Central Dogma - The Definitive Guide | biology dictionary (2023)

Definition

The central dogma was established by Francis Crick in the late 1950s, who held that genetic information flows mainly from nucleic acids in the form of DNA and RNA to functional proteins during the process of gene expression. What makes the core dogma so groundbreaking is its correctness at a time when genomic research was still in its infancy. The central dogma of genetics does not describe the mechanics of protein synthesis, but it does tell us that gene expression follows an almost predictable pattern.

What is the central dogma of biology?

In looking at what the core dogma is, we must first understand the word "dogma" and why that isn't the best use of it. Crick later admitted that a better term would have been "principle".

A dogma is a set of principles that someone in authority holds to be true. This means that the central dogma of gene expression must always be true.Franz Crick, as the leading authority on molecular science in the 1950s and 60s, did not mean that these steps from DNA to RNA to protein could not be reversed. Rather, he suggested that this was the predominant direction in which gene expression flowed.

Crick's idea in more ways than oneit isa dogma – without deoxyribonucleic acids and ribonucleic acids, protein synthesis cannot take place in living cells. In addition, once a piece of the genetic code has entered a protein, that protein is no longer able to alter the original DNA code sequence. In other words, we still haven't been able to prove that a naturally synthesized protein can rewrite DNA - the flow of information from the genome to DNA to RNA to protein within the confines of a cell is a dogma.

The basics of protein synthesis are not discussed in this article. The reader should be familiar with the protein synthesis steps of transcription and translation of nucleic acids, messenger and transfer RNA, ribosomes, amino acids, peptides and proteins.

Crick's Dogma - A Boy Scout

At the time of Crick's ideas, transfer RNA (tRNA) had not yet been discovered. Crick theorized that a small molecule must be present to transport amino acids to the ribosome—at the time, these organelles were called microsomes, and no one was sure of their role. Even current basic knowledge, such as the need for nucleic acids for protein synthesis, was still largely unknown in the 1950s, messenger RNA (mRNA) was only discovered in the 1960s; his research was published the following year. While many articles to this day argue about the central dogma of biology, Crick's theory was groundbreaking at the time. It was he who predicted that in the future we might be able to track evolution using gene sequences - a research area that is currently transforming the way we classify living organisms.

Crick also argued that the most important function of our DNA is to control protein synthesis. In a moment whereScientists knew very little about the role of genes, this was the best description of the relationship between DNA, RNA and protein when no one really knew what genetic information was made of or how it was used.

We must therefore first place this theory in the correct historical framework. It may not be dogma, but its powerful message has propelled genetic research into the future.

Definition of Central Dogma

Another much-discussed point about Crick's dogma is its gist. ManyStudents are simply informedthat this theory is about the rigorous steps of transcription, translation, and protein synthesis.

However, the central dogma of molecular biology holds that the genetic information encoded in DNA is transcribed into mRNA, with each mRNA molecule carrying the information needed to make proteins. He claims that this sequenced flow can be reversed at certain points, but not from protein to nucleic acid. The unidirectional flow from transcription through translation to protein synthesis isnoo Dogma zentral.

The only dogma of Crick's theory (or premise) is, as yet to be seen, that genome sequences are altered by an intracellularly synthesized protein. In their eyes, it has been shown that there is reverse transcription between DNA and RNA; reverse translation between protein and RNA was not detected. Back translation would mean that the amino acids in a polypeptide or protein can recognize tRNA anticodons and assemble them into a new RNA molecule. This can be done synthetically in a laboratory but is not a natural intracellular process.

Crick's dogma does not say that back-translation is impossible, but that it must occur through very different molecular mechanisms. Regarding prions (discussed later) there is reverse translation of the protein into the genome; However, this process requires specific enzymes that are not present in the normal cellular environment to recognize and bind to tRNA anticodons.

After all, the central dogma is not a single propositional statement, but an entire theory. If you look at the central dogma of the definition of biology from a non-scientific source, you will probably read about the flow of protein synthesis from DNA to protein via RNA. The central dogma diagram below is a typical fuzzy representation. This is sometimes referred to as the order of the central dogma. Crick's discovery is much more than a single statement and should never be absolute - he was aware that genetic research still had a long way to go.

