Chapter 8: Transcription and RNA processing Fig. 8-1

Fundamental chemical distinctions of DNA and RNA 2’ carbon Methyl in thymine pp. 257-8

Fig. 8-3

General types of RNA Informational: mRNA (most diverse) Functional: tRNA rRNA (most abundant) snRNA scRNA

Transcription (DNA-dependent RNA synthesis) Requirements: RNA polymerase template DNA (one strand) ribonucleoside triphosphates (ATP, GTP, CTP, UTP) assorted cofactors (e.g., Mg++) Directionality: RNA always synthesized 5'3' template DNA is read 3' 5' RNA is complementary to its template DNA

Types of RNA polymerase Prokaryotes: single enzyme complex Eukaryotes: three types Pol I transcribes rRNA genes Pol II transcribes mRNA genes Pol III transcribes tRNA, some snRNA genes

Genes may be transcribed from either DNA strand (may be divergently transcribed) Fig. 8-4

Fig. 8-5

Transcription of rDNA genes in amphibian oocyte Fig. 8-6

Polarity and complementarity of DNA and RNA strands Fig. 8-7

Prokaryote 5’-ends & consensus sequences Fig. 8-8

Prokaryote transcription initiation Fig. 8-9

Post-initiation transcription steps Fig. 8-10

Example of a prokaryotic transcription terminator (a hairpin loop structure) Fig. 8-11

Eukaryotic transcription initiation requires the ordered assembly of a preinitiation complex (general transcription factors) (includes specific transcription factors) Fig. 8-12

Pre-mRNA processing in eukaryotes 5’ cap addition (7-methylguanosine addition by guanyltransferase) Splicing to remove introns

Fig. 8-13

Pre-mRNA splicing in eukaryotes Spliceosome: a ribonucleoprotein complex consisting of snRNAs + proteins + pre-mRNA Highly conserved RNA sequences at the intron/exon boundaries  Recruit snRNAs and proteins that assemble into the spliceosome complex Highly ordered, sequential series of reactions cleave away intron and join together the flanking exons

Common elements of an intron that direct proper splicing Fig. 8-15

Fig. 8-16

Differential splicing creates diverse mRNAs from a single gene Fig. 8-14

Pre-mRNA processing in eukaryotes 5’ cap addition (7-methylguanosine addition by guanyltransferase) Splicing to remove introns 3’ polyadenylation - Endonuclease cleavage of pre-mRNA ~20 nucleotides 3’ to AAUAAA - Addition of up to several hundreds of A’s to 3’ end by poly(A) polymerase

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