Morphology of Prokaryotic cells

• Prokaryotic cells in a variety of simple shapes

• Bacteria with similar shapes can share some characteristics

• some aggregate and live as multi-cellular communities

• most common shapes

  • Coccus-spherical

  • Rod-cydrical

The Prokaryotic cell

Extracellular

• cell Wall

• Capsules and slime layers

• filamentous appendages

Cell Boundary

• cytoplasmic membrane

Intracellular

• DNA

• Cytoskeleton

• Gas vesicles

• Granules

• Ribosomes

• Endospores

Bacterial Cell wall

• Ridgid, determins shape of the organism

• prevents bursting

• not all species of bacteria have a cell wall

• Differences exist from the cell wall of Eukaryotes

Structure

• Rigidity due to peptidoglycans

Peptidoglycans

• only found in bacteria

• Alternating two major subunits (related to

• glucose) NAM and NAG

Structure

• Polypeptides

• tetra peptides (4amino.acid string)

• Peptide Chains provide cross-links between NAM Molecules

• The precise this happens varies between Gram-positive and Gram-negative

Gram Positive Cell wall

Thick peptidoglycan layer

• As many as 30 layers

• permeable

Teichoic acids

• chains of rubitol Phosphate or glycerol phosphate

• sugars and D-alanine can attach

• stick out above peptidoglycan

  • can Stain

Gram Negative Cell Wall

• more complex

• Thin peptidoglycan layer

outer membrane

• unlive other membranes in Nature

  • outside of the peptidoglycan layer

  • lipid bilayer with proteins

  • most molecules can't pass

    • less susceptible to antibiotics

  • Porins-Protiens that allow small molecules to pass

  • outside layer made up of lipopolysaccharides

Periplasm

• between outer and cytoplasmic membranes

  • contains secreted proteins waiting to be moved across the outer membrane

Liposaccharide

• when purified and injected into host, causes bacterial infection

  • symptoms are the same for LPs molecules from different bacteria

    • Endotoxin

  • LPs Molecule

  • Lipid A

    • Part of IPS in the Lipid bilayer

    • causes endotoxin symptoms

  • O-Specific polysaccharide

    • Part of LPs away from the membrane

    • variation can be used to Identify some species and strains

Antibacterial Substances Target Peptidoglycan

• peptidoglycan makes a good target since it is unique to bacteria

  • weakened cell walls can lyse

• Penicillin interferes with peptidoglycan Synthesis

  • prevents cross-linking of adjacent glycan chains

  • more effective against Gram-positive bacteria than Gram-negative bacteria

    • the outer membrane of Gram-negatives blocks access

    • Derivatives have been developed that can cross

• Lysosome breaks bonds linking the glycan chain

  • enzyme found in tears, Saliva, and other bodily fluids

  • Destroys structural integrity of peptidoglycan molecule

Bacteria with no cell wall

• Highly Variable Shape

• Not affected by penicillin in or lysosome

• Stronger membrane

  • EX Mycoplasma species

Archea Cell Wall

• lots of variety

• mostly due to the requirements of each extreme environment

• no peptidoglycan

• use of pseudo peptidoglycans

Bacteria Capsules and Slime Layers

• Glycocalyx- a coating of hydrated gly corporations and glycolipids that come out of and cover membranes in cells and bacteria that serve as protection

• layer for protection or attachment

  • capsule: gelatin-like, polysaccharides are firmly attached to the cell wall

  • slime layer: Irregular and diffuse, polysaccharides loosely attached

• make conies appear Shiney

Filamentous Protien Appendages

• Some bacteria have appendages

• not essental but do confer some advantages

• most are anchored in cell membrane

  • Flagella

  • Pili

Flagella

• long, made of potion

• responsible for most bacterial movement

• uses proton motive force for energy

• works very hard

• can be needed for a bacteria to cause disease

• Different types of arrangements

Structure

Filament

• made of flagellin protiens

  • Extends into environment

HOOK

• connect filament to cell surface

  • Basal body

  • Anchors the flagellum to the cell wall and y toplasmic membrane

Uses

• motility as a response to some stimuli

  • Chemotaxis

  • Phototaxis

  • Arestaxis

  • Magnetotaxis

  • Thermotaxis

• cell moves via a series of runs and tumbles

• can move randomly when there is no concentration gradient of attractment or repellent

• when a cell senses it is moving toward an attractant it tumbles less frequently so the runs in the direction of the attractant are longer

Pili and Fimbriae

• Shorter and thinner then flagella but same basic Structure

• functions differently from flagella

uses

Fimbriae

• short attachment pili for specific surfaces, colonization

Sex Pili

• uses as anchor between two bacteria during special DNA exchange

Motility

• Twitching and gliding usually for a population of cells

The Prokaryotic Cell

Extracellular

• cell wall

  • capsules and slime layers

  • filamentous appendages

Cell Boundary

• cytoplasmic membrane

Intracellular

• DNA

  • Cytoskeleton

  • Gas Vesicles

  • Granules

  • Ribosome

  • Endospore

Cytoplasmic Membrane

• Defines the boundary of the cell

• surrounds cytoplasm

• Semipermeable /selectively permeable

• Phospholipid bilayer with embedded protiens

  • Hydrophilic head - glycerol and phosphate group

  • Hydrophobic tai l- two fatty acid chains

How do things get across?

