MBG Part Two: Lecture 14 Flashcards
What is a major difference between HBR and NHEJ repair mechanisms?
HDR requires enzymes to direct strand invasion, while NHEJ does not
In nucleotide excision repair what happens?
The DNA is first separated, followed by removal by helicase, and sealed by ligase
Ionizing radiation leads to dimerization of pyrimidine bases. Which mechanisms can the cell use to repair this mutation?
Direct Repair, Nucleotide Excision Repair
If depurination is detected, what repair mechanism would the cell use to fix it?
Base Excision Repair
What are Transporable Elements?
Segments of DNA capable of moving from one location in a chromosome to another
What is the LINE transposon estimated to undergo?
Every 1 transposon in every 100 births
What do transposable elements lead to?
Chromosome breakage and insert in new locations
What can bacterial transposons carry?
Antibiotic Resistance Genes
What type of breaks do transposable elements make?
A staggered break
Where do transposable elements ts attach to?
Single Stranded ends of DNA
Where is DNA replicated?
At the gaps
What are Flanking Direct Repeats?
3 -12bp long and generated in the process of transposition but do not belong to the transposable element
What is the transposase enzyme?
Makes the staggered break in the DNA and catalyzes the transposition
What are Terminal Inverted Repeats?
9 - 40 bp long, inverted and complimentary and found at the ends within many transposable elements
What are Class I: Retrotransposons?
RNA is transcribed from the transposable element (DNA)
The DNA copt us made from RNA by reverse transcription and inserted into a new chromosome site.
What does Retrotransposons require?
A reverse transcriptase - reverse flow of genetic material from RNA to DNA
What does Class II: DNA transposons-catalyzed by transposase consist of?
- Non Replicative Transposons
- Replicative Transposons
What are Non-Replicative Transposons?
Element is physically cut out of one site in a chromosome and pasted into new site (cut and paste), the number of transposable elements is preserved (no replication)
What are Replicative Transposons?
Element is replicated with one copy and inserted at a new site (copy and paste leading to the number of transposable elements increasing)
What does Class II DNA Transposition not require?
An RNA intermediate
What types of transposons are in Eukaryotes?
Retrotransposons and DNA transposons
What types of transposons are in Prokaryotes?
DNA transposons
What mechanisms are in place to control or limit transposition?
DNA methylation
- Suppresses transcription
- Prevents the production of transposase enzyme
Alterations in Chromatin Structure to prevent transcription
Control of Transposase Translation by piRNAs
What type of mutation is transposition?
A spontaneous mutation causing insertion (loss of function or gain of function)
What does Transposition Lead to?
Duplications, Deletions, Insertions and Translocations
How is Transposable Elements shown within a grape mutation?
Black Pigments in grapes (controlled by TF VVmybA!)
A retrotransposon insertion Gret1 disrupted gene resulting in white grapes
Red grapes came from a partial removal of retrotransposon which resulted in an intermediate
How can deletion occur?
Pairing of direct repeats
How can inversion occur?
Pairing of Inverted Repeats
What can a misalignment of transposable elements on sister chromatids cause?
- Insertion or Deletion
- Translocation
- Duplication in other sister chromatid
