Protein biosynthesis 04/25/2023 by TDLV The Central Dogma of Life replication 04/25/2023 by TDLV Protein Synthesis • Genetic information: the form of specific sequences of nucleotides along the DNA strands • The DNA inherited leads to specific traits by dictating the synthesis of proteins • Protein Synthesis: includes two stages: transcription and translation 04/25/2023 by TDLV Transcription and Translation • Transcription – the synthesis of RNA under the direction of DNA – Produces messenger RNA (mRNA) • Translation – the actual synthesis of a polypeptide under the direction of mRNA – Occurs on ribosomes 04/25/2023 by TDLV Transcription and Translation • In prokaryotes, transcription & translation occur together TRANSCRIPTION DNA mRNA Ribosome TRANSLATION Polypeptide 04/25/2023 (a) Prokaryotic cell In a cell lacking a nucleus, mRNA produced by transcription is immediately translated without additional processing by TDLV Transcription and Translation • In a eukaryotic cell, the nuclear envelope separates transcription from translation • Extensive RNA processing occurs in the nucleus Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA Ribosome TRANSLATION (b) Eukaryotic cell The nucleus provides a separate compartment for transcription The original RNA transcript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA Polypeptide 04/25/2023 by TDLV Transcription • Product/catalysis/materials/ steps • Transcription is the DNAdirected synthesis of mRNA • RNA synthesis – catalyzed by RNA polymerase – Follows the same base-pairing rules as DNA, except that in RNA, uracil substitutes for thymine 04/25/2023 by TDLV TRANSCRIPTION - OVERVIEW  Transcription - when a cell requires a particular protein  specific mRNA synthesized - first, a section of DNA containing the gene unwinds - only one of the DNA strands copied (at the initiation point: sequence TATAAA) - RNA polymerase: moves along DNA template in the 3’-5’direction  replicates DNA sequence into a complementary sequence of mRNA - mRNA synthesized using complementary base pairing with uracil (U) replacing thymine (T)  moves out of the nucleus to ribosomes in the cytoplasm, acts as the template for protein biosynthesis (translation) and the DNA re-winds  released at the termination point RNA • Types/functions • RNA is single stranded, not double stranded like DNA • RNA is short, only gene long, where DNA is very long and contains many genes • RNA uses the sugar ribose instead of deoxyribose in DNA • RNA uses the base uracil (U) instead of thymine (T) in DNA 04/25/2023 by TDLV Synthesis of an RNA Transcript • The stages of transcription: – Initiation – Elongation – Termination 04/25/2023 by TDLV 10