Microbil Cell Structure And Function Flashcards
Many different types of light microscopy:
• Bright-field
• Phase-contrast • Dark-field
• Fluorescence
the ability to make an object larger
Magnification
the ability to distinguish two adjacent objects as separate and distinct
Resolution
Specimens are visualized because of differences in contrast (density) between specimen and surroundings
Bright-field scope
_____ improves contrast
Staining
____ are organic compounds that bind to specific
cellular materials
Dyes
Examples of common stains
methylene blue, safranin, and crystal violet
_______ separate bacteria into groups
Differential stains
_____ is widely used in microbiology
Gram stain
Bacteria can be divided into two major groups:
gram-positive and gram-negative
Gram-positive bacteria appear _____ and gram-negative bacteria appear ______ after staining
Purple, red
• Invented in 1936 by Frits Zernike
• Phase ring amplifies differences in the refractive index of cell and surroundings
• Improves the contrast of a sample without the use of a stain
• Allows for the visualization of live samples
• Resulting image is dark cells on a light background
Phase-contrast microscopy
• Light reaches the specimen from the sides
• Light reaching the lens has been scattered by specimen
• Image appears light on a dark background
• Excellent for observing motility
• Dark-field microscopy
• Used to visualize specimens that fluoresce
• Emit light of one color when illuminated with another color of light
Fluorescence microscopy
- Specific on staining DNA: A-T rich region
- Can stain both live (less efficient) and fixed cells - Excited by an ultraviolet light (358nm) emit blue
color (461nm).
DAPI
Two types of electron microscopes:
• Transmission electron microscopes (TEM)
• Scanning electron microscopes (SEM)
• Electromagnets function as lenses
• System operates in a vacuum
• High magnification and resolution (0.2 nm)
• Enables visualization of structures at the molecular level
• Specimen must be very thin (20–60 nm) and be stained (osmic acid,permanganate, uranium lanthium or lead
salts)
Transmission electron microscopy (TEM)
• Specimen is coated with a thin film of heavy metal (e.g., gold)
• An electron beam scans the object
• Scattered electrons are collected by a detector, and an image is produced
• Even very large specimens can be observed • Magnification range of 15✕–100,000✕
Scanning electron microscopy (SEM)
cell shape
Morphology
Major cell morphologies
Coccus (pl. cocci)
Rod
Spirillum
spherical or ovoid
Coccus (pl. cocci)
cylindrical shape
Rod
spiral shape
Spirillum
Cells with unusual shapes
Spirochetes, appendaged bacteria, and filamentous
bacteria
Size range for prokaryotes:
0.2 μm to >700 μm in diameter
Most cultured rod-shaped bacteria are between______ wide and_____ long
0.5 and 4.0 μm, < 15 μm
• Examples of very large prokaryotes
• Epulopiscium fishelsoni
• Thiomargarita namibiensis
Size range for eukaryotic cells:
10 to >200 μm in diameter
Size of Epulopiscium fishelsoni
(600um long, 75um wide)
Size of Thiomargarita namibiensis
(400 – 750um)
• Thin structure that surrounds the cell
• Vital barrier that separates cytoplasm from environment
• Highly selective permeable barrier; enables concentration of specific metabolites and excretion of waste products
Cytoplasmic membrane
Composition of membranes
