Transparency:
Features of cells visible using an electron microscope (1)
cell surface membrane
of upper cell
texture of cell wall
(in plant cells only)
cell wall
cell surface membrane
of lower cell
cytoplasm
plasmodesma
(25 nm wide)
micrograph of cell wall
granum
(with chlorophyll)
membrane
lipid (fat)
starch outer membrane of
grain chloroplast envelope
(lamella)
inner membrane of stroma
chloroplast envelope
micrograph of chloroplast (x 8000)
D. Ehrig, Brinkum
organelles_em
Transparency:
Features of cells visible using an electron microscope (2)
nucleolus
chromatin (= disorganized genetic material)
nuclear
pore
outer
inner
membrane
membrane of cell
surface (x 100000).
At this magnification it appears
as two (!) dark
lines at the edge
of the cell.
micrograph of nucleus
outer membrane
inner membrane
matrix
cristae (sing. crista)
lipid
micrograph of mitochondrion (x 40000)
D. Ehrig, Brinkum
organelles_em
Transparency:
Features of cells visible using an electron microscope (3)
cell surface membrane
secretory vesicles
Golgi apparatus
vesicle adding to and
budding from pile of
membranes
Electron micrograph
of Golgi body
(apparatus)
microtubes, some of
which are transporting
secretory vesicles to the
cell surface
Golgi apparatus (x 72500)
Electron micrograph of free ribosomes
Electron micrograph of
endoplasmic reticulum
(x 55000)
Electron micrograph of
“rough” endoplasmic
reticulum
(ER + bound ribosomes)
D. Ehrig, Brinkum
organelles_em
Transparency:
Features of cells visible using an electron microscope (4)
mitochondrion
cytoplasm
nucleus
cell wall
large vacuole
cell surface
membrane
chloroplast
tonoplast
Appearance of a
representative plant
cell as seen with an
electron microscope
(x 12000)
Cell fractionation and ultracentrifugation
In order to study the structure and function of the various organelles which make up cells, it is
necessary to obtain [erhalten, bekommen] large numbers of isolated organelles. There are two stages in achieving [erreichen] this:
• Cell fractionation involves [beinhalten, bedeuten] cells being placed in a cold, isotonic, buffered
solution, for the following reasons:
- cold - to reduce enzyme activity which might break down the organelles
- isotonic [isotonisch = gleiche Konzentration innerhalb und außerhalb der Organelle] - to prevent
organelles bursting due to the influx [Einfließen] of water
- buffered [gepuffert] - to maintain a constant pH [Säuregrad].
They are then broken up using a pestle [Stösel, Pistill] and mortar [Mörser] or an electrical blender
[Mixer/Zerkleinerer] to break the cell membrane and/or wall and release [freisetzen] the organelles.
The resultant fluid is then filtered to remove any complete cells and large pieces of debris
[Reststücke, „Müll“].
• Ultracentrifugation is the process by which fragments in the filtered
liquid are separated in a machine called a centrifuge. This spins tubes
of the liquid at very high speed, to create a centrifugal force. At slower
speeds, only the very heaviest organelles are forced out of suspension,
into a thin deposit [Ablagerung] at he bottom of the tube. This deposit
includes the nuclei, which can be isolated by removing the supernatant
liquid [Überstand(-flüssigkeit)]. This supernatant liquid can then be spun in
the centrifuge at a faster speed, separating out the next most heavy
component [Bestandteil]. By continuing in this way, smaller and smaller
fragments can be separated out.
D. Ehrig, Brinkum
organelles_em