Transcription and Translation CP 35-36, 49-55 Flashcards
transcription bubble
Region where DNA double helix is temporarily opened up, thus allowing transcription to occur
coding (or antisense)
The strand of DNA that has complementary sequence to mRNA
nontemplate or sense strand
The strand of DNA equivalent in sequence to the messenger RNA (same as plus strand) - complementary to the template strand, sequence is identical to the RNA
What is the general process for how mRNA is made?
1) core enzyme forms a transcription bubble (separates DNA strands)
2) core enzyme add RNA nucleotides in 5’ –> 3’ based off template
3) new RNA anneals to template strand with H bonds between base pairs
How does RNA synthesis start?
starts with a purine (usually A) in CAT by can be CGT
How is DNA unwound during RNA synthesis?
RNA polymerase unwinds the DNA (positive supercoils)
DNA gyrase and topoisomerase I return the DNA back to its normal supercoils afterwards.
Rho-Independent terminator (in bacteria)
region of DNA with two inverted repeats separated by ~6 bases followed by a stretch of A’s - As the A’s become U’s the DNA/RNA hybrid molecule becomes unstable (2 H bonds) and falls off the template strand.
Transcriptional terminator that does not need Rho protein
Rho-dependent terminators (in bacteria)
Transcriptional terminator that depends on Rho protein
Rho binds to cytosine heavy site and attaches to the RNA moving along until it catches up to the RNA polymerase at the hairpin structure. The Rho then unwinds the DNA/RNA helix and releases the RNA.
Rho protein
protein factor needed for successful termination at certain transcriptional terminators
How is bacterial mRNA translation different than eukaryotic mRNA translation?
bacterial mRNA is translated without any processing, can undergo coupled transcription/translation
eukaryotic mRNA cap
Structure at the 5′ end of eukaryotic mRNA consisting of a methylated guanosine attached in reverse orientation
a methylated (on position seven of G) GTP
what are the three parts of eukaryotic mRNA processing?
1) cap
2) poly(A)-tail
3) intron removal
poly(A) tail
A stretch of multiple adenosine residues found at the 3′ end of mRNA
what three sequences regulate the addition of the poly(A) tail?
1) recognition sequence for the polyadenylation complex (AAUAAA)
2) the cute site cleavage for the binding factor
3) the recognition sequence for polyadenylation binding protein
polyadenylation complex (AAUAAA)
Protein complex that adds the poly(A) tail to eukaryotic mRNA
What is the general process in which the poly(A) tail is added?
1) polyadenylation complex binds to AAUAAA
2) endonuclease cuts mRNA
3) poly(A) polymerase adds 100-200 adenine nucleotides
4) poly(A) binding protein binds to poly(A) tail and cap structure
makes mRNA more stable and prevents degredation
introns
Segment of a gene that does not code for protein but is transcribed and forms part of the primary transcript
streches of intervening sequence
exons
Segment of a gene that codes for protein and that is still present in the messenger RNA after processing is complete - regions that will ultimately code for a protein
primary transcript
The original RNA molecule obtained by transcription from a DNA template, before any processing or modification has occurred - is capped and tailed before introns can be removed
splicing factors
Proteins that remove intervening sequences and rejoin the ends of a molecule; usually refers to removal of introns from RNA
recognize the exon and intron borders, cut DNA, and splice exons together
how do the three modifications occur in terms of time?
capping occurs first - poly(A) tail addition and splicing occur simultaneously
when does transcription end?
when the poly(A) tail addition releases the mRNA from RNA polymerase. the mRNA then moves from the nucleus to the endoplasmic reticulum so it can be translated by the ribosomes.
Where is mRNA made in the eukaryotes?
In the nucleus
Where does translation occur in eukaryotes?
On the ribosomes in the cytoplasm