Prokaryotic Structures

Species and Subspecies

-Common definition of species used for animals (can produce viable offspring only when it mates with others of its own kind) does not work for bacteria -Bacteria do not exhibit a typical mode of sexual reproduction -For bacteria - a species is a collection of bacterial cells, all of which share an overall similar pattern of traits -Individual members of a bacterial species can show variations Subspecies, strain, or type- bacteria of the same species that have differing characteristics

PMF: Proton motive force

-Created by proton pumps -respiratory chain (uses energy (ΔG) in redox reactions -bacteriorhodopsin (uses light energy) -and used as H+ reenter the cell by flagella for transport to make ATP

Archaea

-Domain Archaea -Prokaryotic type of cells -Share many bacterial characteristics -How they differ from other cell types: Certain genetic sequences are found only in their rRNA Unique membrane lipids and cell wall construction (pseudoPG, proteins) -Many are found in extreme environments: Hyperthermophiles, Extreme halophiles, etc. -Important non-pathogens: Methane producers, etc.

Classification Systems in the Prokaryotae

-One of the original classification systems - shape, variations in arrangement, growth characteristics, and habitat -Definitive published source for bacterial classification: Bergey's Manual Since 1923 Early classification- the phenotypic traits of bacteria Current version- combines phenotypic information with rRNA sequencing

Flagellar Stain

-Special Stain -Determine: Presence Number Location -Stains used: Carbolfuscin Pararosanaline With mordants

Peptidoglycan Cell Wall 2

-The glycan portion of peptidoglycan is composed of a repeating disaccharide: N-acetyl glycosamine (G) N-acetyl muramic acid (M) -The peptide portion of peptidoglycan is composed of two short polypeptides: one attaches to the sugar, N-acetyl muramic acid; and one bridges between two adjacent glycan chains

How are Prokaryotes Different from Eukaryotes?

-The way their DNA is packaged No nucleus Not wrapped around histones -The makeup of their cell wall Bacteria- peptidoglycan Archae- tough and made of other chemicals, distinct to them -Their internal structures No complex, membrane-bound organelles

Flagellum

Bacterial locomotion Made of flagellin and other structural proteins Electric motor Rotates rapidly Many are reversible Propels the cell through its environment

Bacterial Motility 1

Chemotaxis- positive and negative; based on the direction of flagellar rotation Attractants and repellents Phototaxis Move by Runs: flagella in bundle Tumbles: flagella spinning in opposite direction are disarrayed

Glycocalyx

Commonly polysaccharides (carbohydrates) A few are polypeptides Differ among bacteria in thickness and organization: Slime layers and Capsules Protects the cell: Used to avoid phagocytosis - important for pathogenesis Sometimes helps the cell adhere to the environment (Biofilms, biofouling) Potential target for antimicrobial agents???

Plasmids

Composition DNA Circular Double stranded Independent replication 5-100 genes 1-700 copies in cell Function Types R plasmids: AB resistance F plasmids: Fertility Protein synthesis Unique proteins Exotoxins Endotoxins

The Cytoplasm

Contains the DNA in the nucleoid 70%-80% water; Gelatinous solution Many soluble proteins are present Carbohydrates and other intermediates are abundant This is the site of nearly all chemical reactions Bacteria have a cytoskeleton (long polymers of actin; contribute to cell shape), but it operates differently than in eukaryotes Some bacteria lay down nutrients in inclusion bodies (non-membrane bound granules) during periods of nutrient abundance. Serve as a storehouse when nutrients become depleted: Volutin - P storage; Polyhydroxybutyrate - Carbon storage

The Nucleoid

Contains the genetic material - DNA No nuclear membrane Single circular chromosome 500,000-10,000,000 nt Haploid Plasmids - double-stranded circles of DNA; Often confer protective traits such as drug resistance or the production of toxins and enzymes Chromosome + Plasmids = Genome The DNA is in close proximity to the cytoplasm and ribosomes.

Structure of the endospore

Core: DNA + small acid soluble proteins (SASP) + dipicolinic acid (binds Ca++) Cortex: special peptidoglycan (fewer side chains) - loose and expansile Coat: many proteins - very dense - protects against dehydration and UV and chemical damage

Work on new (2013) antibiotic to block secretion of capsular polysaccharides

Cyclic polysaccharide blocks transport channel (Wza) used to secrete capsule material. Allows phagocytes to recognize and kill bacteria more effectively. Hagen Bayley

Bacterial Nanowires

Electron transfer between cells

Flagellum Structure

Filament Flagellin chains in helix Hollow core for repair H protein antigen Hook Protein coupling L or curved shape Function: rotation Basal Body Function: anchor Central Protein Rod Ringed protein structures 4 rings for Gram Negative 2 rings for Gram positive

