Question

-what are the roles of ribosome, ER signal sequence, Signal Recognition Particle, SRP receptor, translocation complex in translation and movement of proteins into the endoplasmic reticulum?

Answer 1

Roles of Ribosome:

Ribosomes are composed of ribosomal RNA and proteins. Ribosomal subunits transfer to the cell body and attach to the rough ER. Ribosomes read strands of messenger RNA and bind matching units of transfer RNA to the currently read portion. The ribosome and its associated enzymes transfer an amino acid from the transfer RNA to an elongating length of protein in a process called translation.

Roles of Translocation Complex:

The Translocation Complex or Translocons are tiny docking stations on the rough ER surface that lock onto ribosomes. When a ribosome begins making proteins, the translocon opens enough for the newly created protein to feed into the pore. The new protein passes through the pore in a linear or helical form, because the pore is too small to allow a folded protein to pass within. The translocon pore only opens if it recognizes a special sequence of amino acids that ribosomes use to start a newly created protein.

Roles of ER Signal Sequence:

The general role of signal sequences in targeting proteins to their appropriate locations within the cell was first elucidated by studies of the import of secretory proteins into the ER. The ER Signal Sequence is a short peptide (usually 16-30 amino acids long) present at the N-terminus of the majority of newly synthesized proteins that are destined towards the secretory pathway. When this sequence sticks out of the ribosome, it’s recognized a protein complex called signal-recognition particle (SRP), which takes the ribosome to the ER. There, the ribosome feeds its amino acid chain into the ER lumen (interior) as it's made.

Roles of Signal Recognition Particle:

The signal recognition particle (SRP) is an abundant, cytosolic, universally conserved ribonucleoprotein (Protein-RNA complex) that recognizes and targets specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes. In eukaryotes, SRP binds to the signal sequence of a newly synthesized peptide as it emerges from the ribosome. This binding leads to the slowing of protein synthesis known as "elongation arrest," a conserved function of SRP that facilitates the coupling of the protein translation and the protein translocation processes. SRP then targets this entire complex (the ribosome-nascent chain complex) to the protein-conducting channel, also known as the translocon, in the ER (Endoplasmic reticulum) membrane. This occurs via the interaction and docking of SRP with its cognate SRP receptor that is located in close proximity to the translocon.

Roles of Signal recognition particle receptor:

Signal recognition particle (SRP) receptor, also called docking protein, is a dimer composed of 2 different subunits that are associated exclusively with the rough ER in mammalian cells. Its main function is to identify the SRP units. SRP (signal recognition particle) is a molecule that helps the ribosome-mRNA-polypeptide complexes to settle down on the membrane of the endoplasmic reticulum.