Lectures: 2,011 | Views: 49,626,878 | Subscribers: 380,859 | Subscribe
Signal Sequences and Signal-Recognition Particles
In eukaryotic cells, ribosomes begin polypeptide synthesis in the cytosol of the cell. These ribosomes are called free ribosomes because they are not actually attached to any organelle in the cell and are found floating within the cytoplasm itself. If the polypeptide chain being synthesized is destined to remain in the cells cytoplasm, then the ribosome will remain a free ribosome and will carry out the process of translation within the cytosol. However, if the polypeptide is destined to be either secreted by the cell or integrated with the plasma membrane, the ribosome will move onto the membrane of the endoplasmic reticulum, where it will finish the synthesis process. Polypeptides that are destined for secretion or to be embedded in the plasma membrane contain a sequence of amino acids towards the beginning of the growing polypeptide chain. This sequence is known as the signal sequence because it signals a special group of molecules known as the signal-recognition particles (SRP) to bind to it and bring the entire ribosome complex onto the membrane of the ER. The SRP-ribosome complex binds to a special region on the ER membrane known as the SRP receptor. Once it binds, a protein channel known as the translocon opens up and allows the growing polypeptide chain to extend into the ER lumen.
[{"id":"sLdJTcBnO3c","title":"Introduction to DNA","link":"http:\/\/www.aklectures.com\/lecture\/introduction-to-dna"},{"id":"9unpqe8087E","title":"DNA Replication: Helicase and Unwinding","link":"http:\/\/www.aklectures.com\/lecture\/dna-replication-helicase-and-unwinding"},{"id":"gxeak5TuRIk","title":"DNA Replication: Leading and Lagging Strand","link":"http:\/\/www.aklectures.com\/lecture\/dna-replication-leading-and-lagging-strand"},{"id":"WONqRyoi49A","title":"Summary of DNA Replication","link":"http:\/\/www.aklectures.com\/lecture\/summary-of-dna-replication"},{"id":"dcvtHSFzKOQ","title":"mRNA, rRNA and tRNA","link":"http:\/\/www.aklectures.com\/lecture\/mrna-rrna-and-trna"},{"id":"IsMHhnGILwg","title":"RNA Transcription","link":"http:\/\/www.aklectures.com\/lecture\/rna-transcription"},{"id":"ertPYuifrQM","title":"Post-Transcriptional Modifications of mRNA","link":"http:\/\/www.aklectures.com\/lecture\/post-transcriptional-modifications-of-mrna"},{"id":"9OvzIpQhXTw","title":"The Genetic Code","link":"http:\/\/www.aklectures.com\/lecture\/the-genetic-code"},{"id":"1fUswlOwslw","title":"Translation: Ribosomes and Initiation","link":"http:\/\/www.aklectures.com\/lecture\/translation-ribosomes-and-initiation"},{"id":"5nMEpRG-az8","title":"Translation: Elongation and Termination","link":"http:\/\/www.aklectures.com\/lecture\/translation-elongation-and-termination"},{"id":"kp06l4zx7Pw","title":"Signal Sequences and Signal-Recognition Particles","link":"http:\/\/www.aklectures.com\/lecture\/signal-sequences-and-signal-recognition-particles"},{"id":"PMsxwRCliBE","title":"Post Translational Modifications","link":"http:\/\/www.aklectures.com\/lecture\/post-translational-modifications"}]
Comments
Playlists
Login to create and share playlists