Exam II Flashcards
What kind of viruses and gene elements encode reverse transcriptase?
Retroviruses, pararetroviruses, class I transposable elements, and LINES
T/F: SINES encode their own reverse transcriptase
False; they muse use RT from other transposable elements
What distinguishes class I transposable elements from class II TE’s
Class I TE’s use RT while Class II TE’s move through a ‘cut and paste’ mechanism
T/F: Reverse transcriptase has proofreading activity
False: this accounts for high genetic variability in viruses
What two characteristics distinguish RT from other polymerases?
1) RT can use both primed ssRNA and primed ssDNA as template
2) Has intrinsic Rnase H activity - degrades the RNA in strand in the RNA:DNA hybrid
Describe RT structure
heterodimer of an beta-subunit with the polymerase and RNAse H activity and alpha-subunit that helps to load p66 onto the template primer
What is the function of telomerase?
Replication of the ends of the chromosomes
What is the function of telomeres?
Protect genomic information at the ends of chromosomes and provide a way to distinguish dsDNA breaks from chromosome ends
What proteins are required for a pre-RC in prok.?
DnaA - Origin recognition protein
DnaB - Helicase
DnaC - Helicase loader
SSB
What triggers nucleosome disruption ahead of the replication fork?
FACT and CMG helicase
What is the function of Dmnt1?
Maintenance of 5mC - recognizes hemimethylated cytosines
What is the function of Dmnt3?
De novo methylation of cytosines
How is Dmnt3 targeted to unmethylated DNA?
ADD domain recognizes H3K4me0 and does not bind H3K4me3
What mechanism exists to silence transposons in germ cells when DNA methlyation is erased?
PIWI interacting RNA (piRNA)
Where does bidirectional replication begin in Eukaryotes?
The DNA Unwinding Element (DUE)
Where do origin recognition proteins bind in euk.?
Origin Recognition Element (ORE)
What is the function of origin recognition proteins?
Unwind the helix at the DUE either directly or indirectly
T/F: DnaA binds OriC in a sequence specific manner
True; recognizes a consensus sequence in the ORE
What prevents re-replication in prok,?
1) Hda (bound to beta-clamp) triggers ATP hydrolysis of DnaA. DnaA-ATP –> DnA-ADP
2) SequestrinA binds hemimethylated adenosine preventing interaction of DnaA
When are the core histone proteins synthesized?
During S-phase
When do pre-RC form in euk.?
During G1
What prevents re-replication in euk.?
1) Cdc6 phosphorylation by S-CDK during S-phase
2) ORC phosphorylation by S-CDK during S-phase
3) Geminin meditated inhibition of Cdt1 during S-phase
What does ORC need to recruit Cdc6 and Cdt1 to the origin?
ATP
What H3 marks are associated with euchromatin?
H3K4me3 and H3K9Ac
What H3 marks are associated with heterochromatin?
H3K9me and H3K27me
