Download 4. Transcription in Detail

Transcription in Detail
Three main phases: 1. ______________2. ________________3. ______________
The Three Phases: Initiation
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Transcription commences when ____________________ binds to the DNA molecule
It binds ______________________of the gene to be transcribed
Upstream region is known as the _________________________
Promotor has a string of ________________________
The 2 H bonds between A-T are ___________________________________
Elongation
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mRNA is built in the __________________________direction
DNA strand used is called the ________________________________
Strand not used is called the _________________________
Termination
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RNA polymerase recognizes the end of the gene when it comes across a
_______________________________ and __________________ disassociates
Posttranscriptional Modifications
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Occurs in _______________________________ only
Called ________________________________________
5’ is added to the start of the primary transcript, it consists of __________________
The cap ______________ mRNA from ____________ by nucleases and phosphatases
200 _______________ ribonucleotides are added to the 3’ end by enzyme poly-Apolymerase called _______________________
Introns
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Introns are removed: _____________________________________
If introns are not removed protein will not _____________________________
Introns are removed by _____________________________who cut out the introns and join
the remaining _______________________________________________
mRNA Transcript
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Therefore the primary transcript is ______________, tailed and ___________ excised – now
it is called___________________________________.
Unlike DNA there is no_____________________________, but if an error is made during
transcription the protein is susceptible to degradation once it is synthesized.
The correct copies made adequate amounts of the protein.
Translation in Detail
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mRNA leaves the _______________and enters the ___________________
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________________________bind to the mRNA recognizing the 5’ cap in eukaroytes
This is _______________________of translation.
Ribosome
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The ribosome consists of_______________________:
A large subunit of ______ and a small subunit of __________
The S refers to the rate at which various components ___________when centrifuged
The two subunits ________ to the mRNA, _____________ the mRNA between them.
Reading Frame
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The ribosome moves along the mRNA in the ___________________direction.
The ribosome reads the mRNA coding sequence, in _____________of nucleotides
The phase of reading the mRNA is calling the ______________________
Positioning is ____________________, because reading frame can _________depending on
the base pair from which the ribosome________________.
Transfer RNA (tRNA)
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The correct amino acids must be _________________to the polypeptide-building site.
_______________________delivers the amino acids
It is a small single-stranded nucleic acid whose structure resembles a _____________
At one _____ of tRNA a sequence of three bases (the ______________) recognizes the
codon of the mRNA
The ___________________ arm carries the corresponding__________________.
Wobble Hypothesis
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tRNa can bind to mRNA even if its _________________in its anticodon is different - this
provides _____________________eg. AUA still binds to UAC
_____________________ tRNA carries amino acid
_____________________ tRNA lacks an amino acid
_____________ that adds the appropriate amino acid is aminoacyl-tRNA synthetases (20
different enzymes)
Acceptor Sites
Ribosome has _________________________for tRNA:
1. ____ acceptor site - where tRNA brings an ________________
2. ____ peptide site - where _______________________ are formed
The first tRNA that is brought into the P site carries _________________ because the start code
is ____________.
The second tRNA enters the _________ site
A ____________________ bond forms between methionine and alanine.
The ribosome ________________________the mRNA and adds another amino acid
Process is repeated until __________________________________is reached
Complex is dismantled and ________________________________is released.
Stop Codons
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There are three stop codons ___________________________________
A protein known as _____________________________aids in the release of the polypeptide
chain
Review
1. When does transcription commence?
2. What is the promotor?
3. What is the DNA strand that is used called?
4. What are two post transcriptional modifications made to primary transcript of mRNA?
5. How is the mRNA held by the ribosome?
6. Why is the reading frame important?
7. What is the name of the 3 bases that hold the amino acid to the tRNA?
8. What is the start codon on the mRNA?
9. What happens at the P site?
10. What is a stop codon?