Protein Synthesis in Eukaryotes- Definition, Enzymes and Process


Ribosomes are the molecular machines responsible for protein synthesis, or translation, in the cell. They are made of ribosomal RNA (rRNA) and proteins, and consist of two subunits: a large subunit and a small subunit. The large subunit sits on top of the small subunit, with a messenger RNA (mRNA) template sandwiched between them.

Protein synthesis is the process by which the genetic information encoded in mRNA is translated into a specific sequence of amino acids, which are the building blocks of proteins. Proteins perform various functions in the cell, such as catalyzing biochemical reactions, forming structures, transporting molecules, and regulating gene expression.

The ribosomes receive their orders for protein synthesis from the nucleus, where portions of DNA (genes) are transcribed to make mRNA. The mRNA travels from the nucleus to the cytoplasm, where it binds to a ribosome near its 5` end. The ribosome then reads the mRNA sequence from the 5` to 3` direction, using transfer RNA (tRNA) molecules to bring the corresponding amino acids to the growing polypeptide chain.

The ribosome has three binding sites for tRNA: the aminoacyl-tRNA site (A site), where the incoming tRNA with its attached amino acid binds; the peptidyl-tRNA site (P site), where the tRNA linked to the growing polypeptide chain is bound; and the exit site (E site), where the tRNA leaves the ribosome after its role in translation. The ribosome catalyzes the formation of a peptide bond between the amino acids at the A and P sites, and then shifts the mRNA by one codon, moving the tRNAs from one site to another. This cycle repeats until the ribosome reaches a stop codon on the mRNA, signaling the end of translation.

Ribosomes can be found either freely floating in the cytosol or attached to the endoplasmic reticulum (ER), a membranous organelle that synthesizes lipids and modifies proteins. The location of ribosomes determines where the proteins they produce end up: proteins synthesized by free ribosomes usually stay in the cytosol or are transported to other organelles, while proteins synthesized by ER-bound ribosomes are usually destined for secretion or insertion into membranes.

Ribosomes are essential for life, as they enable cells to produce proteins that carry out various functions. In eukaryotes, ribosomes are larger and more complex than in prokaryotes, reflecting their different evolutionary origins and cellular needs. In this article, we will explore how protein synthesis occurs in eukaryotes, and how it differs from protein synthesis in prokaryotes.