Transposable elements

Question 1

What are transposable elements (TE) ?

Answer 1

DNA segment (50bp-10kb) that moves to other sites in the genome

Question 2

True or false : Transposable elements can cause mutations

Answer 2

true

Question 3

True or false : transposable elements can only move through the same chromosome

Answer 3

False

Question 4

Are transposable elements found in prokaryotes or eukaryotes ?

Answer 4

both

Question 5

What is the function of transposable elements ?

Answer 5

Its function is uncertain

Question 6

True or false : transposable elements consitute 30% of the human genome

Answer 6

False, 50%

Question 7

What’s a DNA transposon?

Answer 7

Mobile genetic elements that are excised from one site in the genome and inserted directly into another, often causing mutations
(No RNA intermediate)

Question 8

To which type of transposable element does the #CutAndPaste refer to ?

Answer 8

DNA transposons

Question 9

Name the 2 elements that are required for DNA transposons

Answer 9

• Transposase : ORF (open reading frame) that codes for an enzyme
• Inverted terminal repeats (ITRs) : at each end of the ORF + they get recognized by the transposase

Question 10

Whats an Open Reading Frame (ORF) ?

Answer 10

Nucleotide sequence organized as triplets that encodes the amino acid sequence of a polypeptide, including an initation codon and a termination codon

Question 11

What are direct repeats (DRs)?

Answer 11

Short repeated sequences generated during insertion

Question 12

DNA transposons compose __% of the human genome

Answer 12

3

Question 13

Name the steps transposons go through

Answer 13

1. Cleavage of the transposon out of the chromosomal DNA by the transposase
2. The transposase cuts a new target in the genome (at an identical sequence)
3. The transposase inserts the transposon
4. A DNA polymerase synthesizes the complementary sequence
5. A ligase attaches the new transposon sequence to the filled overhang

Question 14

Give an example of how we can modify genes through transposons

Answer 14

• Adding an antibiotic resistance gene to a DNA sequence
• Generates DNA with that feature (resistance)
• Then we can use that transposon to give that feature to another organism (by giving the transposon to the other organism)

Question 15

What are retrotransposons ?

Answer 15

Mobile genetic elements that are copied by means of an RNA intermediate and inserted at other chromosomal sites, often causing mutations

Question 16

To what type of transposable elements does #CopyPaste refer to ?

Answer 16

Retrotransposon

Question 17

What are the 2 types of retrotransposons ?

Answer 17

• Long-terminal-repeat (LTR) : includes promoter and polyadenylation signal
• Non-LTR : promoter and polyadenylation signal are in the 5’-UTR and 3’-UTR (respectively)

Question 18

Retrotransposons compose __% of the human genome

Answer 18

42

Question 19

What is an Autonomous TE ?

Answer 19

Transposable element that contains all of the information necessary for transposition or retrotransposition to occur

Question 20

What is a non-autonomous TE ?

Answer 20

Transposable element that lacks the gene that encodes the transposase or reverse transcriptase necessary for transposition to occur

Question 21

Name the steps to Copy-Paste mechanism

Answer 21

1. Transcription and translation (by cellular RNApol)
2. Reverse transcriptase converts the retrotransposon RNAs back to DNA
3. Integrase inserts the retrotransposon DNA back into the genome

Question 22

True or false : mutliple RNA copies can be converted back to DNA with the Copy-Paste mechanism

Answer 22

True

Question 23

Can mutations through transposable elements be reversible ?

Answer 23

Yes (if transposon moves again)

Question 24

what’s a SINE?

Answer 24

Short interspersed elements :
- One of the major types of TE in humans
- Non-LTR
- Non-autonomous

Question 25

What's a LINE ?

Answer 25

long interspersed elements: - one of the major types of TE in humans - Non-LTR - Autonomous

Question 26

Together, SINEs and LINEs compose __% of the human genome

Answer 26

34

Question 27

Describe the Alu family of repetitive sequences

Answer 27

- SINE - 200bp long - 10% of the human genome - Derived from the 7SL RNA gene - Has been copied by retrotransposition many times (1 million copies in the human genome) - 7SL synthesizes SRP, which guides the protein vesicule through the endoplasmic reticulum

Question 28

Describe thhe LINE1 gene

Answer 28

- LINE - 6,5kb long - 17% of the human genome - 500 000 copies

Question 29

What happens if a TE inserts itself in a coding region ?

Answer 29

Frameshift or Premature termination of translation

Question 30

What happens if a TE that contains a polyadenylation signal inserts itself into a gene's intron ?

Answer 30

- Terminates transcription - Aberrant splicing of the mRNA

Question 31

What happens if a TE inserts itself in a gene's transcription regulatory region (promoter or enhancer sequence) ?

Answer 31

- Disrupt the gene's normal regulation - Cause change in the expression level

Question 32

What happens if there are 2 or more TEs in a genome ?

Answer 32

Potential for recombination between the transposons : duplications, deletions, inversions, chromosome translocations...

Question 33

__% of detectable human mutations may be due to TE insertions

Answer 33

0.2

Question 34

True or false : TEs contribute to evolution

Answer 34

True