The Science of Existence (89-4) Ribosomes


Ribosomes translate sequences of nucleic acids into sequences of amino acids. ~ Israeli systems biologist Shlomi Reuveni et al

Although not membrane-bound, ribosomes are considered organelles. Ribosomes are protein factories; producing their products in an intricate, multi-step process. Nearly all the proteins required by cells are synthesized by ribosomes. Ribosomes receive their instructions from the cell nucleus and obtain their construction materials from the cytoplasm.

A ribosome assembles a particular protein by translating information encoded in messenger RNA (mRNA). While many ribosomes churn out a wide variety of proteins, some specialize to manufacture only certain products. A single cell may have thousands of ribosomes.

Ribosomes are composed of 55 to 80 proteins, depending on organism type. Highly ordered, these structural proteins are unusually short and uniform in length. Ribosomes also have 2–3 strands of RNA, which account for up to 70% of the total mass of the ribosome.

The ribosomes of archaea, bacteria, and eukaryotes differ in structure and composition. But the subunits within are similar between prokaryotes and eukaryotes.

The ribosome is universal biology. ~ American biochemist Loren Williams

Prokaryotic ribosomes produce proteins using a slightly different process than eukaryotic ribosomes. But the core translation mechanics of the ribosome are essentially the same in all organisms. To meet production requirements, the outer regions of ribosomes expand and become more sophisticated as organisms become more complex.

Prokaryotic ribosomes are ~20 nm in diameter and contain 65% RNA and 35% ribosomal proteins. Eukaryotic ribosomes are 25–30 nm in diameter, with an RNA-to-protein ratio close to 1. The RNA in ribosomes account for ~85% of a cell’s RNA pool. The number of ribosomes within a cell varies greatly, from less than 10,000 to up to 10 million.

Defective mRNAs result in aberrant, potentially harmful proteins; so special proteins surveil production and ensure quality control.

Ribosomal RNA itself plays a vital role in all stages of protein synthesis.