Exceptions to the Central Dogma

The reverse transcription is sometimes included as a central dogmatic exception. As we have seen, Crick did not deny the existence of reverse flow between DNA and RNA. It also means that retroviruses provide no evidence of an exception to the rule. Retroviruses transcribe RNA into DNA using the enzyme reverse transcriptase. The only way to add retroviruses as an exception to the "rule" is in the form of extremely primitive retroviruses that lack DNA. Information flow can only take place between RNA and protein.

The other oft-cited exception to Crick's core dogma is the prion - in prions, abnormal proteins "replicate" themselves by changing the shape of surrounding proteins. They infect and change instead of reproducing. Infectious protein particles, only recently discovered, are unique. Although cases of "scrapie," a disease that caused sheep to scrape fences and trees, were recorded as early as 1732, very little historical evidence can point to the evolution of the prion. Like a natural protein that has been misfolded at some point, the prion contains no genetic material in the form of nucleic acids—the basic molecules of the central dogma. Once in the tissues of a living organism, they don't multiply, but rather affect similar proteins - often in the brain - and behave like role models. Other proteins change to mimic the prion's abnormal shape, converting other natural proteins into that shape. The original prion can be caused by a genetic mutation of the normal PrP protein, by transmission from infected sources such as meat and fungi, or as a spontaneous misfolding event. The latter cause is more likely in Creutzfeldt-Jacob disease in cattle.

However, if - as Francis Crick made clear - you only relate the central dogma to cellular life, it remains true. So far there are no exceptions. Because prions and retroviruses are not cells. Viruses and prions are proteins. They need living organisms to reproduce and do not grow or produce their own energy; they are not "alive". At the genetic level, retrovirusesareliving, because they contain genetic material, they develop and multiply (albeit within a living organism). Prions contain no genetic material and are simply misfolded proteins.

Central dogma and genetic medicine

Crick's core dogma applies to all biological cells (not retroviruses or prions) that contain DNA. To this day, no gene medicine refutes the central dogma. On the contrary, most research follows the assumptions made by Crick almost seventy years ago.

Genetic medicine can be used at various points within the steps of protein synthesis.

• Replication: A piece of DNA is cleaved off to create a copy of the original.
• Transcription: Transferring a piece of replicated DNA (template DNA) to mRNA.
• Splicing: One or more unnecessary sequences (introns) are removed from the immature mRNA. Alternatively, different introns can be removed to produce different mature mRNA molecules.
• Translation: The ribosome reads groups of three sequences (codons) in the mRNA at binding sites. Initiation and elongation factors bring the right matching anticodon of a tRNA molecule to each codon. Each tRNA carries a specific amino acid. Amino acids are linked together to form a polypeptide chain. As the chain moves through the ribosome, the polypeptide chain can begin to fold to produce a functional protein as the code is translated into a foldable protein. Other "companion proteins" are usually needed to help with the folding process; Splicing is also possible at this stage. Spliced ​​parts of a polypeptide or protein are called inteins.

To treat genetic diseases we can intervene in any of the above steps:

• Gene therapy: introducing functional copies of genes to replace non-functional or disease-causing genes with viral vectors (carriers). Unhealthy cells are "infected" with health-promoting genetic information. When the recipient cells divide, the daughter cells contain the modified sequence.
• Gene modification: turn gene transcription on or off. Many genes are only turned on at specific times or in specific cells by regulatory proteins that bind to noncoding regions of that gene's DNA. Repressor or activator proteins bind to these proteins, thereby repressing or activating the expression of that gene.
• RNA Splicing: Certain proteins are sometimes not made due to mutations that block translation. This is called exon skip. For example, cataplexy is the result of exon skipping mutations in the gene that produces a brain-based receptor. RNA splicing can alleviate symptoms caused by exon skipping mutations. Genetic engineers insert a small piece of RNA (antisense RNA) that skips the disease-causing mutation. Although current (initial) research provides short and thus partially functional proteins, there is hope for many hereditary diseases.
• RNA interference: When unwanted proteins are produced, often by overexpression or expression at the wrong time, it is possible to correct this by inserting small interfering RNA (siRNA) or microRNA (miRNA). These bind to a silencing complex and jointly break down corresponding mRNA molecules. This genetic therapy has the potential to silence any gene.

The next step in gene medicine is precision medicine, where disease treatment and prevention takes into account each person's genes, environment and lifestyle. This approach will take time, but it is certainly the future of medicine - the result of a groundbreaking theory from the mid-20th century that will endure well into the next century.

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