We can use Chargaff's rule to find the remaining compositional percentages. Adenine always pairs with thymine, so their percentages will be equal. Cytosine always pairs with guanine, so their percentages will also be equal. The sum of all four percentages must equal 100%.

We know that the sample is 22% adenine; this tells us it is also 22% thymine.

Since cytosine and guanine are present in equal amounts, we can simply divide their sum by 2.

The final composition is 22% adenine, 22% thymine, 28% cytosine, and 28% guanine.

Uracil is only found in RNA. 

Chargaff's rule only applies to DNA. RNA is single-stranded, and thus, no base pairing occurs.

Think of a strand of DNA. Each base pairs with a specific partner, allowing us to determine their percentages: adenine and thymine are always equal, and cytosine and guanine are always equal. In RNA, with this pairing absent, there is no correlation between the base percentages. A strand could be 20% adenine, 30% guanine, 5% cytosine, and 45% uracil; we simply cannot draw any conclusions.

A polymer is a macromolecule that is made up of subunits that are repeated or very similar. These subunits are called monomers. DNA is a polymer made up of monomer units called nucleotides. Nucleotides are made up of a phosphate group, a five-carbon sugar (deoxyribose, in the case of DNA), and a variable nitrogenous base. There are four different nucleotides that make up the polymer of DNA: thymine, cytosine, adenine, and guanine. These four nucleotides belong to two different classes based on structure. Adenine and guanine are purines that have two carbon-nitrogen rings. Thymine and cytosine are pyrimidines that have only one carbon-nitrogen ring.

Within a DNA molecule, there are specific nucleotide binding patterns, a phenomenon called “complementary base pairing.” Specific pyrimidine nucleotides can only bind to specific purine bases: cytosine binds to guanine via three hydrogen bonds and adenine binds to thymine via hydrogen bonds. Normally, within a DNA molecule, no other base pair combinations exist. These specific complementary base pairs allow DNA to take the form of a double helix. The double helix can be most simply described as a twisted ladder; the base pairs and their hydrogen bonds represent the rungs, and the sugar-phosphate backbone represents the sides of the ladder.

The diagram depicts two purines (adenine and guanine), identifiable by their pyrimidine-imidazole double-ring structure. Pyrimidines (such at thymine and cytosine) have only one ring, amino acids have both amine and carboxylic acid groups, and ribose and deoxyribose are pentameric sugars (and contain no nitrogen).

The bonding that occurs between two parallel strands of nucleic acids in DNA is hydrogen bonding. As you know, hydrogen bonding occurs between molecules containing fluorine, nitrogen and oxygen with other fluorine, nitrogen and oxygen atoms. This is a fairly weak bond but there are so many hydrogen bonds along a strand of DNA making the attachment between the two quite strong, but the two strands can still be separated as needed (during replication and transcription). Adenine and thymine form two hydrogen bonds, while cytosine and guanine form three hydrogen bonds.

There are two types of bases in DNA: purines and pyrimidines. The purines are adenine and guanine. The pyrimidines are cytosine and thymine (note that uracil is also a pyrimidine, but is only found in RNA). Adenine forms two hydrogen bonds with thymine, and guanine forms three bonds with cytosine. As a result, cytosine/guanine-rich regions in DNA require more energy to denature. One was to remember which bases are purines is through the use of the mnemonic "Pure As Gold". Another mnemonic to help you remember which nitrogenous bases are pyrimidines are that: pyrimidines, like pyramids, are sharp, and sharp things CUT (Cytosine, Uracil, and Thymine).

If the imaginary DNA is ten percent adenine, then that means there must be ten percent thymine because they are complementary to one another. The rest of the eighty percent of the DNA strand must be made up of guanine and cytosine. Because they are complementary to each other, half will be guanine and half will be cytosine. This means that there will be forty percent guanine present in the DNA strand.

If the RNA is thirty percent guanine, then that means it must be composed of thirty percent cytosine because they are complementary to each other. The other forty percent of the RNA strand is made up of adenine and uracil. Because they are complementary to each other, half will be adenine and the other half will be uracil. This means that there will be twenty percent uracil present in the RNA strand.

Hydrogen bonds between nucleotides of different strands are crucial for the stability of DNA. Adenine and thymine pair up with two hydrogen bonds between the nucleotides. On the other hand, cytosine and guanine pair up with three hydrogen bonds between the nucleotides.