Protein Synthesis “From code into Flesh & Blood”

Why RNA Synthesis is “easier” Whole DNA molecule not unwound: Whole DNA molecule not unwound:  no single-stranded binding proteins  no topoisomerase RNA polymerse, not DNA polymerase RNA polymerse, not DNA polymerase  no primer needed  still 5’  3’ (but no lagging strand, no Okazaki fragments)

Protein Synthesis: Prok vs. Euk Location Location mRNA processing mRNA processing

Fig. 17-3a-1 TRANSCRIPTION DNA mRNA (a) Bacterial cell

Fig. 17-3a-2 (a) Bacterial cell TRANSCRIPTION DNA mRNA TRANSLATION Ribosome Polypeptide

Fig. 17-3b-1 (b) Eukaryotic cell TRANSCRIPTION Nuclear envelope DNA Pre-mRNA

Fig. 17-3b-2 (b) Eukaryotic cell TRANSCRIPTION Nuclear envelope DNA Pre-mRNA RNA PROCESSING mRNA

Fig. 17-3b-3 (b) Eukaryotic cell TRANSCRIPTION Nuclear envelope DNA Pre-mRNA RNA PROCESSING mRNA TRANSLATION Ribosome Polypeptide

mRNA “processing” 1) “Head” end – “5’ cap” = modified guanine 2) “Tail” end – 3’ “poly-A’ tail 3) “splicing” of message!?!  Cut out “introns”  “exons” are expressed

Eukaryotic cells modify RNA after transcription

Three Types of RNA mRNA mRNA tRNA tRNA rRNA rRNA All single stranded All single stranded All transcribed from DNA “genes” All transcribed from DNA “genes” Only mRNA translated into protein Only mRNA translated into protein

Fig a Amino acid attachment site (a) Two-dimensional structure Hydrogen bonds Anticodon 3 5

Fig b Amino acid attachment site Hydrogen bonds Anticodon (b) Three-dimensional structure (c) Symbol used in this book