Chapter 4: Cell Structure/Function

Compound 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

Staining 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 microscopy (specimem appears light against a black background) (good for seeing motility and very small or thin microbes) Phase Contrast (enhances differences in refractive indexes of structures, so…yields increase contrast) (good for seeing internal structures of living cells)

DarkfieldPhase contrastBrightfield

Cyanobacteria stained with fluorescent dye

Three-Dimensional Imaging

Differential Interference Contrast Microscopy

Atomic Force Microscope (AFM)

Confocal Scanning Laser Microscopy

Electron Microscopy

TEM Transmission Electron Microscopy

SEM Scanning Electron Microscopy

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

Prokaryotes and Eukaryotes compared Similarities –Genetic material –Cellular chemistry and metabolic pathways –Some structures and functions

Prokaryotes and Eukaryotes compared 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 STRUCTURES

Cytoplasmic 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 membranes Passive processes Diffusion/osmosis Facilitated diffusion Active processes

Cell 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 Material Nucleoid = area of the cell in which the DNA is aggregated Single circular chromosome Haploid Plasmids

Motility

Flagella Filament Hook Basal Body

Rotational movement of the flagella

Peritrichous Polar (monotrichous) Polar (lophotrichous)

Taxis 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)

Ribosomes Site of protein synthesis Some structural differences between prokaryotic and eukaryotic ribosomes A major site of attack for antibiotics

Surface Structures

Fimbriae and Pili

S-Layers A surface layer made of protein found in many bacteria

Capsules and Slime Layers Glycocalx – polysaccharide-containing material outside of the cell

Inclusions/Storage Bodies/Granules Function in storage of energy molecules or as a reservoir of structural building blocks

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 Vesicles Small gas filled protein structures that function to confer bouyancy on cells EM of gas vesicles  Cyanobacteria “bloom” on lake surface

Endospores 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 evolution 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