

Axial Fillaments

-Anchored at one end of spirochete
-structure similar to flagella
-movement similar to corkscrew: enables bacterium to move more effectively through bodily fluids

Spirochetes

-unique structure and motility
-move by axial fillaments or endoflagella
-bundles fibrils @ ends of the cell beneath an outer sheath/spiral around the cell

__________ bacteria have hairlike appendages that are shorter, straighter, thinner than flagella and are used for attachment/trasnfer of DNA

Gram Negative

Fimbriae

-Can occur @ poles or evenly distributed over entire surface of cell
-# from 2-hundreds per cell
-adhere to each other/surfaces
-involved in forming biofilms
-help bacteria adhere to epithelial surfaces in body

Pili

-longer than fimbriae
-small # in cell
-involved in motility and DNA transfer (twitching and gliding motility)
-used to bring bacteria together to allow DNA transfer (conjugation) = Conjugation Pili

Twitching Motility

Pili extend by addition of subunits of pilun, make contact with surface, then retracts as subunits are dissembled.
-"Gripping Hook Model": results in short, jerky movements

Gliding Motility

Smooth, gliding movement of myxobacteria.
-allows microbes to travel in environments with low water content (biofilms and soil)

Cell Wall

-Complex, semirigid structure repsonsible for shape of the cell
-surrounds plasma membrane and protects it from adverse changes.
-almost all prokaryotes have cell walls
-helps maintain shape/serves as point of anchorage for flagella
-contributes to ability of species to cause disease
-site of action for antibiotics

Major Function of the Cell Wall

To prevent bacterial cells from rupturing when water pressure is greater than it is outside the cell.

The cell wall is composed of a macromolecule network called:

Peptidoglycan

Peptidoglycan

-components of it are assembled in the cell wall
-forms "backbone" by alternating NAM and NAH molecules in linked rows
-Adjacent rows are linked by polypeptides
-4 amino acids are attached to the "backbone" and alternate in D and L patterns.

_________ interacts with the amino acid patterns by peptide cross-bridges.

Penicilin

Peptide Cross-Bridges...

Weakens cell wall so the cell undergoes lysis.

Lysis

Destruction caused by rupture of plasma membrane and loss of cytoplasm.

Gram Positive Cell Walls

-many layers of peptidoglycan- thick, rigid structure
-contain teichoic acids (primary alcohols)

2 classes of Teichoic Acids

1.Lipoteichoic: spans peptidoglycan and is linked to plasma membrane
2. Wall Teichoic: linked to peptidoglycan layer

Negatively charged Teichoic Acids

May bond and regulate movement of cations

Teichoic Acids are involved in...

-Cell growth
-Preventing wall breakdown
-Preventing cell lysis

Cell walls of Gram Positive Streptococchi are covered with...

-Polysaccharides
-grouped into medically significant types

Gram Negative Cell Walls

-Thin layer of peptidoglycan and an outer membrane
-Peptidoglycan is bonded to lipoproteins in outer membrane
-also in the periplasm (gel-like fluid b/w outer and plasma membrane)
-do not contain Teichoic Acids
-Low amounts of Peptidoglycan = high susceptibility to mechanical breakage

Outer membrane of Gram Negative Cell Walls contains ______

Lipopolysaccharides (LPS)

Specialized functions of the Outer Wall

-Strong (-) charge = ability to evade phagocytosis
-provides barrier to certain antibiotics (penicillin), digestive enzymes (lysozome), detergents, heavy metals, bile salts and some dyes.

The outer wall is slightly permeable because...

Porins: proteins that form channels and permit the passage of molecules (nucleotides. disaccharides, peptides, amino acids, vitamin B12 and Fe)

LPS of the outer membrane

-large complex molecule
-3 components:
1. Lipid A
2. Core polysaccharide
3. O polysaccharide

Lipid A

-Lipid portion of LPS
-embedded in top layer of outer membrane
-released by gram-negative bacteria when they die (functions as an endotoxin)
-repsonsible for symptoms associated with infections by gram negative bacteria (fever, shock, etc)

Core Polysaccharide

-Attached to Lipid A, contains unusual sugars
-structural role = to provide stability

O Polysaccharide

-extends outward from core p.
-composed of sugar molecules
-functions as an antigen
-useful for distinguishing species of gram-negative bacteria

The Gram Stain mechanism is based on...

Differences in the structure of the cell walls of Gram +/- and how they react to the reagents

__________ stains both +/- purple b/c the dye enters the cytoplasm of both cells.

Crystal Violet

Iodine (mordant) causes

Crystals to form

Alcohol Wash and Gram +

Dehydrates the peptidoglycan, making it impermeable to the c.violet-iodine

Alcohol wash and Gram -

Dissolves the outer membrance and leaves holes in peptidoglycan layer.

-C. violet-iodine layer diffuses

Atypical Cell Walls

-No walls or very little material

Archaea

-lack walls or have walls that contain polysaccharides/proteins
-NOT peptidoglycan

Enzymatic Treatment

-Chemicals in cell wall usually prevent harm
-Can be damaged by exposure to Lysozyme

Lysozyme

-digestive enzyme
-occurs naturally in some eukaryotic cells
- in TEARS, mucus and saliva
-active on the major cell wall components of most Gram + bacteria
**Catalyzes hydrolysis of the bonds b/w the sugars in the repeating disaccharide "backbone" or peptidoglycan
-completely destroys gram + wall

If lysis does not occur, the contents of the cell may remain surrounded by the plasma
membrane= ?

Protoplast

Those in genus Proteus- can lose their cell walls and swell into irregularly shaped cells =

L Forms

L Forms

-may form spontaneously or in repsonse to penicillin
-can live/divide repeatedly

When Lysozyme is applied to Gram - walls...

-wall is not destroyed to same extent as +
-Part of outer membrane remains

After Lysozyme, the cellular contents, plasma membrane, and remaining outer wall =

Spheroplast

Protoplasts and Spheroplasts ______ in pure water or very dilute salt/sugar sol'ns b/c the water molecules rapidly move into/enlarge the cell =

Osmotic Lysis

Plasma Membrane

-thin structure lying inside the cell wall and enclosing the cytoplasm
-consists primarily of phospholipids
-e- micrographs- look like 2-layered structures
-phospholipid molecules are arranged in 2 parallel rows = lipid bilayer

Most important function of Plasma Membrane

Serve as a selective barrier through which materials enter/exit the cell

**Selective permeability

Movement Across Membranes includes...

1. Passive Processes
2. Osmosis

Passive Processes: Simple Diffusion

Net movement of molecules/ions from high concen. to low concen. until ions/molecules are evenly distributed
-Cell does NOT expend energy
***Equillibrium

Passive Processes: Facilitated Diffusion

Proteins function as channels/carriers that facilitate movement of ions across membranes.
-Cell does NOT expend energy
-Uses transporters

Osmosis

-Net movement of solvent molecules across a selectively permeable membrane. High to low concen.
-Chief Solvent = Water!

Osmotic Pressure

Pressure required to prevent movement of pure water into a solution containing some solutes

3 types of osmotic solutions

1. isotonic
2. hypotonic
3. hypertonic