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BIOCHEmISTRY ``BIOCHEMISTRY—MOlECUlAR BIOCHEmISTRY ``BIOCHEMISTRY—MOlECUlAR SECTION II 41
Functional Enhancer/
organization of a silencer Promoter 5´ UTR Open reading frame 3´ UTR Silencer
eukaryotic gene Exon Intron Exon Intron Exon
DNA 5´ CAAT TATAAT GT AG GT AG AATAAA 3´
ATG start codon Stop
CAAT Box TATA Box
Transcription start Polyadenylation signal
Transcription
Exon Intron Exon Intron Exon
2 Pre-mRNA 2 GU AG GU AG
Splicing
Protein coding region
3 Mature 3 AAAAAA
mRNA
5´ cap
Poly-A tail
Translation
4 Protein 4
Regulation of gene expression
Promoter Site where RNA polymerase II and multiple Promoter mutation commonly results in
other transcription factors bind to DNA dramatic in level of gene transcription.
upstream from gene locus (AT-rich upstream
sequence with TATA and CAAT boxes).
Enhancer DNA locus where regulatory proteins Enhancers and silencers may be located close to,
(“activators”) bind, increasing expression of a far from, or even within (in an intron) the gene
gene on the same chromosome. whose expression they regulate.
Silencer DNA locus where regulatory proteins
(“repressors”) bind, decreasing expression of a
gene on the same chromosome.
RNA processing Initial transcript is called heterogeneous nuclear mRNA is transported out of nucleus to be
(eukaryotes) RNA (hnRNA). hnRNA is then modified and translated in cytosol.
becomes mRNA. mRNA quality control occurs at cytoplasmic
The following processes occur in the nucleus: processing bodies (P-bodies), which contain
Cap Coding Capping of 5′ end (addition of exonucleases, decapping enzymes, and
5'
G ppp 7-methylguanosine cap) microRNAs; mRNAs may be degraded or
3' Polyadenylation of 3′ end (≈ 200 As) stored in P-bodies for future translation.
HO-AAAAA Splicing out of introns Poly-A polymerase does not require a template.
Tail
Capped, tailed, and spliced transcript is called AAUAAA = polyadenylation signal.
mRNA.
FAS1_2019_01-Biochem.indd 41 11/7/19 3:16 PM
