part 1 - holy family catholic...
TRANSCRIPT
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Microscopes (Ch. 6)
PART 1
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Dead White Men Who Discovered (and were made of) Cells:
Anton Van Leeuwenhoek Robert Hooke
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History of Cells
Robert Hooke - Observed
cells in cork.
Coined the term "cells” in
1665.
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History of Cells
1833 - Robert Brown, discovered the nucleus.
1838 - M.J. Schleiden, all plants are made of cells.
1839 - T. Schwann, all animals are made of cells.
1840 - J.E. Purkinje, coined the term “protoplasm”.
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Cell Theory
All living matter is composed
of one or more cells.
The cell is the structural and
functional unit of life.
All cells come from pre-
existing cells
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Light Microscopy
TECHNIQUE RESULTS
Brightfield (unstained specimen).
Passes light directly through specimen.
Unless cell is naturally pigmented or
artificially stained, image has little
contrast. [Parts (a)–(d) show a
human cheek epithelial cell.]
(a)
Brightfield (stained specimen). Staining
with various dyes enhances contrast, but
most staining procedures require that cells
be fixed (preserved).
(b)
Phase-contrast. Enhances contrast
in unstained cells by amplifying
variations in density within specimen;
especially useful for examining living,
unpigmented cells.
(c)
50 µm
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Differential-interference-contrast (Nomarski).
Like phase-contrast microscopy, it uses optical
modifications to exaggerate differences in
density, making the image appear almost 3D.
Fluorescence. Shows the locations of specific
molecules in the cell by tagging the molecules
with fluorescent dyes or antibodies. These
fluorescent substances absorb ultraviolet
radiation and emit visible light, as shown
here in a cell from an artery.
Confocal. Uses lasers and special optics for
“optical sectioning” of fluorescently-stained
specimens. Only a single plane of focus is
illuminated; out-of-focus fluorescence above
and below the plane is subtracted by a computer.
A sharp image results, as seen in stained nervous
tissue (top), where nerve cells are green, support
cells are red, and regions of overlap are yellow. A
standard fluorescence micrograph (bottom) of this
relatively thick tissue is blurry.
50 µm
50 µm
(d)
(e)
(f)
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Electron Microscopy
TECHNIQUE RESULTS
Scanning electron micro-
scopy (SEM). Micrographs taken
with a scanning electron micro-
scope show a 3D image of the
surface of a specimen. This SEM
shows the surface of a cell from a
rabbit trachea (windpipe) covered
with motile organelles called cilia.
Beating of the cilia helps move
inhaled debris upward toward
the throat.
(a)
Transmission electron micro-
scopy (TEM). A transmission electron
microscope profiles a thin section of a
specimen. Here we see a section through
a tracheal cell, revealing its ultrastructure.
In preparing the TEM, some cilia were cut
along their lengths, creating longitudinal
sections, while other cilia were cut straight
across, creating cross sections.
(b)
Cilia 1 µm
Longitudinal section of
cilium
Cross section of cilium
1 µm
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Cell Fractionation APPLICATION
Cell fractionation is used to isolate
(fractionate) cell components, based on
size and density.
TECHNIQUE
First, cells are homogenized in a blender to
break them up. The resulting mixture (cell
homogenate) is then centrifuged at various
speeds and durations to fractionate the cell
components, forming a series of pellets.
Tissue
cells
Homogenization
Homogenate 1000 g
(1000 times the
force of gravity)
10 min Differential centrifugation
Supernatant poured
into next tube
20,000 g
20 min
Pellet rich in
nuclei and
cellular debris
Pellet rich in
mitochondria
(and chloro-
plasts if cells
are from a
plant)
Pellet rich in
“microsomes”
(pieces of
plasma mem-
branes and
cells’ internal
membranes)
Pellet rich in
ribosomes
150,000 g
3 hr
80,000 g
60 min RESULTS
In the original experiments, the researchers
used microscopy to identify the organelles in
each pellet, establishing a baseline for further
experiments. In the next series of
experiments, researchers used biochemical
methods to determine the metabolic
functions associated with each type of
organelle.
Researchers currently use cell fractionation
to isolate particular organelles in order to
study further details of their function.
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Why Cells Are So Small: The SA:V Ratio Surface area increases while
total volume remains constant
5
1 1
Total surface area
(height width
number of sides
number of boxes)
Total volume
(height width length
number of boxes)
Surface-to-volume
ratio
(surface area volume)
6
1
6
150
125
12
750
125
6
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Prokaryote
bacteria cells Types of cells
Eukaryote
animal cells
- no organelles
- organelles
Eukaryote
plant cells
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Why organelles? • Specialized structures
– specialized functions
• Containers
– Compartments = different local environments
• pH, concentration differences
– distinct & incompatible functions
• lysosome & its digestive enzymes
• Membranes as sites for chemical reactions
– Unique lipids & proteins
– embedded enzymes & reaction centers
• chloroplasts & mitochondria
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Proteins do all the work!
cells DNA
proteins
organism Repeat after me…
Proteins do all the work!
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Cell functions
• Building proteins
– copy DNA
– DNA -> RNA
– build proteins
– process proteins
• Folding, modifying
–Remove amino acids
–Add molecules (e.g. glycoproteins)
– address & transport proteins
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Protein Synthesis • Organelles involved
– nucleus
– ribosomes
– endoplasmic reticulum (ER)
– Golgi apparatus
– vesicles
nucleus ribosome ER Golgi
apparatus vesicles
The Protein Assembly Line
The Endomembrane System
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Cell Wall
Nonliving jacket that
surrounds some cells.
Found in:
Plants
Prokaryotes
Fungi
Some Protists
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Plant Cell Walls
All plant cells have a Primary
Cell Wall.
Some cells will develop a
Secondary Cell Wall.
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