The Catalyst: RNA and the Quest to Unlock Life's Deepest Secrets

part of their immune surveillance, cells have a natural mechanism for chopping proteins into little pieces and presenting them on their outer surface, where they can be surveyed by T cells.

The purpose of studying the ribosome was to understand protein synthesis, and, as we’ve already learned, the ribosome doesn’t make protein all by itself. It needs mRNA to specify which protein gets made, and it needs tRNAs to bring in the matching amino acids.

day followed night

How could a protein enzyme possibly know how to make a specific DNA sequence as long as six nucleotides? No such enzyme had ever been found. DNA and RNA polymerases are capable of synthesizing long strings of nucleotides, but they don’t do it by themselves—they use DNA as a template. Reverse transcriptases, such as those found in retroviruses, use

they wanted it to use the sequence of A, G, C, and U nucleotides to predict the correct 3D structure.

Hemoglobin, the protein in our red blood cells that carries oxygen, is assembled from four chains of amino acids: two identical alpha-globin chains plus two identical beta-globin chains.

the sequence at one end of the U1 snRNA fit together with the sequences at the start of the known human intron sequences,

The small subunit

ribosome is not a single entity but a pair of enormous complexes each composed of RNA and proteins—called the large and small subunits—