Directing Traffic: How Vesicles Transport Cargo
Most molecules, including proteins, are too large to pass directly through membranes. Instead,
large molecules are loaded into small membrane-wrapped containers called vesicles. Vesicles are
constantly forming - especially at the plasma membrane, the ER, and the Golgi. Once formed,
vesicles deliver their contents to destinations within or outside of the cell.
A vesicle forms when the membrane bulges out and pinches off. It travels to its destination then
merges with another membrane to release its cargo. In this way proteins and other large
molecules are transported without ever having to cross a membrane.
Some vesicles form with the help of coat proteins. Geometrically arranged coat proteins on the surface of the membrane help the vesicle to bud off.
Exploding Transport Containers
Fluorescent dots (transport containers) explode in a burst of light as they fuse with the plasma
membrane and expel their contents out of the cell.
Video courtesy Kai Simons, Professor and Executive Director, Max-Planck
Institute for Molecular Cell Biology and Genetics, Dresden, Germany. Reproduced from the Journal of Cell
Biology (2000), 149: 33-40. ©2000 The Rockefeller University Press.
Vesicles Travel Cellular Highways
Busy cells are often filled with thousands of traveling vesicles. To help
organize these vesicles and get them pointed in the right direciton, the cell uses
the rigid filaments and tubes of the cytoskeleton. Special motor proteins attach
to cargo-filled vesicles and carry them along the cytoskeleton like trucks on a highway.
Different motor proteins are specialized for carrying certain types of cargo and for traveling
along the cytoskeleton in one direction or the other. Careful matching of motors with their
cargo helps vesicles reach their targets.
Motor proteins attach to vesicles and walk along a microtubule of the cytoskeleton. Dyneins
walk toward the microtubule organizing center (MTOC, or centrosome) and kinesins walk away from the MTOC.
Real-time video of vesicles traveling along neurons inside a living fruitfly embryo. The three
columns of moving vesicles show the locations of three different nerves. Each nerve is a bundle
of axons from many neurons (a specialized cell type of the nervous system). The vesicles are
visible because they contain Green Fluorescent Protein.
Video courtesy Bill Saxton, Ph.D., Professor of Molecular Cell & Developmental Biology, University of California Santa Cruz.
A Different Kind of Motor
Some vesicles have unusual ways of getting around the cell. The ones shown here can be
seen rocketing through the cytoplasm. To do this they build up actin proteins (in red)
at their rear. The polymerization of actin into short filamets acts as a molecular jet pack.
Video courtesy Jack Taunton, Ph.D., Associate Professor, Cellular and Molecular Pharmacology, University of California San Francisco.Reproduced from the Journal of Cell Biology (2000), 149: 519-530.
2000 The Rockefeller University Press.
Genetic Science Learning Center. (2010, September 2) Directing Traffic: How Vesicles Transport Cargo.
Retrieved January 14, 2017, from http://learn.genetics.utah.edu/content/cells/vesicles/
Directing Traffic: How Vesicles Transport Cargo [Internet]. Salt Lake City (UT): Genetic Science Learning Center; 2010
[cited 2017 Jan 14] Available from http://learn.genetics.utah.edu/content/cells/vesicles/
Genetic Science Learning Center. "Directing Traffic: How Vesicles Transport Cargo." Learn.Genetics.September 2, 2010. Accessed January 14, 2017. http://learn.genetics.utah.edu/content/cells/vesicles/.