Why can't RNA form a double-stranded structure to replace DNA as genetic material?
answer:
In fact, this question is more complicated, and the level is limited and can only be answered briefly. The first thing to say is that RNA can form a double-stranded structure, such as a single-stranded structure that can form a stable pair of transporter RNAs. But RNA cannot form the long and stable double strands of DNA, so it cannot replace the genetic material that DNA forms in cell organisms.
The chemical properties of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are very similar, the difference is only that DNA has an additional "deoxygenation", as shown in the figure below, the difference between the two is the circled 2' bit.
Although it may seem to be a small difference, if the RNA forms a double strand, the extra oxygen atoms in the 2' position will squeeze each other inside the double strand, resulting in unstable spatial structure and easy destrengulation. In addition, the extra-OH of RNA has high reactivity and is prone to chain breakage, so it cannot form a long and stable double helix structure like DNA.
For cell organisms, their genetic material must contain all the information needed to form one or more cells, and must have a certain degree of stability to ensure that the next generation of cells can carry out various physiological activities normally. RNA cannot form long and stable double-stranded structures, and single-stranded structures are not stable enough, so it is not a good choice for genetic material. However, many viruses use RNA as genetic material because viruses do not have a cellular structure and rely on host cells for life activities. The mutation-prone nature of RNA gives the virus more opportunities to mutate, so that more suitable variants can be screened to infect more cells.
Resources:
[1] Why does DNA form a double helix structure (and become the primary genetic material) while RNA cannot?
[2] Rana, T. Illuminating the silence: understanding the structure and function of small RNAs. Nat Rev Mol Cell Biol8, 23–36 (2007).
by fiufiu