Download Eukaryotic Transcription

Eukaryotic Transcription
• Eukaryotic Cells – cells with a
nucleus and many organelles
• Organisms with nucleated cells
belong to the largest classification
group, Domain Eukaryota
• Four Kingdoms of Organisms which
are eukaryotic are animal, plants,
protists and fungi.
Basic Principles of Transcription
• Transcription is the synthesis of RNA under the
direction of DNA
• Transcription produces messenger RNA (mRNA)
• In a eukaryotic cell, the nuclear envelope
separates transcription from translation
• Eukaryotic RNA transcripts are modified through
RNA processing to yield finished mRNA
• mRNA is a copy of the genetic code of organism.
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Where is the TATAA box located?
In which step does the initiation complex form?
Transcription factors are associated with which
structures in the diagram?
Where would the codon AUG be located?
Where are the genes to make a polypeptide
located?
Where is the termination signal located?
What unwinds or melts the DNA to allow for
transcription
What is another name for RNA transcript?
Protein Synthesis: Eukaryotic Transcription
Concept 17.3: Eukaryotic cells modify
RNA after transcription
• Enzymes in the eukaryotic nucleus modify premRNA before the genetic messages are
dispatched to the cytoplasm
• During RNA processing, both ends of the
primary transcript are usually altered
• Also, usually some interior parts of the molecule
are cut out, and the other parts spliced together
• Exon – coding region and Intron –noncoding
region
Make a table like the one below in your notebook. As
you watch the video, complete it with information.
Prokaryotic vs Eukaryotic Transcription
Characteristic
Nucleus present
Uses a specific type of RNA
polymerase
Have Ribosomes
Location of Transcription
DNA contains exons
DNA contains introns
Modifies mRNA
Location Translation
Prokaryotic Cell
Eukaryotic Cell
LE 17-3-5
DNA
TRANSCRIPTION
mRNA
Ribosome
TRANSLATION
Polypeptide
Prokaryotic cell
Nuclear
envelope
DNA
TRANSCRIPTION
Pre-mRNA
RNA PROCESSING
mRNA
Ribosome
TRANSLATION
Polypeptide
Eukaryotic cell
Prokayotic versus Eukaryotic Proteins Synthesis
• Smaller cell size
• No nucleus – nucleoid
region for DNA
• Ribosome only organelle
• Smaller size
chromosome
• Circular chromosome
• Chromosome contains
only coding regions for
proteins
• Larger cell size
• Nucleus contains DNA
and a nucleolus for RNA
• Ribosome and other
organelles
• Larger size chromosome
• Linear chromosome
• Chromosome contains
coding and noncoding
regions for proteins
Splicing exons
5 Exon Intron
Pre-mRNA
5
Exon
Intron
Exon
3
Cap
Poly-A tail
1
30
31
Coding
segment
5
104
105
146
Introns cut out and
exons spliced together
Poly-A tail
Cap
5 UTR
1
146
3 UTR
Alteration of mRNA Ends in Eukaryotic Cells
• Each end of a pre-mRNA molecule is modified in
a particular way:
– The 5 end receives a modified nucleotide cap
– The 3 end gets a poly-A tail
• These modifications share several functions:
– They seem to facilitate the export of mRNA
– They protect mRNA from hydrolytic enzymes
– They help ribosomes attach to the 5’ end
LE 17-12
Gene
DNA
Exon 1
Intron
Exon 2
Transcription
RNA processing
Translation
Exon 2
Polypeptide
Intron
Exon 3
LE 17-11
RNA transcript (pre-mRNA)
5
Exon 1
Intron
Exon 2
Protein
Other proteins
snRNA
snRNPs
Spliceosome
5
Spliceosome
components
Cut-out
intron
mRNA
5
Exon 1
Exon 2
• In some cases, RNA splicing is carried out by
spliceosomes
• Spliceosomes consist of a variety of proteins and
several small nuclear ribonucleoproteins
(snRNPs) that recognize the splice sites
• RNA splicing can lead to genetic diversity
Helpful Transcription Animation Links
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Stages of Transcription: Components
Transcription Factors
RNA Splicing and Spliceosome
RNA Splicing