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Central Dogma — Protein Synthesis

Protein synthesis is a fundamental biological process that involves using the information stored in DNA to create new proteins for cells. It follows a series of steps, starting with the transcription of DNA onto mRNA, then the translation of mRNA into an amino acid chain, and finally the folding of the amino acid chain into a functional protein. This process is referred to as the central dogma of biology because of its crucial role in understanding how living organisms function.

Ribonucleic Acids

Ribonucleic acids are the blueprints of biology and come in two primary forms, RNA and DNA. DNA consists of two sugar-phosphate backbones arranged in a double helix, with nucleotide pairs forming the rungs. The four possible nucleotides are Adenine, Thymine, Guanine, and Cytosine, which always bond in specific pairs (G↔C and A↔T).

RNA is similar to DNA, except it has a single backbone with a single row of nucleotides and replaces Thymine with Uracil for chemical reasons. RNA uses oxy ribose sugar in its backbone instead of deoxyribose sugar used in DNA.

Transcription

Transcription is the process of copying the DNA in the nucleus onto a blank mRNA. The DNA double helix is first split in half by the enzyme helicase. RNA polymerase then moves down the chain (in a 5' → 3' direction) and places mRNA nucleotides that are complimentary to the DNA strand. The DNA is spliced together once more, and transcription of the new mRNA strand is complete.

Translation

After transcription, the mRNA leaves the nucleus and enters a ribosome where the translation process begins. Every three bases of the mRNA encode a single amino acid, forming codons. In the ribosome, tRNA with matching anticodons lines up the correct amino acids based on the mRNA's genetic code. Peptide bonds form between the amino acids, creating a polypeptide chain, which exits the ribosome and is ready for folding.

Folding

After exiting the ribosome, the protein moves through the endoplasmic reticulum and the Golgi body. Hydrogen bonds and other chemical reactions cause the polypeptide chain to form its secondary structure, which can be an alpha-sheet or beta-helix. Polar action can bend or twist the protein into a tertiary structure, with hydrophobic and hydrophilic areas attracting similar areas to pull and push the structure. Some proteins have a quaternary structure created by multiple tertiary structures joining together, completing the final protein.

Mutations

Mutations occur when something goes wrong during protein synthesis, leading to a corrupted or damaged protein. Swapping a nucleotide results in a point mutation, changing a single amino acid in the protein. Such mutations can be silent, missense or nonsense, depending on whether they change the resulting amino acid or not. Adding or removing a nucleotide leads to a frameshift mutation, offsetting the entire sequence and disrupting the entire protein.