Transposable elements - Lecture 1

Question 1

What are cut-and-paste transposons, what enzyme do they use, and where are they found?

Answer 1

element is physically cut out of one site in a chromosome and placed to a new site; transposase; prokaryotes and eukaryotes

Question 2

Describe the structure of insertion sequences.

Answer 2

• contains only genes that are involved in transposition
• transposase encoding gene is located in the middle with terminal inverted repeats on either sides and target site duplications on both sides of terminal inverted sequences

Question 3

What are terminal inverted repeats?

Answer 3

identicalish inverted sequences at both ends of element (go in opposite directions, ex: one goes 5’ to 3’ while other goes 3’ to 5’)

Question 4

What are target site duplications?

Answer 4

repeated sequences found on both ends of elements (go same direction)

Question 5

What is the mechanism of IS element insertion?

Answer 5

• staggered cuts are made in the target DNA
• transposable element insert’s itself into DNA
• the staggered cuts leave ssDNA which is filled by DNA synthesis creating direct repeats

Question 6

What are multiple IS elements?

Answer 6

When a certain IS element is found on both a plasmid and a chromosome and crossing over occurs so the IS element moves between DNA sequences

Question 7

What are composite transposons?

Answer 7

a type of cut-and-paste transposons where two IS elements are located near each other and capture a DNA sequence that will move with the transposons when they do

Question 8

What are replicative transposons, what enzyme do they use, and where are they found?

Answer 8

when the element is replicated and one copy is inserted at a new site while the original copy stays put; transposase; only in prokaryotes

Question 9

What makes the structure of replicative transposons different than IS elements?

Answer 9

larger and contains genes (tnpR, beta-lactamase, Res site) that are not involved in transposition (often caries anti-biotic resistant genes

Question 10

Describe the mechanism of replicative transposons.

Answer 10

Consists of two plasmids, one with the tn3 and one without, that combine to make a big chromosome. The Tn3 then replicates so the chromosome has 2 Tn3 and then it breaks off into two chromosomes each with a copy of Tn3

Question 11

What transposons are only found in eukaryotes?

Answer 11

retrotransposons