Protein SynthesisProtein Synthesis““From code into Flesh From code into Flesh &&

BloodBlood””

Why RNA Synthesis is Why RNA Synthesis is “easier”“easier”

Whole DNA molecule not unwound:Whole DNA molecule not unwound: no single-stranded binding proteinsno single-stranded binding proteins no topoisomeraseno topoisomerase RNA polymerse, not DNA RNA polymerse, not DNA

polymerasepolymerase no primer neededno primer needed still 5’still 5’ 3’ (but no lagging strand, 3’ (but no lagging strand,

no Okazaki fragments)no Okazaki fragments)

Protein Synthesis: Prok Protein Synthesis: Prok vs. Euk vs. Euk

LocationLocation mRNA processingmRNA processing

Fig. 17-3a-1Fig. 17-3a-1

TRANSCRIPTION DNA

mRNA

(a) Bacterial cell

Fig. 17-3a-2Fig. 17-3a-2

(a) Bacterial cell

TRANSCRIPTION DNA

mRNA

TRANSLATIONRibosome

Polypeptide

Fig. 17-3b-1Fig. 17-3b-1

(b) Eukaryotic cell

TRANSCRIPTION

Nuclearenvelope

DNA

Pre-mRNA

Fig. 17-3b-2Fig. 17-3b-2

(b) Eukaryotic cell

TRANSCRIPTION

Nuclearenvelope

DNA

Pre-mRNARNA PROCESSING

mRNA

Fig. 17-3b-3Fig. 17-3b-3

(b) Eukaryotic cell

TRANSCRIPTION

Nuclearenvelope

DNA

Pre-mRNARNA PROCESSING

mRNA

TRANSLATION Ribosome

Polypeptide

mRNA “processing”mRNA “processing”1)1) ““Head” end – “5’ cap” = modified Head” end – “5’ cap” = modified

guanineguanine2)2) ““Tail” end – 3’ “poly-A’ tailTail” end – 3’ “poly-A’ tail3)3) ““splicing” of message!?!splicing” of message!?!

Cut out “introns”Cut out “introns” ““exons” are expressedexons” are expressed

Eukaryotic cells modify RNA Eukaryotic cells modify RNA after transcriptionafter transcription

Three Types of RNAThree Types of RNA mRNAmRNA tRNAtRNA rRNArRNA

All single strandedAll single stranded All transcribed from DNA “genes”All transcribed from DNA “genes” Only mRNA translated into proteinOnly mRNA translated into protein

Fig. 17-14aFig. 17-14a

Amino acidattachment site

(a) Two-dimensional structure

Hydrogenbonds

Anticodon

3

5

Fig. 17-14bFig. 17-14b

Amino acidattachment site

3

3

5

5

Hydrogenbonds

Anticodon Anticodon

(b) Three-dimensional structure(c) Symbol used in this book