Permease
Permeases are proteins , the passive molecules or ions through the cell membrane transport . You are independent of ATP . In evolutionary terms, permeases are a heterogeneous group, which means that evolution has re-invented them many times and can therefore only be comprehensively recorded on the basis of a long list. Permeases are among the transport proteins .
Cells are constantly exchanging substances with their environment. The cell membrane is normally not permeable to most substances (especially polar substances such as ions or larger molecules such as glucose (= selectively permeable )). So -called permeases are formed so that these can still be transported through the cell membrane .
These proteins are embedded in the cell membrane and connect the inside of the cell with the outside world so that substances can be exchanged. Because the protein passes through the membrane, such molecules are called transmembrane proteins or "integral proteins". The term permease is only used in connection with enzymes such as lactose permease, where it is a synonym for transporter .
This type of transport is known as secondary active transport . This means that the energy used does not come from the hydrolysis of ATP . A concentration gradient of another, simultaneously transported substance serves as the energy source. Most often, a sodium ion or proton gradient is used for this. Some permeases also transport substances passively if they have a corresponding concentration gradient in the direction of transport. This type of transport is also a co-transport, since two different substances are transported at the same time. See proton pump .
In prokaryotes , the biosynthesis of permeases is often controlled by so-called operons . This means that the cell only produces the permeases when they are needed. Such an operon then initiates the production of the permease.
A well-known permease is LacY and occurs in the cell membrane of bacteria . It enables the transport of lactose into the cell interior (see lac operon ).
See also
Individual evidence
- ↑ G. Poeggel: Short textbook biology. 2005, ISBN 3-13-140981-9 , p. 20.