Question

Expand the terms : RNA and DNA

Answer 1

The structure of DNA and RNA. DNA is a double helix, while RNA is a single helix. Both have sets of nucleotides that contain genetic information. Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce.

Answer 2

RNA and DNA are simple linear polymers consisting of only four major types of subunits, and yet these molecules carry out a remarkable diversity of functions in cells and in the laboratory. Each newly-discovered function of natural or engineered nucleic acids enforces the view that prior assessments of nucleic acid function were far too narrow and that many more exciting findings are yet to come. This Perspective highlights just a few of the numerous discoveries over the past 20 years pertaining to nucleic acid function, focusing on those that have been of particular interest to chemical biologists. History suggests that there will continue to be many opportunities to engage chemical biologists in the discovery, creation, and manipulation of nucleic acid function in the years to come.

DNA makes RNA makes protein. This is the shorthand version of Francis Crick's “central dogma” of biology, which more specifically states: “the transfer of information from nucleic acid to nucleic acid, or from nucleic acid to protein may be possible, but transfer from protein to protein, or from protein to nucleic acid is impossible” (Crick 1958). Crick was referring to information that defines the precise sequence of residues within a nucleic acid or protein. He confessed at the outset of that 1958 paper: “(James) Watson said to me, a few years ago, ‘The most significant thing about nucleic acids is that we don't know what they do’”. Yet in that same paper Crick proposed that RNA does much more than serve as a passive carrier of information. He hypothesized that it functions as an “adaptor” molecule, carrying amino acids to the RNA template that directs the sequential assembly of amino acids to form proteins. He suggested that there would be (at least) one adaptor for each of the 20 amino acids, although he felt the task of joining the adaptor to its amino acid would be too challenging for RNA.

Crick's adaptor is of course tRNA, which he later said “looks like Nature's attempt to make RNA do the job of protein” (Crick 1966). Crick went further to say: “It is tempting to wonder if the primitive ribosome could have been made entirely of RNA”, and he suggested: “Possibly the first ‘enzyme’ was an RNA molecule with replicase properties” (Crick 1968). Similar comments regarding the catalytic potential of RNA also were made at that time by Woese (1967) and Orgel (1968). When Chemistry & Biology published its introductory issue in 1994, the modern ribosome was looking very much like an RNA enzyme (Noller et al., 1992), although that was still to be proven definitively based on examination of its X-ray crystal structure (Nissen et al., 2000). RNA enzymes had been discovered in nature (Kruger et al., 1982; Guerrier-Takada et al., 1983) and invented in the laboratory through test-tube evolution (Bartel and Szostak, 1993), but even a rudimentary form of a replicase was many years away (Lincoln and Joyce, 2009).

Certainly one of the most dramatic developments in chemical biology over the past 20 years has been the growing appreciation of the many complex functional roles that RNA plays in biology and can be made to play in chemical systems. Even DNA can get into the act of ligand binding and enzymatic function. The central dogma still holds, but nucleic acids are much more than carriers of information. They are both egg and chicken, and we still don't know all that they can do.