4 Transcription: Initiation RNA polymerase attaches to a “promoter” sequence in front (“upstream”) of a geneEukaryotes only: RNA polymerase requires multiple “Transcription factor” proteins to be able to bind to the promoter
16 The Genetic Code Universal across ALL domains of Life! Triplet Code: mRNA is read in units of three adjacent bases (codons)There are 64 possible codons (for 20 amino acids)The code is redundant and unambiguousThe code has “start” and “stop” codons
18 Translation: Initiation mRNA interacts with the ribosome to begin translation at the START codon (AUG) closest to the 5’ end of the mRNAtRNA molecule brings methionine (amino acid coded for by AUG codon)
20 Translation: Elongation Subsequent amino acids are brought to the ribosome by tRNA molecules as specified by subsequent, adjacent codonsEach amino acid is transferred to a growing polypeptide chainPeptide bonds formed between chain and new amino acidEmpty tRNA molecule exits the ribosome and picks up another amino acidREPEAT!!!!
22 Translation: Termination Once a Stop codon is reachedRelease factor protein binds and the polypeptide is released from the ribosomePolypeptide moves to golgi body or cytoplasm for further processingThe ribosome disassembles
23 How does prokaryotic protein synthesis compare to eukaryotic?
24 How does prokaryotic compare to eukaryotic protein synthesis? Transcription: Prokaryotes can bind DIRECTLY to the promoter region (no transcription factors required)No Post-transcription modification of RNAProkaryotes have no nucleus so Transcription and Translation are coupled (occur together) – RNA is transcribed and translated at the same time
25 What is a polyribosome? How do prokaryotic and eukaryotic organisms benefit from them? Many ribosomes translating the same RNA transcriptEnables simultaneous translation of one transcript