Download The Eukaryotic Genome and Its Expression

David Sadava H. Craig Heller Gordon H. Orians
William K. Purves David M. Hillis
Biologia.blu
B – Le basi molecolari della vita e
dell’evoluzione
The Eukaryotic Genome
and Its Expression
The Eukaryotic Genome and Its Expression
• What are the characteristics of the eukaryotic
genome?
• How are eukaryotic gene transcripts processed?
• How is eukaryotic gene transcription regulated?
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
?
Key differences between eukaryotic and
prokaryotic genomes:
• eukaryotic genomes are larger;
• eukaryotic genomes have more
regulatory sequences;
• much of eukaryotic DNA is non-coding.
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
?
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
?
• Eukaryotes have multiple chromosomes.
• In eukaryotes, translation and
transcription are physically separated
which allows many points of regulation
before translation begins.
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
?
Eukaryote model organisms:
• yeast, Saccharomyces cerevisiae;
• nematode (roundworm), Caenorhabditis
elegans;
• fruit fly, Drosophila melanogaster;
• thale cress, Arabidopsis thaliana.
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
Eukaryotic mRNA is transcribed in the
nucleus but translated in the cytoplasm
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
?
Eukaryote genomes have two types of
highly repetitive sequences that do not
code for proteins:
• minisatellites: 10–40 bp, repeated
several thousand times. Number of
copies varies among individuals—
provides molecular markers;
• microsatellites: 1–3 bp, 15–100 copies.
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
?
Other moderately repetitive sequences
can move from place to place in the
genome - transposons.
Transposons make up 40 percent of
human genome, only 3–10 percent in
other sequenced eukaryotes.
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
DNA transposons and transposition
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
?
The function of the transposons is unclear.
They may be cellular parasites.
If a transposon is inserted into a coding region,
a mutation results. If it’s in a somatic cell,
cancer can result.
Transposons can carry genes to new
locations—adding to genetic variation.
Transposons may have played a role in
endosymbiosis: genes from the onceindependent prokaryotes may have moved to
the nucleus by DNA transposons.
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
Transcription of an eukaryotic gene (part 1)
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
Transcription of an eukaryotic gene (part 2)
The Eukaryotic Genome and Its Expression - What are the characteristics of the
eukaryotic genome?
?
Protein-coding genes have noncoding
sequences—introns.
The coding sequences are extrons.
Transcripts of introns appear in the premRNA, they are removed from the final
mRNA.
The Eukaryotic Genome and Its Expression - How are eukaryotic gene transcripts
processed?
RNA splicing removes introns and splices
exons together.
Pre-mRNA is bound by small nuclear
ribonucleoprotein particles (snRNPs).
Consensus sequences are short
sequences between exons and introns.
snRNP binds here, and also near the 3′
end of the intron.
The Eukaryotic Genome and Its Expression - How are eukaryotic gene transcripts
processed?
With energy from ATP, proteins are
added to form an RNA-protein complex,
the spliceosome.
The complex cuts pre-mRNA, releases
introns, and splices exons together.
The Eukaryotic Genome and Its Expression - How are eukaryotic gene transcripts
processed?
The spliceosome
The Eukaryotic Genome and Its Expression - How are eukaryotic gene transcripts
processed?
During development, different globin
genes are expressed at different times:
differential gene expression.
γ-globin is in hemoglobin of human
fetus—it binds oxygen more tightly than
adult hemoglobin.
The Eukaryotic Genome and Its Expression - How are eukaryotic gene transcripts
processed?
Differential expression in the globin gene family
The Eukaryotic Genome and Its Expression - How are eukaryotic gene transcripts
processed?
Some gene families have pseudogenes—from
a mutation that results in loss of function.
Pseudogenes may lack a promoter, or
recognition sites for removal of introns.
They are designated by ψ (psi).
Expression of genes must be precisely
regulated during development.
Gene expression can be regulated at several
points in the transcription and translation
processes.
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
?
Potential points for the regulation of
gene expression (part 1)
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Potential points for the regulation of
gene expression (part 2)
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Potential points for the regulation of
gene expression (part 3)
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Local remodeling of chromatin for transcription (part 1)
Proteasome Breaks Down
Proteins
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Local remodeling of chromatin for transcription (part 2)
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Transcription factors, regulators, and activators (part 1)
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Transcription factors, regulators, and activators (part 2)
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Coordinating gene expression (part 1)
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Coordinating gene expression (part 2)
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Transcription from multiple genes for rRNA
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Alternative splicing results in different
mature mRNAs and proteins
The Eukaryotic Genome and Its Expression – How is the eukaryotic gene transcription
regulated?
Proteasome breaks down proteins