Transcriptin And Translation I,E,T Flashcards
Initiation of Transcription
Initiation of Transcription
RNA polymerase binds to the promoter region of the DNA.
In eukaryotes, transcription factors assist in RNA polymerase binding.
The DNA helix unwinds, exposing the template strand for RNA synthesis.
The first RNA nucleotide is added complementary to the DNA template (using uracil instead of thymine).
Elongation of Transcription
RNA polymerase moves along the DNA template strand, synthesizing the RNA molecule in the 5’ to 3’ direction.
The RNA strand is complementary to the DNA template strand (A-U, C-G, G-C, T-A).
DNA rewinds behind the RNA polymerase as the RNA transcript is being synthesized.
Termination of Transcription
Transcription continues until a specific termination signal is reached (e.g., a terminator sequence or a hairpin loop in prokaryotes).
In eukaryotes, the RNA is cleaved at a specific sequence, and RNA polymerase dissociates from the DNA.
Initiation of Translation
The small ribosomal subunit binds to the mRNA at the 5’ cap (in eukaryotes).
The start codon (AUG) is recognized, and the initiator tRNA (carrying methionine in eukaryotes, binds to the start codon.
The large ribosomal subunit joins to form a functional ribosome, completing the initiation complex.
Elongation of Translation
The ribosome moves along the mRNA in the 5’ to 3’ direction, reading codons and adding the corresponding amino acids.
tRNA molecules with attached amino acids enter the ribosome’s A site, match their anticodons to the mRNA codons.
The amino acid is transferred to the growing polypeptide chain at the P site.
The ribosome shifts one codon down the mRNA (translocation), moving the empty tRNA to the E site, where it exits.
Termination of Translation
The ribosome reaches a stop codon (UAA, UAG, or UGA).
Release factors bind to the stop codon, triggering the release of the polypeptide chain from the tRNA.
The ribosomal subunits dissociate, and the mRNA is released.
