Why are RNA and DNA - RNA hybrids denser than double-stranded DNA? A ribonucleot

Question

Why are RNA and DNA - RNA hybrids denser than double-stranded DNA? A ribonucleotide molecule forms secondary structures that makes whole molecule slightly heavier than a deoxyribonucleotide molecule with thymine base, while the volumes occupied are essentially the same. The uracil base makes ribonucleotide molecule slightly heavier than a deoxyribonucleotide molecule with thymine base, while the volumes occupied are essentially the same. A deoxyribonucleotide molecule tends to form supercoiled structures that makes whole molecule slightly heavier than a ribonucleotide molecule, while the volumes occupied are essentially the same. The oxygen atom at the 2' position of ribose makes a ribonucleotide molecule slightly heavier than a deoxyribonucleotide molecule, while the volumes occupied are essentially the same. Submit Request Answer

Explanation / Answer

Before going to the details of DNA and RNA one should know the simple formula that is

D= M/V

Here D, represent the density and M represent the Molecular mass and V represents the Volume.

If volume will increase than the density must decrease.

If mass will increase for the specified volume then density will increase.

In this question taken each option one by one and decide which option is correct.

1. While forming the secondary structure the volume will decrease then it is possible that density will increase but here they mentioned that volume is essentially same hence this option is not correct.

2. In RNA Uracil base is present that is molecular wt is 112 g/mo/ whereas thyrmin base that is present in DNA only having molecular weight is 126 g/mol. This option is just saying the opposite thing.

3. Similar to first option that supercoiling reduces the volume but in at the end of option the volume will be the same.

4. In ribose sugar, at 2’end, oxygen molecule is present and its molecular weight is 150 g/mol whereas   deoxy ribose suga 134.g/mol. Here molecular weight at given volume is increasing. So molecule become denser.

Here 4th option is correct.

Kindly rate this explanation.

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