Nucleic acids such as DNA and RNA contain a series of nucleotides, each of which contains a sugar, a nitrogenous base, and a phosphate group. The sugar and phosphate group form the backbone of the linear chain, while the nitrogenous bases are able to protrude out. When hydridizing with other nucleic acid strands, only certain nitrogenous bases can pair with others. This base pairing is due to hydrogen bonds that form between the two nitrogenous bases, and the number of hydrogen bonds differs depending on what bases are involved.

For both DNA and RNA strands, guanine and cytosine will pair with one another via three hydrogen bonds.

In RNA, the nucleotide thymine is absent, but in its place is the nucleotide uracil. Uracil is able to base pair with adenine via two hydrogen bonds, but this only happens in RNA, not DNA!

In DNA, thymine is present rather than uracil. The thymine found in DNA is also able to base pair with adenine via two hydrogen bonds. Thus, out of all the answer choices, this is the only correct one that can occur within DNA.

While it could be useful to know that the bases are at the core of the DNA while the sugar-phosphate chains are on the outside, it is possible to answer the question without having memorized that fact. The bases (thymine, cytosine, guanine, adenine) are non-polar, and will cluster in the middle of the chain, away from water. They also connect to each other via hydrogen bonding. On the other hand, the sugar-phosphate groups are hydrophilic, and will cluster towards the outside of the molecule.

It is true that DNA is more stable than RNA. While the exact chemical reasons for this are complex, it is useful to know RNA is readily hydrolyzed in basic conditions. In order to make sense of this, remember that DNA acts as the genetic code, and must hold that genetic information for relatively long periods of time. While there are several types of RNA, it typically acts as a messenger, and is degraded after completing its task. While DNA does contain the base thymine and RNA does contain uracil, this is unrelated to the relative stabilities of the two nucleic acids.

The 5' end has a phosphate group, while the 3' end has an . The two strands do, indeed, have opposing polarities; that is, the 5' end of one is positioned next to the 3' end of the other. The sugar-phosphate backbone is on the outside of the molecule, giving it a negative charge. DNA turns once typically every 10.4 pairs, and the distance between the center of nucleotide pairs is about 3.4nm. The adenine (A)-thymine (T) base pair is connected by two hydrogen bonds, and cytosine (C)-guanine (G), three.

The lagging strand is made up of Okazaki fragments due to discontinuous replication. Each of the fragments has its own primer made from RNA that needs to be removed and replaced with dNTPs. The exonuclease performs this function. A ligase comes through immediately after the exonuclease and joins the fragments together. Helicase is the enzyme that separates the DNA strands.

tRNA is synthesized by RNA polymerase III, mRNA is synthesized by RNA polymerase II, and rRNA is synthesized by RNA polymerase I. DNA polymerase I is involved in DNA synthesis, and specifically, has a 5' to 3' exonuclease functionality, which removes RNA primers laid down by primase and replaces them with DNA nucleotides.

Heterochromatin is dark, dense, tightly packed, and rich in repeating segments. It is often in cells that are inactive or less active. As such, heterochromatin is sometimes referred to as "non-coding DNA". Euchromatin, on the other hand, is less tightly packed, and more readily coded. Centromeres are the part of the chromosome that attach to kinetochores during cellular division. Finally, The ends of chromosomes are known as telomeres. Of note, centromeres and telomeres are actually both composed of heterochromatin.

Chargaff's rules state that guanine (G) = cytosine (C) and adenine (A) = thymine (T). Therefore, since the sample contains 35% C, it must also contain 35% G. 100% - 70% (G + C) leaves 30% left for A and T, or 15% T.

Two orthophosphates are connected via anhydride linkage to form the high energy pyrophosphate. This is the "" bond. Glycosidic linkage describes a bond between two or more sugar molecules, not between orthophosphates. This anhydride linkage is made up of single bonds, and not double or triple bonds. An amide bond is the specific chemical name for a peptide bond.

The (melting temperature)of DNA is defined as the temperature at which half of the DNA strands would become denatured. It is known that GC base pairs are kept together via hydrogen bonding at three different locations, compared to hydrogen bonding at just two locations in AT base pairs. Because of this additional interaction, a DNA strand with a higher component of GC base pairs will have a higher than one with a higher component of AT base pairs.