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Transcription Notes
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DNA must be copied into ____________________________________________________
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____________________
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mRNA complements known as ________________________
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goes from nucleus to the ________________________ in cytoplasm
Only 3 nucleotide “letters” long
Remember RNA has uracil (U) instead of thymine (T)!
Central Dogma of Molecular Biology
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The flow of information in the cell starts at DNA, which ____________________________ to
form more DNA. Information is then _________________________________ into RNA, and
then it is _________________________________ into protein. The proteins do most of the
work in the cell.
Information does not flow _________________________________________________.
Exceptions: Reverse Transcription
Some RNA viruses, called “retroviruses” make a DNA copy of themselves using the enzyme
_____________________________________________________________________.
When does transcription occur?
RNA differs from DNA – Name three differences.
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Transcription – Principal Points
It is catalyzed by the enzyme ________________________________________________
There are similarities and differences in ___________________________________ and
__________________________ mRNA products.
Transcription – 3 stages
STEP 1 - INITIATION
_________________________________ and cofactors bind to DNA and unwind it, creating an initiation
bubble. This is a space that grants RNA polymerase access to a single strand of the DNA molecule.
Prokaryotes - transcription begins with the binding of RNA polymerase to the ___________________ in
DNA.
Eukaryotes - transcription initiation is more complex, a group of proteins called
_______________________factors mediate the binding of RNA polymerase and the initiation of
transcription.
Step 2: _____________________________________________
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One strand of DNA serves as the template for RNA synthesis, but multiple rounds of
transcription may occur so that many copies of a gene may be produced. RNA nucleotides line
up along one strand of DNA, following the base-pairing rules
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The template strand is read 3’ to 5’ - the other strand (5 to 3) is the nontemplate strand.
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Just as in DNA synthesis, nucleotides are added to a 3’ hydroxyl (5’ to 3’)
Step 3: ____________________________________
Results in the release of the newly synthesized mRNA from the elongation complex. Single-stranded
messenger RNA peels away and DNA strands rejoin.
DRAW THE DIAGRAM:
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Transcription in Eukaryotes:
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_________________________________ located exclusively in the nucleolus, catalyzes the
synthesis of 3 of the RNAs found in ribosomes: the 28S, 18S, and 5.8S
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_________________________________, found only in the nucleoplasm, synthesizes mRNAs.
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_________________________________ found only in the nucleoplasm, synthesizes the tRNAs,
5S rRNA, not made by pol II.
Anatomy of the mRNA
The mRNA molecule has 3 main parts in both prokaryotes and eukaryotes.
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5’ untranslated region
____________________________
3’ untranslated region
sequence
What happens to the mRNA –
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Carries instructions from DNA to the rest of the ribosome.
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Tells the ribosome what kind of protein to make
Types of RNA
Genetic information copied from DNA is transferred to 3 types of RNA:
________________________________________ RNA: mRNA
Copy of information in DNA that is brought to the ribosome and translated into protein by tRNA & rRNA.
_________________________________________ RNA: rRNA
Most of the RNA in cells is associated with structures known as ribosomes, the protein factories of the
cells. It is the site of translation where genetic information brought by mRNA is translated into actual
proteins.
_________________________________________ RNA: tRNA
Brings the amino acid to the ribosome that mRNA coded for.
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Prokaryotes versus Eukaryotes – highlighted.
LOCATION
In prokaryotes (bacteria), transcription occurs in the cytoplasm. Translation of the mRNA into proteins
also occurs in the cytoplasm. In eukaryotes, transcription occurs in the cell's nucleus, mRNA then moves
to the cytoplasm for translation.
REQUIREMENTS
DNA in prokaryotes is much more accessible to RNA polymerase than DNA in eukaryotes. Eukaryotic
DNA is wrapped around proteins called histones to form structures called nucleosomes. Eukaryotic DNA
is packed to form chromatin. While RNA polymerase interacts directly with prokaryotic DNA, other
proteins mediate the interaction between RNA polymerase and DNA in eukaryotes.
ADDITIONAL STEPS
mRNA produced as a result of transcription is not modified in prokaryotic cells. Eukaryotic cells modify
mRNA by RNA splicing, 5' end capping, and addition of a polyA tail.
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