Signal Hypothesis

Signal Hypothesis

Signal Hypothesis - After synthesis the proteins may be incorporated in membranes or may be secreted from the cell. Secretory proteins are synthesized by the ribosomes attached to the endoplasmic reticulum membranes and released into the ER. From here they are transported to various membrane bound compartments, e.g. the Golgi complex and the lysosomes.

They are then secreted from the cell by exocytosis. Blobel and Dobberstein (1975) have proposed the signal hypothesis for selective translation of mRNAs. This hypothesis has been reviewed by Blobel (1978). It is postulated that mRNAs translating secretory Proteins contain a group of signal codons on the 3' side of the initiation codon AUG.

The ER membrane is postulated to have ribosome receptor proteins capable of moving in the plane of the membrane. Free ribosomes translate a polypeptide chain which contains a signal peptide region. On emerging from the ribosome the signal peptide interacts with the ribosome receptor proteins forming a tunnel in the membrane which coincides with the ribosomal tunnel.

An enzyme, signal peptidase cleaves the signal peptide from the growing polypeptide chain. When the chain is completed it is released into the space of the ER. The ribosome detaches from the ER membrane and the ribosome receptor proteins diffuse in the plane of the membrane closing the tunnel.

	Back to Home
Protein Synthesis Part 1 Release of Deacylated tRNA Hydrolysis of GTP Locking and Unlocking Ribosome Model inchworn Theory Conformational Changes Recognition of the Termination Signal Release of the Polypeptide Chain Prokaryote and Eukaryote Release Factors Processing Polypeptide Chain Rate of Protein Synthesis Signal Hypothesis Prokaryote and Eukaryote Protein Synthesis Teminism

Home | Site map | Submit Article | Resources | Search