Transcript Chapter 4: Microscopy and Cell Structure

Chapter 4: Microscopy and Cell Structure
Resolution
Limits to Resolving Power:
Refractive Index
Aberration: Early lenses were generally not homogenous glass
and had variable refractive index across their surface, leading to
distortion
Types of Microscopes
Brightfield
Phase Contrast
Light
Differential Interference Contrast (DIC or Namarski)
Darkfield
Fluorescence
Con-Focal
Transmission EM
Electron
Scanning EM
Atomic Force Microscopy (AFM)
Principal of DIC (Differential Interference Contrast)
OR
Phase Contrast microscopy
Highligts:
Edges & Surfaces of objects
Fluorescence Microscope Optic Train
Microscope Comparison (Lens Trains)
TEM vs. SEM
TEM
see internal structure
can go to very high resolution
--- down to about 5 nm directly (further with image
averaging technique)
--- down to about 0.2 nm (2 angstrom) with electron
crystallography
cannot see surface features separately
see entire thickness of sample
SEM
see surface features only
can do elemental analysis of scattered electrons
lower resolution than TEM (around 100-200 nm)
sample preparation more difficult (but generally fewer artifacts)
Atomic Force Microscopy (AFM)
Advantages:
Range of resolutions
Live specimens
Cost
Disadvantages:
Image quality
Time consuming
Prokaryotic Cell Structure
Cell Shape
Rod/Bacillus
Bent Rod/ Vibrio
Spirillum (rigid helical shaped cell)
Spirochete (flexible spiral cell, contains a flagellum between
the cytoplamic membrane and outer membrane)
“Multicellular” Prokaryotes
actinobacteria form extensive networks of filaments that are
all cytoplamically contiguous (although there is some
barrier to free movement of material)
filamentous cyanobacteria also form filaments, in some
cases with cellular specialization
Also keep in mind that most bacteria live in communities
Cell Division
Fission (generally symmetrical)
Budding (distinctly asymmetrical)
Fragmentation
Internal Structures
DNA
Bacterial Chromosome (one DS molecule, haploid)
Plasmids (replicate independently of chromosome)
Transformation
Horizontal
Conjugation
Transfer
Transduction
Ribosomes (60 S) rRNA & Protein, involved in translation
Linked transcription & translation common in prokaryotes
Gas vesicles
Surrounded by protein sheath, used for buoyancy
Storage particles (Store nutrients and essential elements)
Glycogen/ Starch
Poly-B-hydroxybutryic acid (PHB)