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MOVEMENT OF PLASTIC BEADS BY KINESIN, A MOLECULAR MOTOR PROTEIN. Many cargoes (organelles, RNAs and proteins) are transported within cells along microtubule tracks by molecular motor proteins. This motion can be reconstituted with purified proteins in a “test tube”. Here a molecular motor protein called kinesin is attached to a plastic bead that is 1 micron in size (one-millionth of a meter) and these motors transport the plastic beads along a microtubule track (made from purified tubulin). This video is shown in “real time” and the motion occurs at a rate of 0.5 microns per second. Credit: Ron Vale (UCSF)
MICROTUBULES GROWING FROM A CENTROSOME (IN A TEST TUBE!). Microtubules are long polymers of a protein called tubulin. During mitosis, the cell's nuclear membrane breaks down, and the "mitotic spindle" (made of hundreds of microtubules) is formed which organizes the chromosomes to prepare for cell division. In many cells, microtubules grow out of “centrosomes”, which are special microtubule nucleating and organizing structures in cells. Microtubules also serve as tracks for cargo transport in "interphase" (when the cell is not dividing). Here, purified centrosomes were added to the purified cytoplasm of a frog egg, along with some fluorescently-labeled tubulin protein. You can see microtubules growing out of the centrosome and also exhibiting a property called “dynamic instability” where they grow and shrink. You can also see a background flow of the solution. This is a time-lapse move (sped up in time). Credit: Tim Mitchison (Harvard Medical School) and Tony Hyman (Max Planck, Dresden)
MOLECULAR MOTOR PROTEINS WALKING ALONG MICROTUBULES. The linear tracks labeled with a blue fluorescent dye are microtubules, long polymers (large molecules made up of repeated subunits) that serve as roadways for transport inside of cells. The yellow dots (from a fluorescent dye) are individual dynein molecules, proteins that hydrolyze (breakdown) ATP and that move along microtubules. These proteins are only ~25 nm wide (about one-millionth of an inch) and labeled with a single fluorescent dye molecule. Yet we can see the fluorescent tag with modern microscopes and very sensitive scientific ccd cameras (which cost about $25,000). The motion that you see here is happening outside of a cell and in a “test tube” environment (actually a small chamber made using a microscope slide and coverslip). Molecular motors transport various cargoes (such as membrane organelles or proteins) to different destinations inside of the cell. This is a time-lapse move (sped up in time). Credit: Samara Reck-Peterson, Harvard Medical School


RNA POLYMERASE TRANSCRIBING RNA FROM DNA. (Slide view before movie starts) RNA polymerase is a molecular machine that reads the genetic code on a DNA molecule and transcribes it onto a messenger RNA. In doing so, RNA polymerase rotates DNA, as seen in the movie on the right. The right-handed double helix of DNA passes through the RNA polymerase as if a right-handed screw goes through its mate nut. (To observe rotation, a magnetic bead was attached to the tail end of DNA and the bead was pulled upward by a magnet. A small fluorescent bead served as a maker of rotation.) Credit: Kazuhiko Kinosita (Waseda University, Japan)
ROTARY MOTION OF THE MOTOR THAT PRODUCES ATP IN MITOCHONDRIA. (Slide view before movie starts) Mitochondria are organelles within the cell that are sometimes called "the power plant of the cell" because they produce chemical energy in the form of a molecule called ATP. ATPases are enzymes that breakdown (hydrolyze) ATP to release energy. The F1 ATPase is a rotary motor that sits in the membrane of mitochondria. It consists of a protein “donut” with a shaft that rotates in the middle. To see the shaft rotate, scientists attached a long rod (an actin filament that is a few microns) to the shaft; this long rod was tagged with fluorescent dyes and hence the rod can be visualized with a fluorescent microscope. In this experiment, the protein was separated from the mitochondrial membrane and placed on a glass coverslip. When given ATP, the motor hydrolyzes the ATP, rotates its shaft and spins the actin filament around. Normally, when in a mitochondrial membrane, the motor operates in reverse. There is pH gradient that causes the shaft to rotate in the opposite direction and this motion of the shaft causes ATP to be synthesized from ADP and phosphate. Amazingly, this process operates with >98% efficiency! Much better than your car. Movie is shown in “real time”.Credit: Kazuhiko Kinosita (Waseda University, Japan)
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