Bio 99 Midterm 3 Review Questions With Complete
Solutions
describe one way in which transcription is terminated in
eukaryotes Correct Answers Torpedo Model:
-Termination seq. AAUAAA signals for complex to cleave
mRNA, 3' end further processed.
-Pol II continues transcribing, Xrn2 (exonuclease) chews up
leftover RNA
-When Xrn2 catches up to Pol II, it removes transcript and ends
transcription (similar to Rho-dependent bacteria term.)
Describe the basic similarities and differences between DNA
replication and RNA transcription Correct Answers
Transcription:
-RNA polymerase binds to double stranded DNA
-DNA opens up to expose single strands
-RNA polymerase reads template strand and adds
ribonucleotides (NTPs) to growing RNA chain
-DNA reforms double strand and exits, RNA chain exits
DNA binding activator Correct Answers - binds to other, more
specific sites; not as universal as other transcription factors.
Coactivators are not directly bound to DNA but can still
influence transcription. not needed, but nice to have
Explain the three parts of transcription in bacteria Correct
Answers Initiation
, RNA holoenzyme binds to DNA at promoter consensus
sequence, complex is still closed.
Structure change causes DNA to denature and enter pol. Active
site creating a transcription-competent open complex
(spontaneous, reversible). NTPs are added but structure is
unstable for first 8-10bp and leave the channel- abortive
initiation. Is frequent, and process will begin again until 10bp
are added to stabilize the transcript. SF is initially blocking the
path of the growing RNA and when it is long enough, it will
dislodge the SF which will release from the pol., to where the
RNA strand will exit the promoter and initiation stops - called
promoter clearance.
Elongation
-3 channels in pol.: Dna entry, ntp entry and RNA exit channel
-A pin region of the pol. Keeps 2 DNA strands separated while
in the bubble.
Termination
Rho-Independent Termination sequences (about 15-20
nucleotides at end of RNA - creates hairpin structure) AAA in
template strand creates UUU in rna, which hairpin dislodges
Rho-Dependent Rut site - rho utilization site sequence on RNA
that recruites rho Rho helicase - travels along RNA transcript
When it encounters rut, will hydrolyze ATP to dislodge
transcript and stop translation
general transcription factor Correct Answers (NEEDED) -
common to promoters, assemble at promoter, recruit RNA pol.
Solutions
describe one way in which transcription is terminated in
eukaryotes Correct Answers Torpedo Model:
-Termination seq. AAUAAA signals for complex to cleave
mRNA, 3' end further processed.
-Pol II continues transcribing, Xrn2 (exonuclease) chews up
leftover RNA
-When Xrn2 catches up to Pol II, it removes transcript and ends
transcription (similar to Rho-dependent bacteria term.)
Describe the basic similarities and differences between DNA
replication and RNA transcription Correct Answers
Transcription:
-RNA polymerase binds to double stranded DNA
-DNA opens up to expose single strands
-RNA polymerase reads template strand and adds
ribonucleotides (NTPs) to growing RNA chain
-DNA reforms double strand and exits, RNA chain exits
DNA binding activator Correct Answers - binds to other, more
specific sites; not as universal as other transcription factors.
Coactivators are not directly bound to DNA but can still
influence transcription. not needed, but nice to have
Explain the three parts of transcription in bacteria Correct
Answers Initiation
, RNA holoenzyme binds to DNA at promoter consensus
sequence, complex is still closed.
Structure change causes DNA to denature and enter pol. Active
site creating a transcription-competent open complex
(spontaneous, reversible). NTPs are added but structure is
unstable for first 8-10bp and leave the channel- abortive
initiation. Is frequent, and process will begin again until 10bp
are added to stabilize the transcript. SF is initially blocking the
path of the growing RNA and when it is long enough, it will
dislodge the SF which will release from the pol., to where the
RNA strand will exit the promoter and initiation stops - called
promoter clearance.
Elongation
-3 channels in pol.: Dna entry, ntp entry and RNA exit channel
-A pin region of the pol. Keeps 2 DNA strands separated while
in the bubble.
Termination
Rho-Independent Termination sequences (about 15-20
nucleotides at end of RNA - creates hairpin structure) AAA in
template strand creates UUU in rna, which hairpin dislodges
Rho-Dependent Rut site - rho utilization site sequence on RNA
that recruites rho Rho helicase - travels along RNA transcript
When it encounters rut, will hydrolyze ATP to dislodge
transcript and stop translation
general transcription factor Correct Answers (NEEDED) -
common to promoters, assemble at promoter, recruit RNA pol.
