2. Double stranded DNA is a molecule made up of two \'\'strands\'\' of nucleic a

Question

2. Double stranded DNA is a molecule made up of two ''strands'' of nucleic acid. Keeping the distinction between molecule and strand in mind, evaluate the following ''story problem''. A bacterial strain is grown in a heavy nitrogen ^15N environment tor a long enough period that its DNA's nitrogen bases are fully labeled with heavy nitrogen. A sample of that strain is moved to a ^14N environment and allowed to grow two generations. What proportion of the DNA molecules are labeled with both ^14N and ^15N? (5 points) 3. Which RNA poI (I, II, or III) is responsible for making the tRNAs in eukaryotic cells?

Explanation / Answer

ANS. let i will help you.

There are three kinds of RNA in all cells rRNA,mRNA,tRNA.They play key roles in the process of converting nucelotide sequence information into protiens i.e, the tranaslation and during these process RNA polymerase play vital role for their preparation...as below i mentioned which is responsible for which RNA making.

1.RNApoly1...........rRNA

2.RNApol11...........mRNA

3.RNApol111.........tRNA..it transcribes the gene for tRNA.

now, your first problem is related to the semi -conservative nature of DNA as proved by the meselon-stahl experiment. the concept of strand and the molecule is so simple DNA is composite of four bases they are linked by bonds and these makes strands that replicate and then the central dogma starts.the exact method i could not get but, the best is denisty gradient method which will be applied to have the proportion as the N15 is heavy of N14 the outcome is twice is to one .but, according to the semi-conservative nature it will stand stil.

i am sharing a link it will help you to get it better. plz go through it once

http://pablosorigins.blogspot.in/2009/11/dna-replication-part-ii.html

hope you get something

thank you

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