Intracellular transport of auxins / copper / proteins / nucleosides / virions
Transport between organelles
between organelle and membrane
In intracellular transport , molecules , membrane components and proteins anchored in them are transported through the interior of a cell (in contrast to membrane transport and paracellular transport , in which substances are moved through biomembranes or between cells). Water-soluble substances are enclosed in vesicles , while membranes and proteins anchored in them become part of the vesicle envelope. Active and directed transport is achieved by moving the vesicles along with motor proteins that bind to the microtubules of the cytoskeleton . Their target can either be other vesicles and organelles , but also the outer cell membrane . A particularly impressive example of intracellular transport is axonal transport in neurons .
Vesicular intracellular transport
Transport between organelles
Vesicular intracellular transport takes place between different cell organelles. Particularly noteworthy here are the endoplasmic reticulum (ER) and the Golgi apparatus , but also endosomes , lysosomes and certain membrane components such as B. the presynaptic membrane . An example would be the transport of proteins that are intended for secretion: These are first packed in vesicles which move in the direction of the Golgi apparatus. Here, however, it happens that this also happens with proteins that should not leave the ER. These can be recognized by receptors using a specific amino acid sequence (KDEL signal sequence ) and transported back again.
Absorption of substances
If molecules are to be taken up from outside the cell, the process of endocytosis takes place. The resulting transport vesicles now fuse to form endosomes and, following the course of the microtubules, get further inside the cell, where they either fuse with lysosomes, which results in the breakdown or release of the substances they contain, or split some vesicles and reach the cell membrane again, with which they can fuse again.
Release of substances
Intracellular transport can also serve to release substances: here it is often proteins that are packaged in the ER and then pass through the Golgi apparatus to the cell membrane, where they are released into the environment in the process of exocytosis . The proteins synthesized in the ER itself are connected to the membrane, which is why they are not released in the process, but rather are stored in the cell membrane. Also neurotransmitter intracellularly stored in vesicles and transported, and then by exocytosis into the synaptic cleft to arrive.
Non-vesicular intracellular transport
In contrast to the vesicular transport used for water-soluble molecules or proteins, there is another mechanism for hydrophobic substances: These are not stored in vesicles, but bind to proteins that have binding pockets for them, but are themselves hydrophilic on the outside and thus the Facilitate movement through the cytoplasm , much like albumin does in the blood.
- ↑ J. Rassow, K. Hauser, R. Netzker, R. Deutzmann: Biochemie , Thieme (2006), ISBN 978-3131253514 , p. 388
- ↑ a b c B. Alberts, A. Johnson, J. Lewis, M. Raff, K. Roberts, P. Walter: Molecular Biology of the Cell , 5th Edition, Garland Science (2008), ISBN 978-0-8153 -4106-2 , pp. 749-809.
- ^ FR Maxfield, M. Mondal: Sterol and lipid trafficking in mammalian cells (PDF, 338 kB). In: Biochemical Society Transactions (2006), Volume 34, part 3