From this lecture, I learnt the detailed history of RNA. I learnt that RNA and DNA are highly important components that contributed greatly to the emergence of life. The DNA sequence continues to evolve, and its change is influenced by external factors such as environment, mutations and infections.
Avery, McCarty and MacLeod identified that the transforming principle is DNA, not protein – by using heat-killed S cells and seeing if S cells reappear if different enzymes were added. Hershey-Chase ‘s experiment used bacteriophages whose DNA and protein coat was each labeled by radioactive 32P and 35S to infect the bacteria. Resulting that only 32P was found inside the bacteria. This has proved that DNA, not protein, is the genetic material. DNA’s composition was found by Erwin Chargaff, Maurice Wilkins, Francis Crick, James Watson and Rosaline Franklin.
RNA performs like an enzyme catalyst as it links different reactions. RNA folds into a complex structure when produced. Their unique structure is identified by the different cleavage sites. RNA can also perform bond formation by a ribosome, sensing by riboswitch, and storage of genetic information by RNA virus. The hypothesis is that once in history, only RNA existed and RNA mutated into DNA and proteins because proteins have greater diversity, thus can perform better. DNA just stores genetic information and protein produces DNA; however, RNA has both former and latter functions. Thus, the survival of the fittest is applied to RNA which can produce a stable protein.
Origin of life was explained by the primordial soup theory. There are many types of RNA, but only mRNA is a coding RNA. There are numerous non-coding RNAs. MicroRNA (miRNA) is useful as it regulates the targets across multiple signal transduction pathways, so is a useful therapeutic component; it interacts with different mRNAs to have more than one function. For example, miRNA inhibits translation and leads to less protein production. Long non-coding RNAs are used as diagnostic markers, risk genes, prognostic markers, and therapeutic targets.
Epigenetics means that the phenotype is changed not because the DNA sequence is changed, but because of the change in gene expression by DNA methylation, histone modification and non-coding RNAs. They can activate and deactivate genes. Only the activated DNA are expressed when they are read and transcribed into RNA, then translated into proteins by ribosomes.
Genetics and epigenetics are both important. RNA epigenetics allows the development of therapeutics. For example, there is a case where a 3-year-old kid was helped by the new drug, nusinersen which had the role of restoring functional proteins. RNA is also useful in making mRNA vaccines, diagnosis and treatment of cancer. Also, the genome project has promoted next-generation sequencing.