What two steps are involved in the transfer of information from a gene to the final protein product?
The transfer of information from a gene to the final protein product involves two main steps: transcription and translation.
1. Transcription: It is the first step in the transfer of genetic information, where the DNA sequence of a gene is synthesized into a complementary RNA molecule. Transcription takes place in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells. Here's how transcription occurs:
a. Initiation: Enzymes called RNA polymerases bind to the promoter region in DNA near the beginning of the gene. The DNA strands separate, and one of the strands acts as a template for the synthesis of RNA.
b. Elongation: The RNA polymerase moves along the DNA template strand in a 3' to 5' direction and adds complementary RNA nucleotides (A, U, G, and C) to the growing RNA molecule. Adenine (A) in DNA is replaced by uracil (U) in RNA.
c. Termination: The RNA polymerase reaches a termination sequence in the DNA, which signals the end of transcription. The RNA molecule, known as the primary transcript or pre-mRNA, is released.
2. Translation: It is the second step in the transfer of genetic information, where the RNA molecule is used as a template to synthesize a specific sequence of amino acids, forming a protein. Translation occurs in the cytoplasm. Here's how translation occurs:
a. Initiation: The ribosome, composed of two subunits, binds to the mRNA at a specific start codon (usually AUG). Transfer RNA (tRNA) molecules, carrying specific amino acids, enter the ribosome and recognize the codons on the mRNA through complementary base pairing.
b. Elongation: The ribosome moves along the mRNA in a 5' to 3' direction, and tRNA molecules bring the corresponding amino acids according to the codons on the mRNA. The ribosome catalyzes the formation of peptide bonds between the amino acids, creating a chain called the polypeptide. The ribosome moves from one codon to the next, allowing the polypeptide to grow.
c. Termination: When the ribosome reaches a stop codon (UAA, UAG, or UGA) on the mRNA, it signals the end of translation. The polypeptide is released from the ribosome, and the mRNA, ribosome, and tRNA dissociate.
By going through these two steps, the genetic information encoded in DNA is transcribed into RNA and then translated into a protein, which carries out various functions in the cell.