AETIOLOGY STUDY SHEETS FOR MIDTERM EXAM
LECTURE 2: MICROSCOPY AND LAB TECHNIQUES
Describe a compound light microscope?
Series of lenses and uses visible light as source of illumination
Examine very small specimens (fine detail)
Ground lenses: forms focused image that is many times larger than the specimen itself
Magnification is achieved by:
Light rays from illuminator (light source) pass through a condenser (has lenses that
direct the light rays through the specimen). Light rays pass through objective lenses
(lenses closest to the specimen) Image of the specimen is magnified by ocular lenses
What is total magnification?
Multiply the objective lens maginification (power) by the ocular lens magnification (power)
What is resolution?
Ability of the lenses to distinguish fine detail and structure
What are the uses for each type of microscope?
Examine live microorganisms that are either invisible in the ordinary light microscope
Cannot be stained by standard methods
Distorted by staining therefore characteristics cannot be identified
Phase Contrast microscope
Permits detailed examination of internal structures in living microorganisms
Differential Interference Contrast Microscope (DIC)
Similar to phase contrast
Uses differences in refractive indexes
Image appears three dimensional
Absorbs UV light and emits visible light Confocal Microscope
Laser scans each plane of specimen
Reconstruct three dimensional images
Evaluate cellular physiology by monitoring the distributions and concentrations of substances
such as ATP and calcium ions.
What is an electron microscope?
Uses electrons instead of light
What does TEM stand for?
Transmission Electron Microscopy
What is TEM used for?
Used for thin/foil specimens
What does SEM stand for?
Scanning Electron Microscopy
What is SEM used for?
Used for thick and bulky specimens
What is simple stains?
Aqueous or alcohol solution of a single basic dye
Purpose is to highlight the entire microorganism so that cellular shapes and basic structures are
Mordant: chemical that is added to the solution to intensify the stain (increases affinity of a
stain for a biological specimen + to coat structure in order to make it thicker and easier to see
What is differential stains?
React differently with different kinds of bacteria and thus can be used to distinguish them
Differential stains most used for bacteria are the Gram Stain and the acid-fast stain
What is Differential stains: Gram Stain?
Classifies bacteria as gram positive or gram negative
Gram positive bacteria: thick multilayer peptidoglycan walls + more sensitive to antibiotics such
as penicillin Gram negative bacteria: thin peptidoglycan cells walls + more resistant to antibiotics which
cannot permeate LPS layer
Important in treatment surgeries
What are special stains?
Negative stains are useful for capsules which are water soluble and may be dislodged during
What are endospore stains (special stains)?
What are flagella stains? (Special stains)?
What are the four steps in preparing a gram stain?
1. Heat fixed smear is covered with a basic purple dye,usually crystal violet (primary stain)
2. Purple dye is washed off, and the smear is covered with iodine (mordant). When iodine is
washed off both gram positive and gram negative bacteria appear dark violet or purple
3. Slide is washed with alcohol/alcohol acetone solution (decolorizing agent)which removes purple
from the cells of some species but not others
4. Alcohol is rinsed off and the slide is then stained with safranin (Red dye). Smear is washed again,
blotted dry and examined microscopically.
Define gram positive
Bacteria that retain the dark violet or purple color after the alcohol has attempted to decolorize
Define gram negative
Bacteria that lose the dark purple or violet color after decolorization
Define bacterial colonies
Population of cells arising from a single cell or spore or from a group of attatched cells
What is the streak plate method?
Isolation method most commonly used to get pure cultures
1. Sterile incolutaing loop dipped into mixed culture and streaked over small sections of
2. Loop flamed 3. Next section of agar streaked by picking up a small amount of bacteria from the
5. Bacteria is diluted out and grown in isolated colonies
LECTURE 3: PROKARYOTES AND EUKARYOTES
Compare between prokaryotes and eukaryotes?
One circular chromosome not in membrane Paired chromosome in nuclear membrane
No histones histones
No organelles organelles
Peptidoglycan cell walls Cell walls or membranes
Binary fission Mitotic spindle
What are the basic shapes of bacteria?
Pairs and Chains: diplococcic, streptococci, single bacillus,diplobacilli, streptobacilli,
coccobacillus, vibrio, spirillum, spirochete
Clusters: tetrad, sarcinae, staphylococci
Unusual shapes: star shaped stella , Square halo arcula
Describe bacterial structures
Outside cell wall
Composed of sticky polysaccharide or polypeptide
Neatly organized or unorganized and loose
Virulence factor (prevents phagocytosis +for attatchment)
Filaments with protein chains of flagellin
Attatched to protein hook
Basal body anchor to wall/membrane
Rotational propeller movement Axial Filaments
Found in sphirochetes
Spiral bundles of fibrils
Anchored at one end of a cell
Rotation produces movement
Fimbriae or Pili
used for attatchment rather than motility
thinner than flagella
present in almost all prokaryotes
prevents osmotic lysis
peptidoglycans ( disachharides linked by polypeptides)
Gram Positive Cell Walls
Gram Negative Cell Walls
no teichoic acids
thin structure enclosing cytoplasm
inside cell wall
Proteins (peripheral, integral, transmembrane)
Cytoplasm Inside plasma membrane
single circular dsDNA
extra chromosomal mobile genetic element
thousands of very small granular structures
site of protein synthesis
consists of protein and rRNA
Resistant to dessication, heat chemicals
Sporulation: endospore formation
Germination: Return to vegetative state
Describe the process of sporulation
1. Spore septum begins to isolate newly replicated DNA and a small portion of cytoplasm
2. Plasma membrane starts to surround DNA, cytoplasm and membrane isolated in step 1
3. Spore septum surrounds isolated portion, forming forespore
4. Peptidoglycan layer forms between membranes 5. Spore coat forms
6. Endospore is freed from cell
Describe the following Eukaryotic Cell structures:
Flagella and Cilia
Projections containing cytoplasm enclosed by plasma membrane
Anchored by basal body
Nine pairs of microtubules in ring
Two microtubules in center made of protein tubulin
Fungi – carbohydrate cell walls
Glucan & mannan
Peripheral, integral transmembrane proteins
Cytoplasm membrane: substance inside plasma and outside nucleaus
Cytosol: fluid portion of cytoplasm
Cytoskeleton: microfilaments, intermediate filaments, microtubules
Cytoplasmic streaming: movement of cytoplasm throughout cells
Nucleaus: contains chromosomes
ER: transport network
Golgi complex: membrane formation and secretion
Lysosomes: digestive enzymes
Vacuoles: brings food into cells and provides support Mitochondrian: cellular respiration
Peroxisome: oxidation of fatty acids ; destroys H2O2
Ribosome: protein synthesis
Centrosome: protein fibers and centrioles
Centriole: mitotic spindle formation
Nucleaus: double membrane
Nuclear envelope: DNA + histones
Nucleolus: Threadlike protein mass
Chromatin: coils into chromosomes
Nuclear pores: allows communication with cytoplasm
Extensive network of flattened membraneous sacs or tubules
2 distinct forms (Rough ER & Smooth ER)
Rough ER: continuous with nuclear membrane, studded with ribosomes, synthesized proteins
Smooth ER: extends from rough ER, synthesizes fats and steroids
Transport synthesized proteins from ER
Transfer vesicles modify and move proteins from ER
Secretory vesicles deliver proteins to plasma membrane for excretion
Appear throughtout cytoplasm
Large surface area for ATP production
Powerhouse of the cell
Contains 70S ribosome and DNA