18. Explain the Central Dogma of Molecular Genetics.
The Central Dogma of Molecular Genetics is a fundamental principle in molecular biology that describes the flow of genetic information within a cell. It explains how genetic information is transcribed from DNA to RNA and then translated into proteins.
To understand the Central Dogma, let's break it down into its three main steps:
1. Transcription: The first step is the transcription, during which genetic information is copied from DNA into RNA. To transcribe a gene, the double-stranded DNA molecule unwinds, exposing one of its strands as a template. An enzyme called RNA polymerase then builds a complementary RNA molecule by incorporating nucleotides that match the corresponding bases on the DNA template strand. This process proceeds along the DNA molecule until the entire gene is transcribed into a single-stranded RNA molecule known as messenger RNA (mRNA).
2. RNA Processing: After transcription, the mRNA molecule undergoes several modifications, collectively known as RNA processing. These modifications include the addition of a protective cap at the 5' end and a poly-A tail at the 3' end, as well as the removal of non-coding regions called introns. These modifications help stabilize the mRNA molecule and facilitate its export from the nucleus to the cytoplasm.
3. Translation: The final step of the Central Dogma is translation, where the mRNA molecule is used as a template to direct the synthesis of a protein. The mRNA is read in sets of three nucleotides, called codons. Each codon corresponds to a specific amino acid, and a sequence of codons determines the order in which amino acids are joined together to form a protein. Transfer RNA (tRNA) molecules, each carrying a specific amino acid, recognize the codons on the mRNA and bring the corresponding amino acids to the site of protein synthesis, the ribosome. The ribosome catalyzes the formation of peptide bonds between adjacent amino acids, resulting in the synthesis of a protein.
Overall, the Central Dogma explains the sequential flow of genetic information: DNA is transcribed into mRNA, which is then translated into proteins. This process is crucial for the precise replication, expression, and regulation of genes, and it forms the basis of how genetic information is transferred and utilized in cells.