Microscopes provide
windows to the world of
the cell
Cellular Diversity
• The average adult has
nearly 100 trillion cells
• There are about 200
different types of cells
• Cells come in a variety
of shapes and sizes
• Cellular diversity
permits organization of
cells into more
complex tissues and
organs
History of the Microscope
• 1665, Robert Hooke described cells using
a light microscope
• Magnification vs resolution
• Highest magnification of l.m. = 1000x
• 1950, Electron microscope allowed
researchers to clearly identify organelles
• There are 2 types:
– Transmission
– Scanning
Transmission Electron
Microscope
(TEM)
• e- transmitted through
specimen are focused
• image magnified by
electromagnetic lenses to bend
trajectories of charged e– Used to study internal cell
structure
– Image is focused onto a viewing
screen/film
Scanning Electron
Microscope
(SEM)
• e- beam scans surface of
specimen that is coated with
a thin film of gold
• Beam excites secondary eon sample’s surface
• Secondary e- are collected
& focused on viewing
screen
– Useful for studying surface of
specimen
– SEM has great depth of field
& produces 3D image
SEM images
Disadvantages of Electron
microscopes
• Can usually only view dead cells because
of the elaborate preparation required
• May introduce structural artifacts
Cell
Fractionation
• Technique that
enables researchers
to isolate organelles
without destroying
their function
– Disrupted cells are
centrifuged to isolate
components of
different sizes,
densities, and
shapes
Surface area: volume ratio
Why do you cut up potatoes to boil them?
Place in order depending on which will dissolve fastest  slowest
•granulated sugar
•Powdered sugar
•Sugar cube
•Fine sugar
Cells
• Prokaryotic vs Eukaryotic
• Cell sizes (0.1-100um)
– What limits a cell from being too large?
– Too small?
• Eukaryotic cells have 1000x volume of
prokaryotic cells, but only 100x the surface
area. How can they compensate for the
small surface area to volume ratio?
Prokaryote
“before nucleus”
Eukaryote
“true nucleus”
A Generalized Cell
Cytoplasm
- all the cellular
contents between the
plasma membrane and
the nucleus
- cytosol - the fluid
portion, mostly water
*site of many chem. Rx.
- organelles subcellular structures
having characteristic
shapes and specific
functions
The cytoskeleton network of protein
filaments
throughout the
cytosol
-provides structural
support for the cell
-three types
according to
increasing size:
microfilaments
(cables),
intermediate
filaments (cables),
and microtubules
(support beams)
Resist
tension
Bearing
tension
Resist
compression
Organelles
• Centrosome located near
the nucleus,
consists of two
centrioles
Cilia and Flagella
Cilia - short, hair-like
projections from the cell
surface, move fluids along a
cell surface
Flagella - longer than cilia,
move an entire cell; ex.
sperm cell’s tail
Internal Membranes
• Partitions cell into compartments
• Have unique lipid & protein compositions
depending upon their specific fx.
• Participate in metabolic reactions
(enzymes)
Class I: membrane derived
• 1. Nuclear envelope - a
double membrane that
separates the nucleus
from the cytoplasm
– Nuclear pores numerous openings in
the nuclear envelope,
control movement of
substances between
nucleus and cytoplasm
– Nucleolus - spherical
body that produces
ribosomes
2. Endoplasmic reticulum - network of membranes in the shape of flattened sacs or
tubules
- Rough ER - connected to the nuclear envelope, a series of flattened sacs,
surface is studded with ribosomes, produces various proteins
-Smooth ER - a network of membrane tubules, does not have ribosomes,
synthesizes fatty acids and steroids, detoxifies certain drugs
•3. Golgi complex - consists of
3-20 flattened, membranous sacs
called cisternae
- modify, sort, and package
proteins for transport to different
destinations
- proteins are transported by
various vesicles
4. Vesicles
• Sacs made of
membrane
• Transport substances
throughout cell and
to/fro membrane
5. Vacuoles
• Food vacuole  formed
by phagocytosis (protists
& macrophages)
• Contractile vacuole 
pumps excess water from
cell (protozoans)
• Central vacuole 
enclosed by membrane
(tonoplast); stores organic
compounds, ions,
poisons, provides turgor
pressure (plants)
6. Lysosomes
• Sequesters destructive enzymes from cytosol
• Maintains optimum acidic environment for enzyme
function
http://highered.mcgraw-hill.com/sites/dl/free/0072437316/120060/ravenanimation.html
Peroxisome
• Bound by a single
membrane derived from
lipids w/i cell
• Contains enzymes that
transfer Hydrogen atoms
from various substrates to
oxygen (H O ).
• Contains catalase that
converts H O to water.
• Breaks down fatty acids
• Detoxification of alcohol &
other poisons (liver)
2
2
2
2
Class II: bacteria like organelles
(energy production)
Mitochondria - the
“powerhouses” of the cell
– Generate ATP
– More prevalent in
physiologically active cells:
muscles, liver and kidneys
– Inner and outer mitochondrial
membranes
– Cristae - the series of folds of
the inner membrane
– Matrix - the large central fluidfilled cavity
– Self-replicate during times of
increased cellular demand or
before cell division
Class III: Involved in Gene Expression