1. Concept: Cell Biology tools - microscopy & chemistry
The quality of an image depends on
Magnification, the ratio of an object’s image size to its real size
Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points
Contrast, visible differences in parts of the sample (can be enhanced by stains/markers)

2. -Electron Microscope 2 nm
Scale of Resolution
-Naked Eye .2 mm
-Light Microscope .2 mm
-Electron Microscope 2 nm
10 m
Human height
1 m
Length of some nerve and muscle cells
0.1 m
Unaided eye
Chicken egg
1 cm
Frog egg
1 mm
100 µm
Most plant and animal cells
Light microscope
10 µm
Nucleus
Most bacteria
1 µm
Mitochondrion
Figure 6.2 The size range of cells
Smallest bacteria
Electron microscope
100 nm
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms

3. Light Microscopy
In a light microscope (LM), visible light passes through a specimen and then through glass lenses, which magnify the image
Various techniques enhance contrast and enable cell components to be stained or labeled
Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by a Light Microscope

4. Viewing Techniques for: Imaging
Naked Eye
Light Microscope
Electron Microscope
TECHNIQUE
RESULTS
(a) Standard/Brightfield
(unstained specimen)
Imaging
50 µm
(b) Standard/Brightfield
(stained specimen)
Imaging w/ stain
(c) Phase-contrast
Imaging & density
The microscope manipulates optics to improve contrast between the structures
(d) Differential-interference-
contrast (Nomarski)
Imaging & optics
(e) Fluorescence
Imaging w/ Labeling
Figure 6.3a-d Light microscopy
50 µm
(f) Confocal
Imaging & focal planes
50 µm

5. Electron microscopy
Two basic types of electron microscopes (EMs) are used to study subcellular structures
Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a heavy metal stained specimen, providing images that look 3-D
Transmission electron microscopes (TEMs) focus a beam of electrons through a heavy metal stained specimen, used mainly to study the internal structure of cells

6. (b) Transmission electron
TECHNIQUE
RESULTS
Cilia
1 µm
(a) Scanning electron
microscopy (SEM)
SURFACE
Longitudinal
section of
cilium
Cross section
of cilium
1 µm
Figure 6.4 Electron microscopy
(b) Transmission electron
microscopy (TEM)
SECTION OR SLICE

7. Cell Fractionation
Cell fractionation takes cells apart and separates the major organelles from one another
Centrifuges fractionate cells into their component parts
Cell fractionation enables scientists to determine the functions of organelles
Biochemistry and cytology help correlate cell function with structure

8. Successive steps of centrifugation under different speeds (g forces)
TECHNIQUE
Homogenization
Tissue
cells
Homogenate
1,000 g
(1,000 times the
force of gravity)
10 min
Differential centrifugation
Supernatant poured
into next tube
20,000 g
20 min
Successive steps of centrifugation
under different speeds (g forces)
yields different sedimentaion
80,000 g
60 min
Pellet rich in
nuclei and
cellular debris
Figure 6.5 Cell fractionation
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloro-
plasts if cells
are from a plant)
Pellet rich in
“microsomes”
(pieces of plasma
membranes and
cells’ internal
membranes)
Pellet rich in
ribosomes