Transposable Genetic Elements

Question 1

What are transposons?

Answer 1

transposons are spontaneous mutations (very specific) - segment of DNA moving from one location in chromosome to another

Question 2

How much of gene does chromosome make up?

Answer 2

40-66%

Question 3

What do transposons result in?

Answer 3

chromosome breakage, mutations, antibiotic resistance

Question 4

How do transposons work - Create what kind of breaks (blunt=? sticky=?)? Attach to which end of DNA? DNA is replicated at what?

Answer 4

• create staggered breaks in DNA (blunt cut = transposon and sticky cut = target DNA)
• attach to SS end of DNA
• DNA is replicated at gaps

Question 5

What are transposons made of?

Answer 5

Flanking direct repeats on either side (not part of transposable sequence) and terminal inverted repeats (inverted and complimentary)

Question 6

What enzyme recognizes the termianl inverted repeats?

Answer 6

Transposase

Question 7

2 classes of transposons - retrotransposons - In rna a copy is made from its…? and inserted where?

Answer 7

In RNA a copy of element is made by reverse transcription from its RNA and inserted into a new chromosomal site

Question 8

2 classes of transposons - retrotransposons - what do they require?

Answer 8

Reverse transcriptase (RNA->DNA), retrovirus or retroposons (just cDNA no virus)

Question 9

2 classes of transposons - DNA transposons - Non replicative (blank and blank) and replicative (blank and blank)

Answer 9

short inverted repeats, non replicative (cut and paste) or replicative (copy and paste)

Question 10

What is Control?

Answer 10

mechanisms to control or limit transposition

Question 11

Control - DNA methylated

Answer 11

methylated DNA suppress transcription and prevents production of transposase enzyme

Question 12

Control - alterations in chromatin structure

Answer 12

prevents transcription (ex. heterochormatin)

Question 13

Control - translation

Answer 13

piwi interacting RNA’s - bind to piwi protein and inhibit translation of transposable RNA

Question 14

What is a Mutagenic effect?

Answer 14

insert themselves into DNA - ex. insertion of L1 = hemophilia

Question 15

Mutagenic effect - Insertions (loss-ditrupts what? and gain of functions - acitvates what?)

Answer 15

loss of functions - disrupts coding sequence
gain of functions - activating nearby gene

Question 16

What is Transposition ?

Answer 16

exchange of DNA sequence and recombination

Question 17

What do dna rearrangements lead to? Deletions… direct or inv repeats? Inverisonts.. dir or inv repeats…? Translocation..?

Answer 17

deletions - direct repeats
inversions - inverted repeats
translocation - misalignment on homologous chromosome (1 chrom duplicated and other deleted)

Question 18

Example of transposition in grapes?

Answer 18

Retrotransposons disrupt the gene that transcribes skin colour. No transposon = black grape and with transposon = white

Question 19

Transposons in prok - simple

Answer 19

carry info only for movement (transposase gene and terminal repeats)

Question 20

Transposons in prok - complex

Answer 20

contain extra dna not related along with the transposase gene and terminal repeats

Question 21

Transposons in prok - complex (composite)

Answer 21

sequence is flanked by 2 insertion transposon sequences

Question 22

Transposons in prok - complex (non composite)

Answer 22

terminal inverted repeats and transposon gene, similar to simple

Question 23

Transposons in euk - What two components are involved?

Answer 23

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

Question 24

Transposons in euk - example of ac activator and ds dissociation

Answer 24

Mosaic corn - Ds has transposed out of C allele leaving colour spots

Question 25

Transposons in euk - what do P elements in drosophila contain?

Answer 25

terminal inverted repeats, transposase and repressor transposition which leads to hybrid dysgenesis.

Question 26

Transposons in euk - drosophila - hybrid dysgenesis

Answer 26

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

Question 27

Transposons in euk - humans - SINES

Answer 27

short inverted repeats, alu, 11% of genome, copies of transposable elements containing shortened 5’ end due to termination of reverse transcription

Question 28

Transposons in euk - humans - LINES

Answer 28

long interspersed elements