Central Dogma: Basics of DNA, RNA, Proteins
Biotechnology
### Central Dogma: Basics of DNA, RNA, and Proteins
The **Central Dogma of Molecular Biology**, formulated by Francis Crick in 1958, describes the directional flow of genetic information within a biological system. It states that information passes from DNA to RNA to protein, and this transfer is generally irreversible.
**DNA: The Master Blueprint**
Deoxyribonucleic acid (DNA) is the long-term storage molecule of genetic information. It consists of two antiparallel polynucleotide strands wound into a double helix. Each nucleotide contains a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G), or cytosine (C). Base pairing is specific: A pairs with T (two hydrogen bonds), and G pairs with C (three hydrogen bonds). The sequence of these bases encodes the instructions for building all cellular proteins. DNA resides primarily in the nucleus (in eukaryotes) and is replicated before cell division.
**RNA: The Messenger and Worker**
Ribonucleic acid (RNA) is typically single-stranded and uses ribose sugar with uracil (U) replacing thymine. Three major classes participate in information transfer:
- **mRNA (messenger RNA):** A complementary copy of a gene, transcribed from DNA. It carries the genetic code from the nucleus to ribosomes in the cytoplasm.
- **tRNA (transfer RNA):** Adaptor molecules that bring specific amino acids to the ribosome during protein synthesis.
- **rRNA (ribosomal RNA):** Catalytic and structural component of ribosomes.
**Proteins: The Functional Executors**
Proteins are polymers of amino acids linked by peptide bonds. The linear amino acid sequence (primary structure) folds into three-dimensional conformations (secondary, tertiary, quaternary) that determine function. Proteins serve as enzymes, structural scaffolds, signaling molecules, transporters, and regulators.
**The Two Key Processes**
1. **Transcription:** DNA is transcribed into RNA by RNA polymerase. A DNA segment (gene) serves as template to synthesize a complementary mRNA strand. In eukaryotes, pre-mRNA undergoes splicing (intron removal, exon joining) to produce mature mRNA.
2. **Translation:** The mRNA sequence is decoded by ribosomes to synthesize a polypeptide chain. Each triplet codon (three nucleotides) specifies one amino acid, following the genetic code—nearly universal and degenerate (multiple codons per amino acid).
The Central Dogma remains foundational, though exceptions exist (e.g., reverse transcription in retroviruses, prion propagation). Nonetheless, DNA → RNA → protein provides the core framework for understanding heredity, gene expression, and cellular function.