• cytoplasmic membranes are selectively permeable. meaning some molecules pass through freely while others have to be actively moved across the membrane

methods used

• simple diffusion

  • osmosis

• Facilitated diffusion

• Active transport

• secretion

Internal structures

DNA

Chromosome

• contains all the genetic information required by a cell

  • Single, circular, double-stranded DNA

    • packed tightly via binding protiens and supercoiling

  • Exists as a gel-like region - nucleoid

Plasmid

• Double stranded, supercoiled DNA

  • Small

    • 0.1% -10% of the chromosome

  • can hold a few or hundreds of genes

  • not required for life but confers some sort of selective advantage Cie. antibiotic resistance)

  • can be transferred between bacteria

  • Located in the Cytoplasm

  • important when using bacteria for research is a model organism

Ribosomes

• site for amino acid joining for protien production

  • made of RNA(rRNA) and ribosomal potions

  • composed of two subunits a large and small

    • 70s ribosome

      • 50s large subunit

      • 30s small subunit

  • Prokaryotic us Eukaryotic

    • Prokaryotic ribosomes are smaller

    • The core rRNA and proteins are almost Identical between prokaryotes and eukaryotes

    • Differences that do not exist are. pharmaceutically exploited as a target for new antibiotics

Cytoskeleton

• originally thought prokaryotes lacked a Cytoskeleton

  • recent findings show bacterial proteins similar to Eukaryotic cytoskeletal protiens which may be involved in cell division and shape

Endospores

• Dormant bacterial cell

  • produced by certain bacteria in response to environmental stress (starvation)

  • resistant to extreme conditions

    • Heat

    • Toxins

    • UV irridation

    • Desiccation

  • Produced by a process called sporulation

  • not in the bacterial cell at all times

  • Endospores survive a long time and are hard to kill

    • some cause disease

      • botulism, gangrene, antrax, tetanus

Microscopes

Light

• uses visible light to observe objects and glass lenses to Magnify

• Magnifies 1000 fold

Electron

• uses electrons, electromagnetic lenses, and a fluorescent screen to visualize a specimen

• Magnifies 10,000 fold

Atomic force microscope

• can produce images of individual atoms on a surface

Principles of Light Microscopy

• light passes through the specimen and then a series of magnifying lenses

• The bright-field microscope is the most common type

• three key concepts

  • Magnification

  • Resolution

  • contrast

Magnification

• Apparent increase in Size

• modern compound microscopes have two lens types: objective and ocular

• Magnification is product of objective (4x, 10x, 40x, and 100x) and ocular lens (10x)

• condenser lens (between light course and specimen) focuses light on specimen, does not magnify

Resolution

• Resolving power or the ability to distinguish two objects that are very close together

• Defined as the minimum distance between two points at which those points can be observed as separate

• Depends on the quality and type of lens, a wavelength of light, Magnification, and specimen preparation

• the maximum resolving power of a light microscope is 0.2 micrometers

• Immersion Oil is used to displace air between the lens and Specimen when using a high-powered 100x objective

• has the same refractive index (a measure of the speed of light passing through a medium) as glass

• prevents refraction of light, keeps rays from opening in objective lense

Contrast

• Determines how easily cells can be seen

• Bacteria are mostly transparent against bright background

  • not much contrast between the bacteria and background making them difficult to see

• Stains are used to increase contrast

  • stains kill microbes, living cells can not be observed with this method

Electron microscopes

Transmission

• TEM-electrons through specimen

• observe fine detail of cell structure

• Elections directed at the Specimen will either pass through or be scatted depending on the density of that portion of the specimen

• Elaborate specimen preparation to improve image

  • thin sectioning

  • freeze fracturing and etching

Scanning

• SEM-electrons scan over specimen coated with metal

• produces 3D image

• used to observe the surface details of the cell

Microscopy Techniques

• most organisms are mostly transparent

• some are speedy-require immobilization

• Staining a specimen facilitates viewing through light microscopes

Types of Stains

• simple

• Differential

• special

• fluorescent dyes and tags

Simple Stains

• only uses one Stain

• a simple way to increase contrast

Basic Dyes

• positive Charge

• Attracted to negatively Charged cellular components

Acidic Dye

• Negative Charge

• colors the background to provide contrast (negative Staining)

Differential Stains

• muti-step process

• Distinguishes between groups of microorganisms

Gram Stain,

• used to distinguish between two major groups of microorganisms based on cell wall differences

Acid-fast

• Identifies microorganisms that don't reading take up Stain such as the genus mycobacterium- cause of tuberculosis and leprosay

Special Stains

• Capsule Stain

• Endsspone Stain

• Flagella Stain

Fluorescent Stain

• Dyes

  • specific and Universal

• Immunofluorescence

  • tag specific protiens