How does DNA serve as the master blueprint for building proteins?

DNA (deoxyribonucleic acid) is a double-stranded helical molecule that stores genetic information in the form of nucleotide sequences. Each nucleotide is made up of a sugar group, a phosphate group, and a nitrogenous base. There are four nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). The bases on one strand of DNA pair with the bases of the other strand (A with T, and G with C) through hydrogen bonds. This base pairing ensures that the genetic information is conserved during replication and provides the template for protein synthesis.

Transcription is the first step in protein synthesis, during which a section of the DNA molecule is copied into a molecule called messenger RNA (mRNA). This process involves three main stages: 1. Initiation: The enzyme RNA polymerase attaches to a specific site on the DNA called the promoter region and begins to unwind and separate the two DNA strands. 2. Elongation: RNA polymerase reads one strand of the DNA (known as the template strand) from 3' to 5' direction and synthesizes the mRNA molecule in a 5' to 3' direction by incorporating the complementary RNA nucleotides: Adenine pairs with Uracil (U), and Guanine pairs with Cytosine. 3. Termination: When the RNA polymerase reaches a termination signal on the DNA template, it detaches, and the newly created mRNA molecule is released.

In eukaryotic cells, the newly formed mRNA undergoes various modifications before leaving the nucleus: 1. Addition of the 5' cap: A guanosine molecule is added to the 5' end of the mRNA to protect it from degradation and help it bind to the ribosome. 2. Polyadenylation (adding the poly-A tail): A series of adenine nucleotides are added to the 3' end of the mRNA molecule to protect it from degradation and help in ribosome binding as well. 3. Splicing: Introns (non-coding regions) are removed from the mRNA sequence, and exons (coding regions) are joined together to form the final, mature mRNA molecule. After processing, the mature mRNA molecule is exported from the nucleus to the cytoplasm.

Translation is the process of building a protein based on the genetic information carried by the mRNA molecule. Translation occurs on ribosomes present in the cytoplasm and involves three main stages: 1. Initiation: The ribosome binds to the 5' end of the mRNA molecule and scans the mRNA until it encounters the start codon (usually AUG). A transfer RNA (tRNA) molecule, carrying the matching amino acid and the appropriate anticodon, then binds to the start codon. 2. Elongation: The ribosome reads the mRNA codons (three nucleotide sequences that specify an amino acid) and matches them up with the respective tRNA carrying the appropriate amino acids. The amino acids are then linked together through peptide bonds to form the growing polypeptide chain. 3. Termination: When the ribosome encounters a stop codon (UAA, UAG, or UGA) on the mRNA, no tRNA can bind to it. Instead, a release factor binds to the stop codon, and the ribosome releases the completed polypeptide chain. In conclusion, DNA serves as a master blueprint for building proteins through a process involving transcription and translation. The specific sequences of nucleotide bases in DNA provide the basis for encoding proteins, ultimately determining an organism's traits and functions.