Lecture 6: The Genetic code

• Proteins are made by the ribosome which are in the cytoplasm of eukaryotes, but DNA is in the nucleus. DNA doesn’t directly work with the ribosomes but act through an intermediary mRNA.
• The Central Dogma proposed by Crick, Brenner, and Jacob explained how genetic information flows from DNA to RNA to proteins.
• During transcription, RNA polymerase binds to DNA at the beginning of a gene, unwinds the DNA, and synthesizes a complementary RNA strand using ribonucleotides. This process, akin to DNA replication but with RNA as the product, creates mRNA containing the genetic information of the gene. Once synthesized, mRNA leaves the nucleus and enters the cytoplasm, where ribosomes utilize its information to synthesize proteins.
• • RNA polymerase transcribes DNA into mRNA, which carries the information to ribosomes in the cytoplasm for translation into proteins.
• Nirenberg, Matthaei, and Khorana deciphered the genetic code by associating specific nucleotide sequences (codons) with corresponding amino acids. This code is degenerate, with multiple codons coding for the same amino acid, and includes stop codons that signal protein synthesis termination.
• • tRNA acts as an adapter molecule, carrying specific amino acids to ribosomes based on codon-anticodon base pairing. Aminoacyl tRNA synthetases catalyze the attachment of amino acids to tRNA molecules, determining the correspondence between codons and amino acids.
• • tRNA molecules carry amino acids corresponding to their anticodons, binding to mRNA codons. Ribosomes guide tRNA-mRNA interactions, catalyzing peptide bond formation between amino acids carried by tRNAs. This process results in protein synthesis following mRNA sequence.
• This process of converting the information in the mRNA sequence to the protein sequence is called translation.