Understanding Protein Synthesis: Transcription and Translation Explained

Process where mRNA is decoded and a protein is produced

The process we are referring to is called protein synthesis

The process we are referring to is called protein synthesis. It involves two main steps: transcription and translation.

1. Transcription: It occurs in the nucleus of a eukaryotic cell or the cytoplasm of a prokaryotic cell. During this step, the DNA sequence of a gene is copied into a molecule called messenger RNA (mRNA). The enzyme RNA polymerase initiates transcription by binding to a specific region near the gene called the promoter. Once bound, RNA polymerase unwinds the DNA double helix and synthesizes a complementary RNA strand using one of the DNA strands as a template.

The mRNA molecule is synthesized in the 5′ to 3′ direction and is complementary to the DNA template. However, there are a few differences between DNA and RNA: RNA uses uracil (U) as a base instead of thymine (T), and the sugar in the RNA molecule is ribose instead of deoxyribose. The transcription process continues until RNA polymerase reaches a specific termination sequence on the DNA template. At this point, the mRNA molecule is released and can now exit the nucleus and move into the cytoplasm.

2. Translation: It occurs in the cytoplasm, specifically on ribosomes. Ribosomes are composed of proteins and ribosomal RNA (rRNA) and serve as the site where mRNA is decoded and proteins are synthesized. Translation can be divided into three steps: initiation, elongation, and termination.

– Initiation: It begins when the small ribosomal subunit binds to the mRNA molecule at a specific sequence called the start codon (usually AUG). The start codon codes for the amino acid methionine, which is often the first amino acid in many proteins. The large ribosomal subunit then joins the small subunit, forming a functional ribosome.

– Elongation: During this step, the ribosome moves along the mRNA molecule in a 5′ to 3′ direction, adding amino acids to the growing polypeptide chain. The ribosome recognizes each codon of the mRNA using transfer RNA (tRNA) molecules. Each tRNA carries a specific amino acid and has an anticodon sequence that is complementary to the codon on mRNA. The ribosome facilitates the pairing of the mRNA codon with the tRNA anticodon, allowing the amino acids to come together and form a peptide bond. This process continues until a stop codon is reached.

– Termination: When a stop codon (UAA, UAG, or UGA) is encountered, it signals the termination of translation. Instead of carrying an amino acid, specific release factors bind to the stop codon, causing the tRNA and polypeptide chain to be released from the ribosome. The ribosome then dissociates into its subunits, and the newly synthesized protein is free to fold into its functional conformation or undergo additional modifications.

In summary, the process of protein synthesis involves transcription, where the DNA sequence is transcribed into mRNA, and translation, where the mRNA is decoded on ribosomes to synthesize proteins.

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