Question

what are the steps of how membrane bound proteins get into the membrane starting with new mRNA?

Answer 1

The messenger RNA formed after transcription is premature. It is converted into mature messenger RNA by RNA processing. This process includes capping, tailing and splicing of RNA.

In capping, 7 methyl guanosine cap is added to the 5' end of mRNA with the help of capping enzyme.

In tailing, poly adenine residues are added to the 3' end of mRNA by polyA polymerase enzyme.

In splicing, all the exons are joined together and all the introns are removed.

Once mature messenger RNA is formed, RNA is transported out of the cytoplasm.

Now the mature messenger RNA undergoes translation in cytoplasm. It associates with transfer RNA and ribosomal RNA and ribosomes to form translation elongation complex. This leads to the formation of peptide chain which contain multiple residues of amino acids

This is a protein in its primary structure. It is simply a sequence of amino acids. The proteins are folded for other and are chemically modified by undergoing post translational modification. It occurs in endoplasmic reticulum and golgi apparatus.

Once post translational modification is completed a protein achieves its final structure which is called as three dimensional or native structure of protein.

Now the protein is ready to be inserted into the The membrane of a specific organelle or into cytoplasm of cell or is secreted outside the cell.

If the protein is destined to be transported into the membrane of an organelle, then it contains a specific sequence called as signal sequence. This is recognised by signal recognition particle. This particle take the protein to the targeted organelle. For example the signal sequence for targeting into endoplasmic reticulum membrane is KDEL or KKXX.

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