Question

Ribosomes are attached to the endoplasmic reticulum through glycoproteins known as Ribophorin I and II. Which subunit of ribosomes get attached to the endoplasmic reticulum?
A. Large subunit
B. Small subunit
C. tRNA
D. mRNA

Answer 1

Hint:-Ribosomes are small particles which consist of RNA and associated proteins present in large numbers in the cytoplasm of living cells which perform biological protein synthesis.

Complete Answer:-
Ribosomes are composed of two major components i.e. the small and large ribosomal subunits also known as ribozymes. Each ribosomal subunit consists of one or more ribosomal RNA molecules (rRNA) and ribosomal proteins.
(a) Small subunit- Each ribosome consists of a small component (30S). It mainly decodes the genetic message and it also binds with the mRNA.
(b) Large subunit- Ribosome consists of a larger subunit (50S). It primarily has a catalytic function and it binds with the aminoacylated tRNAs.
These ribosomes constantly attach and detach from the endoplasmic reticulum as they are not a part of a stable organelle. They attach when the ribosome begins to synthesize proteins that are going to be secreted. Ribophorin which is a transmembrane glycoprotein or ribosome receptor protein plays a vital role in the binding of ribosomes to the outer surface of the endoplasmic reticulum forming rough endoplasmic reticulum. They fix the larger subunit (50S) of the ribosome to the rough endoplasmic reticulum.
Whereas tRNA or transfer RNA which is a small RNA molecule and participates in protein synthesis carries amino acids to the site of protein synthesis in ribosomes during the process of translation. While mRNA or messenger RNA serves as an intermediary between protein and DNA and carries the coding sequence for the protein synthesis.

So, as we have discussed above the correct option is A (Large subunit).

Note:- Rough endoplasmic reticulum main function is to support the structure and storage of proteins. Ribosomes constantly link and separate from the surface of E.R. and this connection between ribosomes and endoplasmic reticulum is through signal recognition particles.