membrane of cell surface (x 100000). At this magnifi-cation it appears as two (!) dark lines at the edge of the cell.
micrograph of mitochondrion (x 40000)
outer membrane inner membrane lipid
matrix cristae (sing. crista)
micrograph of nucleus
D. Ehrig, Brinkum organelles_em
cell surface membrane
secretory vesicles Golgi apparatus vesicle adding to and budding from pile of membranes
microtubes, some of which are transporting secretory vesicles to the cell surface
Transparency:
Features of cells visible using an electron microscope (3)
Electron micrograph of Golgi body (apparatus)
Golgi apparatus (x 72500)
Electron micrograph of endoplasmic reticulum (x 55000)
Electron micrograph of “rough” endoplasmic
reticulum (ER + bound ribosomes)
Electron micrograph of free ribosomes
D. Ehrig, Brinkum organelles_em
Transparency:
Features of cells visible using an electron microscope (4)
large vacuole
cell wall
cell surface membrane
chloroplast
mitochondrion
Appearance of a representative plant cell as seen with an electron microscope (x 12000)
nucleus
tonoplast
D. Ehrig, Brinkum organelles_em
cytoplasm
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 sta-ges 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.
