Definition of Central Dogma
A Central Dogma describes how DNA is converted to RNA and then into Proteins in Molecular Biology. A genomic process refers to the conversion of DNA information into a functional product.
RNA serves as a messenger to carry information through the Ribosomes as DNA provides instructions for making Proteins.
The Central Dogma is the biological process that transfers Genetic information from DNA to RNA, and then into Proteins.
What is the Central Dogma?
A Central Dogma is an explanation of the flow of Genetic information in a cell, including the replication of the DNA, the transcription of the RNA, and the translation of the RNA to create the Proteins.
It is possible to understand the concept of interaction through the framework. For example, biopolymers are common. Biopolymers are primarily composed of Proteins, RNA, and DNA, which can further be divided into general and unknown transfers.
In the laboratory, special transfers are made in exceptional cases. Cells are generally transferred by general means. Information is constantly flowing through transcription and translation in the human body. It is believed that unknown transfers never occur.
As a result, two new strands of DNA are created, one strand from the parent DNA and one from the newly synthesized DNA. This is called semiconservative DNA replication.
Steps of the Central Dogma
The central dogma takes place in two tages:
1. Transcription
The enzyme RNA Polymerase transfers information from one strand of DNA to another strand of RNA during transcription. Three parts of the DNA strand are involved in this process: the promoter, the structural gene, and the terminator.
DNA strands that synthesize RNA are called template strands, and DNA strands that Code for RNA are called coding strands. RNA polymerases that are DNA-dependent bind to the promoter and catalyze the 3' to 5' directions of polymerization.
The newly synthesized RNA strand is released from the terminator sequence as it approaches the terminator. RNA strands released after transcription undergo further modifications post-transcriptionally.
2. Translation
Proteins are enCoded by RNA by a process called translation. Translation involves energy and is an active process. The energy comes from the charged tRNA Molecules.
The translation process is initiated by ribosomes. Ribosomes are made up of two subunits, one larger and one smaller. As a result, the larger subunit consists of two tRNA Molecules positioned together so that enough energy can be expended to form a peptide bond.
The mRNA enters the smaller subunit and is then held by the tRNA Molecules present in the larger subunit that are complementary to the codon. In this way, two codons are held together by two tRNA Molecules placed close together and a peptide bond is formed between them. This process results in long polypeptide chains of amino acids.
Genetic Code
Proteins are manufactured from RNA and their Genetic Code contains information about them. In general, three nucleotides and four nitrogenous bases collectively Code for an amino acid, forming a triplet codon. As a result, there are 64 amino acids possible, including 4 x 4 x 4 amino acids. There are 20 amino acids found naturally.
As a result, the Genetic Code deteriorates. Due to the characteristics of the Genetic Code, some amino acids are enCoded by more than one codon at a time, causing the amino acid to degenerate. There is only one codon for each amino acid and the Code is universal regardless of the organism.
In total, there are 64 codons, of which three are stop codons that end transcription and one is an initiator codon, i.e. AUG, which Codes for methionine.
FAQs on Central Dogma of Molecular Biology
1. What is the central dogma of molecular biology, and who first proposed it?
The central dogma of molecular biology is a fundamental principle that describes the flow of genetic information within a biological system. It was first proposed by Francis Crick in 1958. The dogma states that genetic information flows unidirectionally from DNA to RNA (through transcription) and then from RNA to Protein (through translation).
2. What are the three core processes that define the central dogma?
The central dogma is built upon three major processes that manage and express genetic information:
- Replication: The process where a DNA molecule is copied to produce two identical DNA molecules, ensuring genetic continuity during cell division.
- Transcription: The synthesis of a messenger RNA (mRNA) molecule from a DNA template. This step transfers the genetic instructions from the nucleus to the cytoplasm.
- Translation: The process where the genetic code carried by mRNA is read by ribosomes to synthesise a specific protein, turning the genetic blueprint into a functional product.
3. In a eukaryotic cell, where do transcription and translation take place?
In eukaryotic cells, the processes are spatially separated. Transcription, the creation of RNA from DNA, occurs within the nucleus, where the cell's genetic material is stored. The newly formed mRNA molecule is then processed and exported to the cytoplasm, where translation occurs on the ribosomes.
4. Why is the expression of a gene through the central dogma a two-step process (transcription and translation)?
Using an mRNA intermediate provides two key advantages for the cell. Firstly, it protects the original DNA blueprint from potential damage by keeping it safely inside the nucleus. Secondly, it allows for amplification of the genetic signal; a single gene can be transcribed into many mRNA molecules, each of which can be translated multiple times, enabling the rapid production of large quantities of protein when needed.
5. How does the central dogma process differ between prokaryotic and eukaryotic cells?
The primary difference lies in the cellular location and timing. In eukaryotes, the presence of a nucleus separates transcription (in the nucleus) from translation (in the cytoplasm). In prokaryotes, which lack a nucleus, there is no such barrier. As a result, transcription and translation are coupled processes, meaning translation can begin on an mRNA molecule while it is still being synthesised from the DNA template.
6. What are the different roles of mRNA, tRNA, and rRNA within the central dogma?
While the central dogma often simplifies the flow to 'RNA', different types of RNA have specialised roles:
- mRNA (messenger RNA): Acts as the 'messenger' by carrying the genetic code from the DNA in the nucleus to the ribosome.
- tRNA (transfer RNA): Acts as the 'adapter' molecule. It reads the codons on the mRNA and brings the corresponding specific amino acid to the ribosome to be added to the growing protein chain.
- rRNA (ribosomal RNA): Is a structural and catalytic component of ribosomes, the machinery responsible for protein synthesis. It helps align the mRNA and tRNA and catalyses the formation of peptide bonds.
7. How does reverse transcription challenge the original concept of the central dogma?
Reverse transcription is a major exception to the unidirectional flow proposed by Crick. This process, carried out by the enzyme reverse transcriptase, synthesises DNA from an RNA template (RNA → DNA). It is famously used by retroviruses like HIV to insert their genetic information into the host genome. This discovery showed that genetic information can flow backward, adding a layer of complexity to the original central dogma.
8. Does the central dogma always result in a functional protein as the end product?
No, not always. While protein synthesis is a major outcome, some genes are transcribed into functional RNA molecules that are not translated into proteins. These include ribosomal RNA (rRNA) and transfer RNA (tRNA), which are essential for the process of translation itself. Other non-coding RNAs also play critical roles in gene regulation, acting as the final functional product of a gene.
9. What is the importance of the genetic code in the central dogma's pathway?
The genetic code is the universal 'language' that allows the cell to convert the nucleotide sequence of an mRNA molecule into the amino acid sequence of a protein. During translation, the ribosome reads the mRNA in three-nucleotide units called codons. Each codon specifies a particular amino acid or a stop signal. Without this set of rules, the information in RNA could not be accurately translated into a functional protein.
10. What are some examples of how understanding the central dogma is applied in medicine?
Understanding the central dogma is vital for modern medicine. For instance:
- Antiviral drugs: Many HIV treatments work by inhibiting reverse transcriptase, directly blocking the 'RNA → DNA' step of the viral life cycle.
- Antibiotics: Certain antibiotics, like tetracycline and erythromycin, target bacterial ribosomes to disrupt translation, preventing bacteria from producing proteins essential for their survival.
- Gene Therapy: Advanced medical treatments aim to correct genetic diseases by altering the DNA or its expression, directly intervening in the central dogma to produce a missing or functional protein.
