All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #21 : Dna
What term best describes when RNA polymerase binds promoters and synthesizes and releases short mRNA transcripts in cycles before the RNA holoenzyme leaves the promoter?
Promoter clearance
Cyclic initiation
DNA scrunching
Abortive initiation
Repressive transcription
Abortive initiation
The correct answer is abortive initiation. This is a normal transcription event is found in both prokaryotes and eukaryotes and occurs prior to promoter clearance, or the event when RNA polymerase escapes the promoter and begins elongation of synthesized transcripts. Abortive initiation is thought to occur when the RNA polymerase complex is not stable enough on the DNA. DNA scrunching describes the mechanism by which RNA polymerase transcribes, rather than RNA polymerase moving along DNA, it actually pulls DNA into the complex and unwinds it.
Example Question #22 : Dna Replication And Repair
Branched nucleic acid structures containing 4 double-stranded arms that are intermediates in genetic recombination and DNA repair are best known as?
Holliday junction
None of these
Spliceosome
Pyrimidine dimers
Replication fork
Holliday junction
The correct answer is Holliday junction. These intermediates in genetic recombination have symmetrical sequence and are mobile to preserve specific base pairing at recombination and damage loci. Repair enzymes recognize and subsequently localize to this DNA structure to facilitate locus specific enzymatic activity.