Ch. 15 Transposable Elements & Retroviruses (Exam 2)

Question 1

What are transposons?

Answer 1

Mobile elements capable of transporting themselves to other locations in the genome

Question 2

What are Class II (DNA-type) elements?

Answer 2

Transposons able to manipulate DNA to spread themselves throughout the genome

Question 3

What are Class I (retroelement) elements?

Answer 3

Transposons able to move only bc of their ability to make DNA out of their RNA and integrate that DNA into new sites in the genome

Question 4

You’ll find transposons that use DNA to mobilize in both prokaryotes and eukaryotes, but transposons that use an RNA intermediate are predominantly found in…

Answer 4

Eukaryotes

Question 5

How do transposable elements cause variation in the genome?

Answer 5

They promote genome rearrangement either directly or indirectly

Question 6

Transposons serve as substrates for cellular recombination systems by functioning as…

Answer 6

Portable regions of homology

Question 7

Why is it bad to have two copies of a transposon at different locations?

Answer 7

Deletions, insertions, inversions, or translocations can occur, which would be abnormal

Question 8

In 1950, Barbara McClintock discovered the first transposable elements in corn. What were they?

Answer 8

Ac/Ds elements

Question 9

What are insertion sequence (IS) elements?

Answer 9

The simplest bacterial transposons

Question 10

What are composite elements?

Answer 10

IS elements bordering/flanking a DNA segment with one or more genes

Question 11

How are Tn3-type transposons unique?

Answer 11

They have their own transposase and do not require IS elements

Question 12

What are transposable phages?

Answer 12

Bacterial viruses which transpose as part of their normal infection cycle

Question 13

What is transposase?

Answer 13

Enzyme that catalyzes transposition

Question 14

What is special about the IS elements in composite transposons?

Answer 14

They have inverted terminal repeats and generate direct repeats of flanking DNA at the target site

Question 15

What is a common mechanism that transposons use to introduce themselves in DNA?

Answer 15

Nicks are placed contralaterally (up-left, down-right) at the target site of a DNA strand, and the transposon is placed between the target site

Question 16

What is replicative transposition?

Answer 16

Transposon copied as part of its movement such that a copy is made each time it enters a new site

Question 17

While transposase works on the ends of the original transposon, resolvase words on the…

Answer 17

Duplicated copies

Question 18

What is nonreplicative transposition?

Answer 18

Transposon moves from one site to another without being copied

Question 19

The mechanism behind nonreplicative transposition is often referred to as…

Answer 19

Cut-and-paste

Question 20

What effect does nonreplicative transposition have on the donor strand?

Answer 20

The donor strand now has a DSB that must be repaired

Question 21

What is cointegration?

Answer 21

Fusion of donor and recipient replicon that creates two copies of a transposon, which results in homologous recombination of the copies into 2 different replicons

Question 22

Mu transposition is a mechanism of cointegration, so, therefore, it is a type of { } transposition.

Answer 22

Replicative

Question 23

What is breakage & reunion?

Answer 23

Mechanism of nonreplicative transposition in which donor remains broken w/ DSB

Question 24

How exactly does nonreplicative transposition result from crossing over?

Answer 24

The crossover structure itself is released by nicking, so a DSB is left behind

Question 25

What does homologous recombination of multiple transposon copies lead to?

Answer 25

Rearrangement of host DNA

Question 26

The reciprocal recombination between the direct repeats causes material to be excised from between the repeats. This mechanism is very similar to... (HINT: site-specific)

Answer 26

Site-specific mitotic homologous recombination via the Cre/lox system

Question 27

What are the 3 steps of transposition in a retrovirus?

Answer 27

1) Reverse transcription 2) Integration 3) Transcription

Question 28

What enzyme is responsible for reverse transcription?

Answer 28

Reverse transcriptase

Question 29

What enzyme is responsible for integration?

Answer 29

Integrase

Question 30

How are retroviral integrases related?

Answer 30

By sequence, structure, and function to the transposase encoded by transposons

Question 31

What are R segments?

Answer 31

Short sequences repeats located at each end of viral RNA

Question 32

What is the purpose of the retroviral gag gene?

Answer 32

Code for protein components of nucleoprotein core of virion

Question 33

What is the purpose of the retroviral pol gene (HINT: pol as in polymerase)?

Answer 33

Nucleic acid synthesis and recombination

Question 34

What is the purpose of the retroviral env gene?

Answer 34

Forming viral envelope

Question 35

What are retroviruses called plus-strand viruses?

Answer 35

Viral RNA itself codes for protein products

Question 36

What is the native primer for retroviral reverse transcription?

Answer 36

tRNA

Question 37

What is the first step of reverse transcription creating DNA?

Answer 37

First, tRNA primer anneals to binding site of RNA

Question 38

Reverse transcription requires that reverse transcriptase synthesize...

Answer 38

DNA strand complementary to the RNA template

Question 39

After reverse transcriptase synthesizes a DNA strand complementary to the RNA template, the RTase then dissociates...

Answer 39

From the RNA template

Question 40

After dissociating from the RNA template, RTase associates...

Answer 40

With another template strand to continue synthesis and form a DNA strand

Question 41

How much of the genome do retroelements make up?

Answer 41

About half of it

Question 42

What are the 3 classes of retroelements?

Answer 42

1) Retrotransposons 2) Retroposons 3) Nonautonomous short-interspersed nuclear elements (SINEs)

Question 43

What is the difference between retrotransposons & retroposons?

Answer 43

Retrotransposons have LTRs while retroposons do not

Question 44

What is the purpose of long-term repeats (LTRs)?

Answer 44

Regulate gene expression via a straight-forward reverse transcription reaction

Question 45

What are short-interspersed nuclear elements (SINEs)?

Answer 45

Elements generated via an RNA-mediated transposition event that do not code for proteins but do have transposition functions

Question 46

What are long-interspersed nuclear elements (LINEs)?

Answer 46

Elements that generate genomic insertions via RNA-mediated retrotransposition