Question

Which of the following statements correctly describes a DNA transposon? Flanking direct repeats are generated when a transposable element inserts into DNA. Transposable elements are mobile DNA sequences. A new copy of a transposable element is introduced at a new site, and the old copy always remains at the original site during replicative transposition. Transposable elements are thought to have played an important role in the evolution of many organisms. All of the above statements correctly describe a DNA transposon.

Answer 1

1. (v) all the above statements correctly describes a DNA transposons.

It is a mobile DNA sequence which can change its position in a genome. It often results in duplication of same genetic material and thus can form the repetitive DNA sequence.whenever a transposable elements are inserted into a DNA it result in the formation of flanking direct repeats in the DNA. It plays very important role in evolution as it brings about the genetic diversity in the population by recombination, chromosomal rearrangements , insertion or deletion in the DNA.

2. (ii) polyribosome .

when a single mRNA is simultaneously translated by more than one ribosomes they are called as polyribosomes or polysomes. Here, each ribosomes are at different stage of progression along the mRNA translating the proteins.

3. ( ii) aminoacyl(A), Exit ( E)

Each ribosomal subunit has three binding sites for transfer RNA and to help in the process of elongation. They are-

1. A (aminoacyl) site - Its function is to accept the incoming amino acylated tRNA

2. P (peptidyl) site - its function is to hold the tRNA with the nascent peptide chain.

3. E (exit) site - its function is to hold the deacylated tRNA before exiting or leaving the ribosome.