Chapter 4:Cell Structure/Function

Compound Light MicroscopyCompound Light Microscopy

Compound Light MicroscopyCompound Light Microscopy•Magnification

•Resolution capacity to distinguish as separate 2 adjacent points. Max resoultion of light microscope is 0.2 micrometers (2 points closer than 0.2 apart appear as one)

•Refractive Index measure of speed at which light passes through a material (staining increases the difference between refractive indexes of specimen and the medium…so contrast is increased)

•Brightfield illumination

Some microorganisms are pigmented. Most are not.

Green algae

Purple phototrophic bacteria

StainingStaining• Basic dyes (positive ion colored)

Positive stains

• Acidic dyes (negative ion colored)

Negative stains

Steps in smear preparation and staining

The Gram Stain

(a differential stain)

Gram Stain…Positive cocci and Negative rods

Darkfield microscopyDarkfield microscopy(specimem appears light against a black (specimem appears light against a black background)background)(good for seeing motility and very small or thin (good for seeing motility and very small or thin microbes)microbes)

Phase ContrastPhase Contrast(enhances differences in refractive indexes of (enhances differences in refractive indexes of structures, so…yields increase contrast) (good for structures, so…yields increase contrast) (good for seeing internal structures of living cells)seeing internal structures of living cells)

DarkfieldPhase contrastBrightfield

Cyanobacteria stained with fluorescent dye

Three-Dimensional Three-Dimensional ImagingImaging

Differential Interference Differential Interference Contrast MicroscopyContrast Microscopy

Atomic Force Microscope (AFM)

Confocal Scanning Laser Confocal Scanning Laser MicroscopyMicroscopy

Electron MicroscopyElectron Microscopy

TEM Transmission Electron Microscopy

SEM Scanning Electron Microscopy

CELL SIZE

(an upper limit is imposed by surface to volume ratio)

Prokaryotes and Eukaryotes Prokaryotes and Eukaryotes comparedcompared

• Similarities– Genetic material– Cellular chemistry and metabolic pathways– Some structures and functions

Prokaryotes and Eukaryotes Prokaryotes and Eukaryotes comparedcompared

• Differences (compartmentalization)– Prokaryotes

• DNA NOT enclosed by membrane• No membrane-bound organelles• No histone proteins associated with DNA• Complex cell walls• Division by binary fission

– Eukaryotes• DNA with a nucleus• Membrane-bound organelles• Histone proteins• Cell walls absent or simple• Division by mitosis

BASIC SHAPES

•Coccus

•Rod

•Spiral

CELL STRUCTURESCELL STRUCTURES

Cytoplasmic MembraneCytoplasmic Membrane

•Phospholipid bilayer studded with proteins (Fluid Mosaic Model)

•Selectively permeable barrier

•Membrane strengthening agents

•Sterols in eukaryotes

•Hopanoids in some bacteria

•Archaea contain very different lipids than Eukarya and Bacteria

Transport across Transport across membranesmembranes

Passive processes

Diffusion/osmosis

Facilitated diffusion

Active processes

Cell WallCell Wall•Peptidoglycan

• A polysaccharide which is the major component of cell walls in bacteria

• Archaea cell walls do not contain peptidoglycan

• Structure: Polysaccharide chains (glycans) cross-linked by peptide chains of amino acids.

•Two subunits N-Acetylglucosamine (G) and N-Acetylmuramic acid (M)

Gram Positive Cell Wall•Thick layer peptidoglycan

•Teichoic acid

• Lipoteichoic acid

Gram Negative Cell wall• Outer Membrane

• LPS-lipopolysaccharide (Endotoxin)

• Porins

• Periplasm

Genetic MaterialGenetic Material

• Nucleoid = area of the cell in which the DNA is aggregated

• Single circular chromosome

• Haploid

• Plasmids

MotilityMotility

FlagellaFlagella

•Filament

•Hook

•Basal Body

Rotational movement of the flagella

Peritrichous Polar (monotrichous)

Polar (lophotrichous)

TaxisTaxis

• Phototaxis

• Chemotaxis

Positive taxis

Negative taxis

Phototaxis: Figure shows movement of an entire colony of bacteria toward a light source at the right of the photo (not shown)

RibosomesRibosomes

• Site of protein synthesis

• Some structural differences between prokaryotic and eukaryotic ribosomes

• A major site of attack for antibiotics

Surface StructuresSurface Structures

Fimbriae and PiliFimbriae and Pili

S-LayersS-Layers

A surface layer made of protein found in many bacteria

Capsules and Slime LayersCapsules and Slime Layers

Glycocalx – polysaccharide-containing material outside of the cell

Inclusions/Storage Inclusions/Storage Bodies/GranulesBodies/Granules

Function in storage of energy molecules or as a reservoir of structural building blocks

PHB (poly-B-hydroxybutric acid)PHB (poly-B-hydroxybutric acid)

A carbon/energy storage polymer

• Glycogen (energy storage)

• Metachromatic granules (inorganic phosphate reserves)

Sulfur Granules

Magnetosomes

Iron-oxide crystals which allow the bacteria to respond to a magnetic field

Gas VesiclesGas VesiclesSmall gas filled protein structures that function to confer bouyancy on cells

EM of gas vesicles

Cyanobacteria “bloom” on lake surface

EndosporesEndospores• Hardiest of all life forms

• For escape from unfavorable environmental conditions

• Germination = return to the vegetative state from the spore state

• NOT reproductive (1 cell forms 1 endospore which return to reform 1 cell)

Endosymbiont theory of Eukaryotic Endosymbiont theory of Eukaryotic evolutionevolution

Evidence in support of the hypothesis• Mitochondria and chloroplasts contain their own

DNA• They contain their own ribosomes which are

very similar to prokaryotes• They divide independent of the cell and by

binary fission• Size, etc. etc