From DNA to Protein: The Synthesis Journey

DNA transcription occurs in the cell nucleus, where DNA serves as the master blueprint for creating RNA.The process begins when RNA polymerase recognizes and binds to a specific DNA sequence called the promoter.RNA polymerase then begins to unzip the DNA double helix, separating the two strands.Using one DNA strand as a template, RNA polymerase builds a complementary messenger RNA strand, following specific base-pairing rules.Notice that in RNA, uracil pairs with adenine instead of thymine, while other base-pairing rules remain the same.As transcription continues, the RNA strand grows longer, creating a working copy of the gene that will eventually leave the nucleus.With the messenger RNA transcript complete, the cell prepares for the next stage of gene expression.The newly transcribed messenger RNA undergoes several important modifications before it can leave the nucleus.First, a special cap is added to the five-prime end of the RNA. This cap protects the RNA from degradation and helps ribosomes recognize where to start.At the three-prime end, a string of adenine nucleotides is added, forming what's called the poly-A tail. This tail also protects the RNA and helps it exit the nucleus.In eukaryotic cells, the RNA contains non-coding regions called introns that must be removed. This process is called RNA splicing.A complex of proteins and RNA called the spliceosome identifies and removes the introns.The remaining exons are joined together to form the mature messenger RNA.The mature messenger RNA can now pass through nuclear pores in the nuclear membrane to enter the cytoplasm.In the cytoplasm, ribosomes are ready to begin translating the messenger RNA into protein.In the cytoplasm, the ribosome assembles around the messenger RNA to begin protein synthesis.The ribosome reads the mRNA sequence in three-letter codes called codons. The first codon, AUG, is the start codon.When the ribosome reaches the stop codon UAA, protein synthesis ends and the completed polypeptide chain is released.The polypeptide chain then folds into its final three-dimensional structure, creating a functional protein.