Question

If the hypothesis that protocells were based on an "RNA world" is correct, which would NOT be necessary to shift to a "DNA world"?

Answer 1

If the RNA world hypothesis is correct, shifting to a DNA world would not necessitate prebiotic synthesis of complex nucleotides or proteins. Instead, it proposes RNA's dual genetics and catalytic roles were precursors to the evolution of DNA as a stable genetic molecule and proteins for catalysis, implying gradual evolutionary transitions facilitated by enzymes like reverse transcriptase.

Step-by-step explanation:

If the hypothesis that protocells were based on an RNA world is correct, shifting to a "DNA world" would not require the prebiotic synthesis of complex nucleotides or the earlier existence of proteins for catalysis or structural purposes. In an RNA world, RNA molecules have the dual functionality of storing genetic information and catalyzing chemical reactions, addressing the "chicken-and-egg" problem of whether proteins or nucleic acids came first. However, the RNA world hypothesis suggests that the transition to DNA and proteins from RNA was a subsequent evolutionary step, with DNA taking over the role of genetic information storage due to its more stable double-stranded structure and proteins assuming the role of catalysts and structural elements in the cell due to their diverse functions.

During the hypothetical transition from the RNA world to a DNA-based world, enzymes such as reverse transcriptase, which can transcribe RNA back into DNA, could have played a critical role. These enzymes could be seen as a bridge in the evolutionary process, suggesting that an intermediate stage involving RNA and proteins (RNP World) may have preceded the current DNA and protein-based cellular life (DNP World). The development of a stable mechanism for information storage and retrieval with DNA and the diversification of catalytic functions with proteins would have relegated RNA to a more intermediary role, mediating between genes and proteins.

Answer 2

In the hypothesis of an RNA-based protocell world, the shift to a DNA world would not require a new translation system since RNA already possessed the ability to encode and transfer genetic information. Reverse transcriptase would facilitate the transition to the stable DNA structure, enabling a more efficient and reliable genetic code without the need for new mechanisms.

Step-by-step explanation:

The Shift from an RNA World to a DNA World

When considering the hypothesis that protocells were based on an "RNA world", the shift to a "DNA world" would not require the de novo appearance of nucleic acid information storage and protein-based catalytic metabolism. This is because RNA is capable of carrying out necessary chemical reactions and can encode genetic instructions, traits that are essential in today's DNA and proteins.

If the transition from an RNA world to a DNA world happened, it likely included the addition of DNA as a more stable information molecule and the development of proteins to assist in structure formation and catalysis. In this scenario, a component that would not be necessary for the shift would be a reverse transliteration system or a complicated 'translation' process, as RNA already has the capability to store and transfer information necessary to synthesize proteins.

Considering the RNA world hypothesis, it's suggested that RNA was capable of self-replication and catalysis, offering a solution to the chicken-and-egg problem of whether proteins or genetic materials came first. However, the transition to a DNA-based system required a molecule to retro-transcribe RNA back into DNA. This process likely involved an enzyme similar to retroviral reverse transcriptase, facilitating the movement to a more stable DNA-based genetic storage without the need for an entirely new system of genetic transfer and protein synthesis.

Ultimately, in an RNA world, the direct transition to a stable, DNA-based genomic structure would not necessitate a set of entirely new biochemical mechanisms, as the RNA world hypothesis proposes that RNA already fulfilled most roles required for life to evolve. Therefore, the use of DNA serves to enhance the efficiency and stability of the genetic information storage, rather than to rebuild the functions from scratch.