Prokaryotic Appendages-II

Flagella - used for motility Fimbria: - Small, bristle-like fibers - Most contain protein - Used for attachment to surfaces (including infection - N. gonorrhoeae) Pili: - Elongate, rigid tubular structures - Made of the protein pilin - Found on gram-negative bacteria - Used in - conjugation (genetic exchange), F pili - electron transfer between cells, "nanowires"

Prokaryotic Appendages-III

Flagella - used for motility Fimbria: - Small, bristlelike fibers - Most contain protein - Used for attachment to surfaces (including infection - N. gonorrhoeae) Pili: - Elongate, rigid tubular structures - Made of the protein pilin - Found on gram-negative bacteria - Used in - conjugation (genetic exchange), F pili - "nanowires"

Prokaryotic Appendages-I

Flagella - used for motility Fimbria: - Small, bristlelike fibers - Most contain protein - Used for attachment to surfaces (including infection - N. gonorrhoeae) Pili: - Elongate, rigid tubular structures - Made of the protein pilin - Found on gram-negative bacteria - Used in - conjugation (genetic exchange), F pili - electron transfer between cells, "nanowires"

The Cell Envelope: The Boundary layer of Bacteria

Majority of bacteria have a cell envelope Lies outside of the cytoplasm Composed of two (gram-positive bacteria) or three (gram-negative bacteria) basic layers: Cell wall Cell membrane The outer membrane

Biofilm

Microbial community Attachment to surface of host tissue or other microbes Cell to cell attachment Production of extracellular polysaccharides Planktonic colonization

Acid-Fast Bacteria

Mycobacteria Contain peptidoglycan + mycolic acid (a wax) Include important pathogens M. tuberculosis M. leprae

Mycoplasma

Mycoplasma don't have the cell wall at all (sterols ) Resistant to many common antibiotics M. pneumoniae

Practical Considerations of Differences in Cell Envelope Structure

Outer membrane - an extra barrier in gram-negative bacteria Makes them impervious to some antimicrobial chemicals Generally more difficult to inhibit or kill than gram-positive bacteria Lipopolysaccharides (LPS) - Outer layer of the outer membrane; Lipid A (endotoxin)

Flagellar Arrangements

Polar arrangement: flagella attached at one or both ends of the cell Monotrichous - single flagellum Lophotrichous - small bunches or tufts of flagella emerging from the same site Amphitrichous - flagella at both poles of the bacteria Non-polar arrangement: Peritrichous

Peptidoglycan Cell Wall 1

Present in most bacteria Provides strong structural support Helps determine the shape of a bacterium Sugar backbone Protein side-chain Target of many antibiotics!

Endospore-Forming Bacteria

Sporulation is NOT a reproduction! -Endospore - inside the cell -These bacteria have a two-phase life cycle: 1. Phase one - Vegetative cell Metabolically active and growing Can be induced by the environment to undergo spore formation (sporulation) 2. Phase two - Endospore (Hardiest of all life forms) Withstand extremes in heat, drying, freezing, radiation, and chemicals -Medical aspect of sporulation

Gram Positive Cell

Thick peptidoglycan (20 to 80 nm) Teichoic and Lipoteichoic acids - unique! One membrane Periplasm

Bacterial Shapes

Three general shapes: -Coccus- roughly spherical -Bacillus- rod-shaped Coccobacillus- short and plump Vibrio- gently curved -Spirillum- curviform or spiral-shaped Pleomorphism- when cells of a single species vary to some extent in shape and size

Gram Negative Cell

Two membranes: Cell membrane Outer membrane Lipopolysaccharide - unique! Thin peptidoglycan (1 to 3 nm) Periplasm

Prokaryote Ribosome

Two subunits (30S and 50S) Total size is 70S* Made of RNA and protein Special type of RNA- ribosomal RNA (rRNA) Its job is to translate mRNA into proteins * S: Svedberg unit; sedimentation/ ultracentrifugation

Cytoplasmic (Cell) Membrane

Very thin (5-10 nm) Contain primarily phospholipids (phospholipid bilayer) and hydrophobic proteins Semi - fluid nature Functions: - Provides a site for energy reactions, nutrient processing, and synthesis - Regulates transport (selectively permeable membrane): - Aquaporins (open channels for water) allow free passage of water - Small non-polar solutes also pass freely - Polar molecules and ions do NOT pass freely, but require controlled gates to open - Large molecules do NOT pass freely - require large complex transporters - Secretion

Slime layer-

a loose shield that protects some bacteria from loss of water and nutrients

Ion separation results in motive gradients (proton motive force)

both a CHARGE and a CONCENTRATION difference

Capsule

when the glycocalyx is bound more tightly to the cell and is denser and thicker