Transposable Genetic Elements

Question 1

what are transposons?

Answer 1

segments of DNA that are able to move from one part of chromosome to another, or to a different chromosome. they are MUTAGENIC.

“jumping genes”

Question 2

what are the general characteristics of transposable elements?

Answer 2

create staggered breaks in target DNA

INSERTS into DNA

flanking gaps (3-12bp) are filled

Question 3

what does TRANSPOSASE do?

Answer 3

makes a staggered break in DNA and catalyzes transposition

Question 4

what are TERMINAL INVERTED REPEATS

Answer 4

found at the ends of many transposable elements, inverted and complimentary

Question 5

what elements control or limit transposition

Answer 5

METHYLATION OF DNA –> suppresses transcription, prevents production of transposase enzyme

ALTERATIONS IN CHROMOSOME structure –> prevent transcription as they are less accessible to enzymes

PIWI-INTERACTING RNAs (piRNAs) –> bind to piwi proteins and inhibit translation of transposase mRNA

Question 6

what types of mutations can transposable elements cause?

Answer 6

SPONTANEOUS

LOSS OF FUNCTION

GAIN OF FUNCTION

Question 7

how can deletions occur?

Answer 7

pairing of direct repeats causes a loop to form and deletion of the loop

REMEMBER: Direct, Delete (starts with D)

Question 8

how can inversions occur?

Answer 8

crossing over of transposable elements on a gene can cause it to get flipped

forms a U shape

Question 9

how crossing over cause mutations?

Answer 9

a transposable element jumps from one sister chromatid to another

deletion in one, insertion in another

Question 10

what are retrotransposons?

Answer 10

RNA INTERMEDIATE

RNA transcribed from transposable element (DNA)

reverse transcriptase makes a DNA copy of the RNA element

Question 11

what are non-replicative transposons?

Answer 11

CUT AND PASTE

element physically cut out of one site and pasted into another

number of elements preserved

Question 12

what are replicative transposons?

Answer 12

COPY AND PASTE

element is replicated and inserted at a new site

number of elements INCREASES

Question 13

what transposable elements are found in bacteria?

Answer 13

SIMPLE - only carry information required for movement; contain INSERTION SEQUENCE, flanked by DIRECT REPEATS

COMPLEX- contain EXTRA DNA

Question 14

what are COMPOSITE transposons?

Answer 14

any sequence flanked by two transposable elements
flanked by DIRECT repeats
ex. Tn10

Question 15

what are non-composite transposons?

Answer 15

possess transposase gene and have terminal INVERTED repeats
ex. Tn3 (amp resistance)

Question 16

what are the Ac and Ds elements?

Answer 16

transposable elements in CORN

Ac (ACTIVATOR) gene –> terminal inverted sequences, autonomous transposition

Ds (DISSOCIATION) gene –> INACTIVE transposase gene, requires transposase from Ac, NONautonomous transposition

Question 17

what are P elements?

Answer 17

cause HYBRID DYSGENESIS

2900 bp long
terminal inverted repeats
contains a transposase and transposition repressor

Question 18

what is HYBRID DYSGENESIS

Answer 18

caused by repressor protein in FEMALES (not enough cytoplasm in sperm)

P+ female –> inhibits transposition, wild type offspring
P- female –> no inhibitor, mutated offspring

Question 19

what are the transposable elements in humans?

Answer 19

SINES –> RNA intermediates, short flanking repeats

LINES –> longer flanking sequences than SINES