lecture 29 Flashcards
mutations pt.2
what is a base analog(antimetabolite) of uracil that can replace thymine in a strand of DNA?
5-bromouracil
what are very unstable and quick reacting molecules that “steal” electrons from nearby stable molecules?
free radicals
what type of environmental factor causes pyrimidine dimers by the formation of covalent linkages localized on cysteine double bonds?
UV light
what does ectopic recombination cause?
chromosome duplication
in terms of evolution, what role do transposons have?
they increase the genome size as they generate some type of mutation when they move
what class of TEs require reverse transcriptase in order to move?
class 1
what class of TEs do NOT require reverse transcriptase in order to move?
class 2
what protein do all DNA transposons(class 2) code for?
transposase
what class of transposons moves through the genome in a “cut and paste” mechanism?
class 2 - DNA transposons
what does TIR stand for?
terminal inverted repeats
what recognizes the TIRs at the ends of the TE?
transposase
what does (F)DR stand for?
(flanking) direct repeats
are (F)DR a part of the TE?
no
what provides a marker for the excision site of the TE once it has been removed?
(F)DRs
what allows retrotransposons to function?
RNA intermediates
do retrotransposons code for transposase?
no
what class of TEs move throughout the genome in a “copy and paste” mechanism?
class 1 - retrotransposons
what do retrotransposons produce?
RNA transcripts
what must happen in order for a retro-transposon to bind?
reverse transcriptase must reverse transcribe the RNA into DNA sequence PRIOR to insertion into target DNA
what are LTRs?
long terminal repeats; located on each end of TE
what are the only active class of transposons in humans?
non-long terminal repeats
what must non-autonomous transposons borrow to move?
reverse transcriptase
what are LINEs?
long interspersed elements, a type of autonomous retrotransposon
what proteins do FUNCTIONAL L1 elements encode?
endonuclease and reverse transcriptase
what does endonuclease do?
cuts DNA
what does reverse transcriptase do?
makes a DNA copy of an RNA transcript
what do NON-functional L1 elements do?
play a role in regulating the efficiency of transcription of the gene in which they reside
what are SINEs?
short interspersed elements, a type of non-autonomous retrotransposon
what are short DNA sequences that represent reverse transcribed RNA molecules originally transcribed by RNA polymerase II?
SINEs
what are the most abundant SINEs?
Alu elements
Alu elements consist of a sequence that contains a site that is recognized by Alu1 which is what?
restriction enzyme
where do Alu elements normally occur?
introns
how does an Alu element end up being translated into the protein product if it begins in an intron?
it can be spliced into mRNA, thereby creating a new exon which is translated
what does alternative splicing allow for in terms of Alu elements?
nature can try out new proteins without losing the original, functioning one
what is the main factor for transposable element function?
where it lands
if a transposable elements lands in a non-coding region, what effect does it have?
not much
if a transposable element lands in a gene, what effect does it have?
mutation, leading to genetic diversity
assume the V gene regulates anthocyanin pigment production in black grapes. when a G retrotransposon is added to the V gene, what is the phenotypic result?
white grapes
what effect does the G retrotransposon have on the V gene in grapes?
it disrupts anythocyanin synthesis, thereby preventing color from being made, resulting in white grapes
assume a white grape undergoes a second mutation wherein the G retrotransposon is removed; however a piece is left behind. what is the phenotypic result and why?
red grapes, because anthocyanin production is partially restored
