Transposable Genetic Elements Flashcards
What are transposons?
transposons are spontaneous mutations (very specific) - segment of DNA moving from one location in chromosome to another
How much of gene does chromosome make up?
40-66%
What do transposons result in?
chromosome breakage, mutations, antibiotic resistance
How do transposons work - Create what kind of breaks (blunt=? sticky=?)? Attach to which end of DNA? DNA is replicated at what?
- create staggered breaks in DNA (blunt cut = transposon and sticky cut = target DNA)
- attach to SS end of DNA
- DNA is replicated at gaps
What are transposons made of?
Flanking direct repeats on either side (not part of transposable sequence) and terminal inverted repeats (inverted and complimentary)
What enzyme recognizes the termianl inverted repeats?
Transposase
2 classes of transposons - retrotransposons - In rna a copy is made from its…? and inserted where?
In RNA a copy of element is made by reverse transcription from its RNA and inserted into a new chromosomal site
2 classes of transposons - retrotransposons - what do they require?
Reverse transcriptase (RNA->DNA), retrovirus or retroposons (just cDNA no virus)
2 classes of transposons - DNA transposons - Non replicative (blank and blank) and replicative (blank and blank)
short inverted repeats, non replicative (cut and paste) or replicative (copy and paste)
What is Control?
mechanisms to control or limit transposition
Control - DNA methylated
methylated DNA suppress transcription and prevents production of transposase enzyme
Control - alterations in chromatin structure
prevents transcription (ex. heterochormatin)
Control - translation
piwi interacting RNA’s - bind to piwi protein and inhibit translation of transposable RNA
What is a Mutagenic effect?
insert themselves into DNA - ex. insertion of L1 = hemophilia
Mutagenic effect - Insertions (loss-ditrupts what? and gain of functions - acitvates what?)
loss of functions - disrupts coding sequence
gain of functions - activating nearby gene
What is Transposition ?
exchange of DNA sequence and recombination
What do dna rearrangements lead to? Deletions… direct or inv repeats? Inverisonts.. dir or inv repeats…? Translocation..?
deletions - direct repeats
inversions - inverted repeats
translocation - misalignment on homologous chromosome (1 chrom duplicated and other deleted)
Example of transposition in grapes?
Retrotransposons disrupt the gene that transcribes skin colour. No transposon = black grape and with transposon = white
Transposons in prok - simple
carry info only for movement (transposase gene and terminal repeats)
Transposons in prok - complex
contain extra dna not related along with the transposase gene and terminal repeats
Transposons in prok - complex (composite)
sequence is flanked by 2 insertion transposon sequences
Transposons in prok - complex (non composite)
terminal inverted repeats and transposon gene, similar to simple
Transposons in euk - What two components are involved?
Ac-activator: contains terminal inverted repeats and transposase gene. Results in autonomous transposition
Ds-dissociation: inactivated transposase gene, requires transposase from Ac to transpose. Results in non autonomous
Transposons in euk - example of ac activator and ds dissociation
Mosaic corn - Ds has transposed out of C allele leaving colour spots
Transposons in euk - what do P elements in drosophila contain?
terminal inverted repeats, transposase and repressor transposition which leads to hybrid dysgenesis.
Transposons in euk - drosophila - hybrid dysgenesis
if p+ female mates with p- males the inhibitor in the egg will prevent transcription = wild type fly
if p- female and p+ male no inhibitor from egg leads to rapid transcription and mutation/sterility bcs sperm has no repressor/cytoplasm
Transposons in euk - humans - SINES
short inverted repeats, alu, 11% of genome, copies of transposable elements containing shortened 5’ end due to termination of reverse transcription
Transposons in euk - humans - LINES
long interspersed elements
