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Mbg 2040 > Transposable Elements > Flashcards

Transposable Elements Flashcards

1
Q

What are transposable elements

A

strands of DNA capable of jumping from one location in a chromosome to another

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2
Q

What is significant about transposable elements

A

can constitute a significant fraction of the genome
- major source of mutations
- important in the generation of some human diseases

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3
Q

What are the common characteristics in transposable elements

A
  • create staggered breaks in DNA
  • transposable element attaches to single stranded ends of DNA
  • DNA is replicated at the gaps
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4
Q

What are flanking direct repeats

A

3-12bp long
- generated in the process of transposition
- don’t belong to transposable element

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5
Q

What are terminal inverted repeats

A

9-40bp long
- inverted and complementary
- recognized by enzymes called transposase that catalyzes transposition

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6
Q

What are the 2 classes of transposons

A

class 1: retrotransposons (RNA intermediate)
class 2: DNA-transposons-catalyzed by transposase

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7
Q

What is a class 1 transposon

A

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

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8
Q

What enzyme is required by class 1 transposons

A

reverse transcriptase

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9
Q

What are the two types of class 1 (retrotransposon) transposons

A

retrovirus (or retrovirus-like) elements and retroposons or retrotransposons

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10
Q

Both types of class 1 transposon use ___________ _______________

A

replicative transpositon

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11
Q

What are the two types of class 2 transposons

A

non replicative transposons and replicative transposons

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12
Q

In class 2 of transposons, what are non replicative transposons

A

element is cut out of one site in the chromosome and pasted into another site
- cut and paste

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13
Q

In class 2 of transposons, what are replicative transposons

A

element is replicated with one copy and is inserted into a new site (but the original remains at its original site)
- copy and paste

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14
Q

What mechanisms are in place to control or limit transposition

A
  1. DNA is methylated where transposons are common
  2. Alterations in chromatin structure prevent transcription
  3. control of transposase translation by piwi-interacting RNAs (piRNA) - bind to piwi proteins an inhibit translation of transposase mRNA
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15
Q

Why are transposons considered mutagenic

A

they can insert themselves in DNA

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16
Q

Transposiition is a _______________ mutation

A

spontaneous

17
Q

What (in relation to transposition) causes hemophilia

A

insertion of L1 transposable element into blood clotting factor VIII gene

18
Q

What can be the result of a transposon insertion

A

loss of function mutation - disrupts the coding sequence of a gene
gain of function - activating a nearby gene

19
Q

What is the general end result of transposition

A

duplications, deletions, inversions, and translocations

20
Q

What does transposition entail

A

exchange of DNA sequences and recombination

21
Q

Pairing of direct repeats in transposition leads to what

A

deletion

22
Q

Pairing of inverted repeats in transposition leads to what

A

inversion

23
Q

Transposable elements in bacteria contain two major groups; what are they

A

simple and complex transposable elements

24
Q

What are simple transposable elements in bacteria

A

contain only the information required for movement

25
Q

What are complex transposable elements in bacteria

A

contain extra DNA not related to transposition

26
Q

What are the subcategories of complex transposons in bacteria

A

composite and non composite

27
Q

What 2 genes cause the mosaic colouring in corn

A

Ac-activator gene (transposon) and Ds-dissociation gene (transposon)

28
Q

What are the characteristics of Ac-activator gene

A
  • contains terminal inverted repeats
  • has transposase gene
  • autonomous transposition
29
Q

What are the characteristics of Ds-dissociation gene

A

*similar to Ac
- possess inactivated transposase gene
- requires transposase from Ac to transpose
- non autonomous transposition

30
Q

What are the characteristics of P elements in drosophila

A

about 2900 bp long
- possess inverted repeats
- DNA transposon
- contains both a transposase and a repressor of transposition

31
Q

By containing both a transposase and a repressor of transposition, what phenomenon is created

A

hybrid dysgenesis

32
Q

What is hybrid dysgenesis

A
  • occurs when P elements are introduced into. cell that does not have them in its genome
  • sudden appearance of numerous mutations
  • chromosome aberrations
  • sterility
33
Q

What is the mechanism behind hybrid dysgenesis

A
  • repressor protein is a cytoplasmic protein that inhibits transposition
  • inhibitor is the egg of a female

*if a P+ female is crossed with a P- or P+ male, the inhibitor in the egg will prevent transposition and the fly will be wild type
*If a P- female was crossed with a P+ male, the lack of inhibitor will allow for rapid transposition leading to mutations an sterility (male does not carry repressor in sperm)

34
Q

What are SINES

A

short interspersed elements

35
Q

What are LINES

A

long interspersed elements

36
Q

What is the most common transposable element in the human genome

A

Alu

37
Q

How much of the human genome is SINES

A

11%

38
Q

How much of the human genome is LINES

A

21%

39
Q

How much of spontaneous mutation in drosophila are due to transposition

A

50%

Mbg 2040 (13 decks)

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