Question

What is the structure of a composite transposon?

a Chromosomal DNA flanked by two direct repeats
b Chromosomal DNA flanked by two IS elements of the same type
c Chromosomal DNA flanked by two inverted terminal repeats
d Antibiotic resistance gene flanked by two inverted terminal repeats

Answer 1

A composite transposon is made up of chromosomal DNA flanked by two identical IS elements, which contain inverted repeats, and can transport DNA, including antibiotic resistance genes, between them when they transpose.

Step-by-step explanation:

The structure of a composite transposon, also known as a Tn element, is characterized by chromosomal DNA that is flanked by two insertion sequences (IS elements) of the same type. These IS elements contain inverted repeats at either end, and they are capable of transposing together, carrying with them any DNA that is located between them. This can include antibiotic resistance genes, allowing for the spread of these genes to other DNA within the cell. Composite transposons are found in low copy numbers in bacterial genomes due to their compact nature, and they can cause the target DNA at the insertion site to duplicate, forming direct repeats of a specific length (not inverted).

Answer 2

A composite transposon consists of chromosomal DNA flanked by two IS elements with inverted terminal repeats, which can include genes like those for antibiotic resistance (option c). Transposition of such elements can spread these genes within the cell.

Step-by-step explanation:

The structure of a composite transposon, also known as a Tn element, involves chromosomal DNA flanked by two Insertion Sequences (IS elements) of the same type, as stated in option b. These IS elements contain inverted terminal repeats, and the DNA that lies between the IS elements can include genes, such as those for antibiotic resistance. When this composite transposon transposes, it can carry and spread these genes within the cell. Notably, apart from the inverted repeats at the ends of the IS elements, the transposition insertion process in host DNA creates direct repeat sequences of host DNA at the site of insertion.

Hence, the answer is option c.