Replication, Transcription, and Translation: From DNA to Protein

This post is be a chart comparing the Initiation, Elongation, and Termination stages for Replication, Transcription, and Translation.

	Process
	Replication	Transcription	Translation
Initiation	·      Helicase unzips the DNA double helix ·      Single-strand binding proteins (SSBP) keep unpaired template strands apart during replication ·      Gyrase releases tension brought about by unwinding and twisting the DNA ·      Primase synthesizes a short RNA primer to start DNA synthesis [A=U, C≡G]	·       Starts at TATA box (part of promoter region) ·       Transcription factors (TFs) bind to promoter region ·       RNA Polymerase II binds to TFs to form initiation complex at the promoter region, upstream of the gene ·       *Note: Gene = transcription unit	·       Small ribosomal subunit binds with mRNA and special initiator tRNA carrying methionine which attaches to start codon (AUG) (anticodon on tRNA) ·       Initiation factors bring in large subunit such that tRNA occupies the P site
Elongation	·       DNA Polymerase III synthesizes new DNA strand; reads DNA 3ʹ→5ʹ; makes DNA 5ʹ→3ʹ ·       Leading and Lagging strands on both sides of replication bubble, but with alternate orientations	·       RNA Pol II synthesizes RNA strand; reads DNA template 3ʹ→5ʹ, creating RNA transcript 5ʹ→3ʹ ·       New RNA strand is similar to coding strand	·       Codon recognition: elongation factor assists bonding b/w codon of mRNA under A site with matching anticodon of tRNA carrying amino acid ·       Peptide bond formation: rRNA catalyzes formation of peptide bond b/w polypeptide in P site with new amino acid in A site ·       Translocation: ribosome moves tRNA with attached polypeptide from A site to P site; mRNA moves with tRNA; tRNA at P site is moved to E site and leaves ribosome ·       mRNA is read 5ʹ→3ʹ codon by codon
Termination	·       DNA Polymerase I proofreads new DNA and replaces RNA primers with DNA nucleotides ·       Ligase “glues” the gaps b/w Okazaki fragments by forming phosphodiester bonds	·       AAUAA sequence on RNA (terminator region)(downstream) stops production of RNA; causes new RNA strand to break off and RNA Pol II falls off DNA molecule ·       After transcription: 5ʹ cap is added to 5ʹ end of RNA transcript, consisting of a modified form of guanine; poly-A polymerase adds poly-A tail to 3ʹ end of RNA transcript; also, introns are removed via RNA splicing done by spliceosomes containing snRNPs and snRNA	·       Occurs when stop codon reaches A site (UAA, UAG, UGA) ·       Release factor hydrolyzes bond b/w polypeptide and its tRNA in P site, freeing polypeptide and causing translation complex to disassemble