1) Which of the following DNA sequences give rise to palindromic double stranded

Question

1) Which of the following DNA sequences give rise to palindromic double stranded DNA? (a) AGCT (b) AAGNCTT (c) AGGA (d) A and B (e) A and C

2) Which of the following modifications is likely to happen to the mRNA in a eukaryotic cell? (a) capping the 5' end (b) addition of poly A tail to 3 end (c) removal of introns (d) all the above

3) A GC rich stem loop followed by six or more U's indicate: (a) heat shock promoter sequence (b) a highly supercoiled sequence (c) a 5S rRNA sequence (d) a termination sequence for transcription (e) a consensus sequence for transcriptional promoter

4) What is the function of restriction enzymes in their native organisms? Why don't they cut up their own DNA?

Explanation / Answer

1. (a) AGCT. This forms the following palindromic sequence. 5'- AGCTTCGA -3' on one strand and 3'- TCGAAGCT -5' on another strand.

2. (d) All of the above. These are common modifications in eukaryotes.

3. (d) a termination sequence for transcription. This is a common termination sequence which is found in bacterial systems and RNA polymerase recognizes it and stops transcription.

4. Restriction enzymes help in the defense mechanism of native organisms. They are involved in cutting the DNA of invading viruses and provide defense to the native organism. The native organisms do not cut their own DNA because of restriction-modification system.The native organism's DNA is hemimethylated by methytransferases which is a marker for self DNA. While other foreign DNA does not have such a marker and is hence digested.

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