TranscriptionPage 319-324

Example problems: Page 324, #2,3,9

TranscriptionThe process of making…

RNA reviewVery similar to DNA except:

Has a ribose sugar instead of a deoxyribose

Uses the base uracil instead of thymine

Is generally single-stranded

Video

Transcription Video

Types of RNAmRNA: messenger RNA

tRNA: transfer RNA

rRNA: ribosomal RNA

Steps of Transcription1. Initiation

2. Elongation

3. Termination

RNA PolymeraseThe enzyme responsible for making RNA

In prokaryotes:Only 1 RNA polymerase

In eukaryotes:RNA Polymerase II: responsible for…RNA Polymerase I and III: responsible for…

Transcription InitiationWhat happens?

Promoter: Generally high in A’s and T’s…WHY?

TATA box

TATAAT

Transcription InitiationPromoter:

promoter transcription region termination sequence

gene

Transcription Initiation

+1positive numbersnegative numbers

upstream downstream

start transcription

Transcription Elongation5’ 3’

Template strand

2. Transcription Elongation

Antisense strand:

Sense strand:

5’ A T T A C G A T C T G C A C A A G A T C C T 3’

5’ A U U A C G A U C U G C A C A A G A U C C U 3’

3’ T A A T G C T A G A C G T G T T C T A G G A 5’SENSE STRANDANTISENSE STRAND

DNADNA

mRNA

Transcription Bubble

3. Transcription TerminationTermination sequence

Termination sequences differ between prokaryotes and eukaryotes

Post-transcriptional modificationsPrimary transcript

Modifications are done to stabilize and protect the RNAPoly(A) tail:

Enzyme?

5’ cap: Enzyme? Unusual 5’-to-5’ triphosphate linkage

4. Posttranscriptional Modification

5’ 3’

5’ cap added by capping enzyme complex

primary transcript

3’ poly-A tail added by poly-A polymerase

AAAAAAA

mG

mG

Post-transcriptional modificationsSplicing;

exons – expressed

introns – interfering

4. Posttranscriptional Modification

AAAAAAAmGexon exon exonintron intron intron intron

introns removed by spliceosome proteins

AAAAAAAmG

exon exon exonmRNA transcript

4. Posttranscriptional ModificationSpliceosomes are a series of small nuclear

ribonucleoproteins (snRNP)

snRNPs:cuts out intron sequencessplices exon sequences together