This question is mostly about the differentiations between a nucleoside and a nucleotide. A nucleoside is composed of a nitrogenous base and a ribose or deoxyribose sugar. A nitrogenous base, a ribose/deoxyribose sugar, and a phosphate describe a nucleotide. Remember that nucleosides are incomplete nucleotides, and lack a phosphate group.

Cytosine and guanine, when base paired, have three hydrogen bonds between them. Adenine and thymine only have two. This extra hydrogen bond helps make the cytosine-guanine pair favorable because it increases stability, and reduces bond energy.

Ionic and covalent bonds do not occur between nitrogenous bases in DNA. Covalent bonds are found in the DNA backbone (known as phosphodiester bonds).

Due to DNA's double-helical structure, the nucleotide bases are paired. Adenine is paired with thymine and guanine is paired with cytosine. Chargaff found that there is typically an equivalent number of adenine and thymine bases, and an equivalent number of guanine and cytosine bases. In a given sample of DNA, all adenine residues will have thymine counterparts on the complementary strand, and all cytosine residues will have complementary guanine counterparts. As a result, there will be equal numbers of each residue of the base pair in any sample of double-stranded DNA.

When determining complementary strands, there are a few important points to consider. First, remember that uracil is only found in RNA. We can eliminate any answer choices that contain uracil. Second, remember that DNA is anti-parallel. This means that the 3' end of the template strand must match up with the 5' end of the complementary strand. Flip any answers that have both 3' ends together. Finally, make sure that the bases align correctly. Adenine and thymine should always pair and cytosine and guanine should always pair.

Template strand: 3'-ATTGC-5’

Complementary strand is antiparallel: 5'-_ _ _ _ _-3'

Complementary strand must have right base pairs: 5'-TAACG-3'

An alternate way of writing this answer would be 3'-GCAAT-5'. This answer would still be correct! It would simply need to be flipped, as in the second step outlined above.

DNA is a double stranded molecule that is antiparallel, meaning the 5' end of one strand matches up with the 3' end of the other strand. Nitrogenous bases hold the strands together via hydrogen bonding. These bases are adenine (A), thymine (T), guanine (G), and cytosine (C). Adenine (A) can only pair with thymine (T), and guanine (G) can only pair with cytosine (C).

The correct answer presents two strands that are antiparallel and show proper binding patterns.

5'-CTAGAG-3'

3'-GATCTC-5'

All other answers have an error in base pairing or ordering.

Nucleic acids are one of the main biological macromolecules, and include DNA and RNA. A nucleotide is a DNA monomer, while a ribonucleotide is an RNA monomer. Numerous nucleotides are bonded together by phosphodiester bonds to form a single molecule of DNA. The pattern of nucleotides is used to store and transmit hereditary information. A nucleotide is composed of a phosphate group, a nitrogenous base, and a pentose sugar (deoxyribose).

Cytosine and guanine form three hydrogen bonds with each other, while adenine and tyrosine only form two hydrogen bonds. This means that strands of DNA with a higher percentage of cytosine and guanine will have higher melting points.

Since we are looking for the sequence with the lowest melting point, we want the lowest percentage of cytosine and guanine, and the highest percentage of adenine and thymine.

Since we know that 35% of the bases in the section of DNA are adenine, we can conclude that 35% of the bases are thymine. This is because adenine will always pair with thymine, so there will be just as many thymine bases as adenine bases. Together, adenine and thymine compose 70% of the segment.

This means that 30% of the section is composed of guanine-cytosine pairs.

Since these two bases will be equal in quantity, 15% of the DNA section will be cytosine bases.

Guanine will pair with cytosine. From this knowledge, we can assume that there will be an equal number of guanine and cytosine residues in the sample. Each guanine must have a cytosine counterpart.

The total composition of the DNA sample must be accounted for by the sum of all the bases.

Use the known values for guanine and cytosine to find the sum of adenine and thymine.

Like cytosine and guanine, adenine and thymine must be present in equal amounts in order to form proper base pairs. We can reasonably assume that half of the remaining DNA will consist of each residue.

There are four nitrogenous bases found in DNA: adenine, thymine, cytosine, and guanine. Adenine always binds with thymine, and cytosine always binds with guanine.

Since certain bases always appear in pairs, they will have equal percentages of the DNA composition. The percentage of adenine will equal the percentage of thymine, and the percentage of cytosine will equal the percentage of guanine. Together, these percentages will add to 100%.

We know that the sample is 35% adenine, which tells us that it is also 35% thymine.

We know that cytosine and guanine pair together and will be present in equal amounts, so we can divide this final total by 2 to find our answer.

The sample is 35% adenine, 35% thymine, 15% guanine, and 15% cytosine.