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Eukaryotic Gene Expression
The “More Complex” Genome
genome characteristics differ dramatically
Table 14.1
E. coli and yeast, the “eukaryotic E. coli”
Table 14.2
Table 14.3
Table 14.4
The Eukaryotic Genome•prokaryotic and eukaryotic genomes encode many of the same functions
•eukaryotes encode additional functions associated with organelles
•genomes of multicellular eukaryotes encode additional functions
•each eukaryotic kingdom encodes specialized products–so, eukaryotic genomes are larger–but why so much?
Genomes Vary in SizeOrganism Genome Size (bp) Genes
E. coli 4,460,000 (h) 4,300
Yeast 24,136,000 6,200
Nematode 97,000,000 19,099
Fruit fly 180,000,000 13,600
Puffer fish 365,000,000 ~30,000
Human 6,200,000,000 22,000
Arabidopsis 119,000,000 15,000 (26,000)
Rice 389,000,000 37,544
Lily 600,000,000,000 ??????????????
Table 14.5
The Eukaryotic Genome•Genomics –analyzes and compares entire genomes of different organisms
–sequences of many genomes are complete
•Proteomics –analyzes and compares the functions of the proteins in an cells, tissues, organs, organisms
The Eukaryotic Genome•repetitive DNA sequences–highly repetitive sequences (103 - 106 each)•tandemly repeated satellites (5-50 bp)–mainly at centromeres
•minisatellites (12-100 bp)–Variable Number Tandem Repeats
•microsatellites (1-5 bp x 10-50)–small, scattered clusters
•untranslated
Figure 11.18
rRNA genes are tandemly repeated
Figure 14.2
The Eukaryotic Genome
•repetitive DNA sequences–moderately repetitive sequences•telomeres (~2500 x TTAGGG per chromosome end - human)•clustered tRNA, rRNA genes (~280 rRNA coding units on 5 chromosomes - human)•transposable elements (transposons)
The Eukaryotic Genome•transposable elements (transposons)–SINES: transcribed elements ~500 bp long
–LINES: elements ~7000 bp long; some are expressed•>100,000 copies•retrotransposition
–retrotransposons: like retroviral genomes
–DNA transposons: translocating DNAs
Figure 14.3
gene expressi
on in
eukaryotes
Figure 14.1
The Eukaryotic Genome•Gene expression –protein-coding genes•contain non-coding sequences–promoter–terminator–introns interrupt the coding sequence found in exons
•the primary transcript is processed to produce an mRNA
eukaryotic genes contain non-coding regionsFigure 14.4
Figure 14.5
DNA-mRNA hybrids revealedthe
presence of
intronsFigure 14.6
capping tailing
the ends of primary transcripts are processedFigure 14.9
The Eukaryotic Genome•Gene expression –protein-coding genes •primary transcripts are processed to produce mRNAs primary transcripts are processed to produce mRNAs–the 5’ end is capped with reversed GTP–the 3’ end is given a “poly (A)” tail at the polyadenylation site, AAUAAA–introns are removed during splicing by snRNPs of the spliceosome
introns are
removed from
primary transcripts
byspliceosomesFigure 14.10
regulation of
eukaryotic gene
expression may occur at many different points
Figure 14.11
transcriptionfactorsassist RNA
polymerase to bind to the promoter
Figure 14.12
The Eukaryotic Genome•expression of eukaryotic genes is highly regulated–three different RNA polymerases transcribe different classes of genes
–each RNA polymerase binds to a different class of promoters
–RNA polymerases require transcription factors in order to bind to their promoters
–transcriptional activators may bind far from the promoter
DNA elements are binding sites for proteins of the transcription machinery
Figure 14.13
DNA looping can bring distant protein factors into contact with the promoter complex
Figure 14.13
The Eukaryotic Genome•expression of eukaryotic genes is highly regulated–eukaryotes do not group genes with related functions together in operons
–genes that are coordinately expressed share DNA elements that bind the same transcriptional regulator proteins
common response elements enable coordinated expression of independentgenesFigure 14.14
gene regulators bind to DNA elements
•common motifs are found among gene regulators
Figure 14.15
The Eukaryotic Genome
•many genes are present in single copies–some genes are present in a few similar copies in “gene families”•one or more expressed, functional genes•non-functional pseudogenes
nonfunctional pseudogenes
human globin genes are found in
two gene familiesFigure 14.7
changes in expression of alternate globin genes
Figure 14.8
transcription factors remodel chromatin to bind promotersFigure 14.16
The Eukaryotic Genome
•DNA is packaged as chromatin in the nucleus–transcription factors remodel chromatin to bind promoters•condensed DNA can “turn off” entire regions of chromosomes
The Eukaryotic Genome
•one gene can encode more than one polypeptide–some primary transcripts undergo alternative splicing
alternate splicing: multiple polypeptides from single genes
Figure 14.20
The Eukaryotic Genome
•proteins are ultimately removed, degraded and replaced–the proteasome degrades proteins that are tagged for degradation
the proteasome recognizes ubiquitin-bound polypeptides
Figure 14.22