Transcription Flashcards
What are the basic principles of transcription and translation?
- RNA is the bridge between genes and the proteins for which they code
- Transcription is the synthesis of RNA index the direction of DNA
- Transcription produces mRNA
- Translation is the synthesis of a polypeptide, using information in the mRNA
- ribosomes are the sites of translation
How can transcription initiation differentiate between prokaryotes and eukaryotes?
In prokaryotes, translation of mRNA can begin before transcription has finished
- In a eukaryotic cell, the nuclear envelope separates transcription from translation
- eukaryotic RNA transcripts are modified through RNA processing to yield finished mRNA
What is a primary transcription?
A primary transcription is the initial RNA transcript from any gene prior to processing
What happens to the Thymines if the RNA transcript? Which strand is complementary to the RNA transcript?
- The sense strand of DNA has the same sequence as the mRNA; however in mRNA all of the T’s are replaced with U’s
- The antisense strand of DNA is complementary to mRNA and is used as the template for mRNA synthesis
What are the 3 regions of a prokaryotic gene?
- Promoter
- RNA coding sequence
- Terminators
What is the promoter of the prokaryotic region?
Promoter: located upstream of the RNA coding sequence, and ensures the proper location of transcription initiation
What is the RNA coding sequence of a prokaryotic gene?
The DNA sequence that is transcribed into RNA
What is the terminator of a prokaryotic gene?
Terminator: a sequence downstream of the RNA coding sequence and specifies where transcription will stop
What is the first step in gene expression?
transcription
What catalyzed RNA synthesis ?
RNA synthesis is catalyzed by RNA polymerase, which pries the DNA strands apart and hooks together the RNA nucleotides
The RNA is complementary to the DNA template strand
What are the 3 stages of transcription?
- initiation.
- elongation;
- termination
Describe the initiation of transcription
- during transcription, only one strand of DNA is required as a template
- there is evidence that genes can be transcribed from any strand.
- The strand serving as the template for transcription is called the antisense strand and the other strand is called the coding strand or sense strand (same sequences as the RNA)
Where is the prokaryote promoter sequence?
The prokaryotic promoter sequences are generally found at -35 and -10 bp from the transcription start site
- 35 consensus sequence: 5’ -TTGACA-3’
- 10 consensus sequence : 5’ TATAAT-3’ (also called the pribnow box)
Variation with these sequences results in variation in the binding ability of RNA polymerase and can affect the rate of transcription
How will the coding strand be different from the RNA transcript?
Note that the coding strand and the RNA transcript will have the same bases from 5’ to 3’
-With the consideration that uracil is substituted for thymine
How can transcription be terminated?
Termination occurs at the termination site of the DNA
-RNA polymerase and the new mRNA transcript is released
What is the function of RNA polymerase?
RNA polymerase catalyzes the synthesis of an RNA molecule in 5’ to 3’ direction along the 3’ to 5’ template strand of the DNA
Ribonucleoside triphosphate are the RNA precursor molecules used for RNA synthesis
Compare RNA and DNA synthesis
RNA synthesis- RNA polymerase, NTPs precursor, no primer needed, uracil pairs with adenine
DNA synthesis- DNA polymerase, dNTP precursor, primer required for initiation, thymine pairs with adenine
What are the four different types of RNA molecules and what their functions are?
- mRNA- encodes the amino acid sequence of a polypeptide. mRNAs are the transcripts of protein coding genes
- tRNA- brings amino acids to the ribosome during the translation process.
- rRNA- combines with ribosomal proteins to form the ribosome. mRNA is translated into protein at the ribosome
- snRNA- combines with certain proteins and is involved in RNA processing (example mRNA splicing) in eukaryotes
In bacteria, there is only a single….
RNA polymerase
Differentiate the three different RNA polymerases in eukaryotes
- RNA polymerase I: 5.8s, 18s and 28s rRNA genes
- RNA polymerase II: all protein-coding genes (mRNA) and some snRNAs
- RNA polymerase III: tRNA genes and some snRNAs
What is bacterial RNA polymerase?
RNA polymerase core enzyme is a multi-subunit complex that synthesizes RNA using DNA as a template
RNA polymerase moves stepwise along the DNA
RNA polymerase plus sigma factor (holoenzyme) adheres weakly to bacterial DNA and slides along DNA until it reaches a promoter region where it binds tightly and opens up the double helix to expose a short stretch of DNA
Where does the RNA polymerase plus sigma factor bind?
To the -10 to -35 regions
Briefly describe the method of transcription
- RNA polymerase plus sigma factor binds to the -35 to -10 regions
- DNA molecule is unwound by approximately 17 bp in the -10 region
- Transcription begins
- Once RNA polymerase synthesizes about 10 nucleotides, interactions of sigma factor with the promoter begins to weaken and breaks
- The sigma factor is released and elongation of the RNA transcript continues
- Elongation continues until the termination signal is encountered. The termination signal is “self complementary”. The tail of the mRNA forms a short double-helix hairpin loop
- The RNA hairpin loop causes physical stress on the enzyme complex which destabilizes the polymerase hold on the RNA. RNA is released. Double helix reforms
Describe eukaryotic promoters
Consist of a collection of conserved short sequence elements located near the transcription start site
