Describe how DNA is converted, during transcription, into mRNA through initiation, elongation and termination. In addition, describe how RNA is converted to proteins through the steps of initiation, elongation, and termination.
make this bold
how about a <table><tr><td>top</td></tr><hr><tr><td>bottom</td></tr></table> fraction?
During transcription, DNA is converted into mRNA in a process that occurs in the nucleus of the cell. Let's break down the steps of transcription:
1. Initiation: The first step in transcription is initiation. It begins with the enzyme RNA polymerase binding to a specific region of the DNA called the promoter. The promoter serves as a signal for the start of transcription and helps position the RNA polymerase.
2. Elongation: Once the RNA polymerase binds to the promoter, it unwinds the DNA double helix. As it progresses along the DNA strand, the RNA polymerase reads the template strand of the DNA and synthesizes a complementary mRNA molecule. RNA nucleotides, which are present in the nucleus, are assembled into a chain using the DNA template as a guide. The mRNA strand is built in a 5' to 3' direction, and it is complementary to the template DNA strand (except that mRNA contains uracil (U) instead of thymine (T)).
3. Termination: The final step of transcription is termination. When the RNA polymerase reaches a specific sequence of DNA called the terminator, the mRNA transcript is released, and the RNA polymerase detaches from the DNA. The DNA double helix reforms, and the mRNA molecule is now ready to leave the nucleus and travel to the cytoplasm for translation.
Now, let's move on to the steps involved in the conversion of mRNA into proteins through the process of translation:
1. Initiation: The small ribosomal subunit binds to the mRNA molecule near the start codon. The start codon is typically AUG (adenine, uracil, guanine), which codes for the amino acid methionine. The initiator tRNA molecules, carrying methionine, bind to the start codon on the mRNA, allowing the large ribosomal subunit to join the complex and complete the initiation.
2. Elongation: After initiation, the ribosome moves along the mRNA molecule in a 5' to 3' direction, reading the codons (sequences of three nucleotides) of the mRNA. Each codon codes for a specific amino acid. As the ribosome moves, it recruits tRNA molecules that carry complementary anticodons to the exposed codons on the mRNA. The ribosome catalyzes the formation of peptide bonds between successive amino acids carried by the tRNA molecules, forming a growing polypeptide chain.
3. Termination: Translation continues until the ribosome encounters a stop codon (UAA, UAG, or UGA) on the mRNA. When a stop codon is reached, a release factor protein binds to the ribosome, causing the process to terminate. The newly synthesized polypeptide is released from the ribosome, and the ribosome dissociates from the mRNA.
The newly synthesized polypeptide undergoes additional processing, folding, and modifications to become a functional protein within the cell.