Question

Read the sources given and answer any four from the questions given below:

Restriction endonucleases are enzymes that are produced by bacteria and cut the double-stranded DNA molecule at specific recognition sequences known as restriction sites. The sequences recognised by endonucleases are typically 4–6 nucleotides long and are palindromes called palindromic nucleotide sequences. A palindrome is a base sequence that reads the same on two strands but in the opposite direction, for example, 5' GAATТС 3', 3' СТТАAG 5'. After cleavage, each DNA strand has a little single-stranded hanging portion at the end. These are called sticky ends. When cut by the same restriction enzyme, the resultant DNA fragments have the same kind of sticky ends which can be joined together by DNA ligases.

1. The function of restriction endonuclease is to
   1. cut RNA at specific restriction sites
   2. cut DNA at specific recognition sequences
   3. form rDNA
   4. cut double-stranded RNA
2. Which of the following sequence is a palindrome?
   1. 5' GAATTC 3', 3' GAATTC 5'
   2. 5' CCATGG 3', 3' GGTACC 5'
   3. 5'AAGCTT 3', 3' GAATTC 5'
   4. 5' GGATCC 3', 5' CCAAGG 3'
3. The overhanging parts of two strands of DNA of cut DNA
   1. are called sticky ends
   2. have single strands of RNA
   3. are of no use for rDNA
   4. are cut and deleted from DNA
4. Function of DNA ligase is to
   1. cut and join DNA
   2. form sticky ends
   3. join fragments of DNA
   4. recognise restriction sites
5. Restriction endonucleases are present in the following
   1. eukaryotes
   2. bacteria
   3. humans
   4. higher plants

Answer 1

1. cut DNA at specific recognition sequences
2. 5' CCATGG 3', 3' GGTACC 5'
3. are called sticky ends
4. join fragments of DNA
5. bacteria