There are two types of nucleotides in DNA, pyrimidines and purines. The purines are Adenine and Guanine. Pyrimidines are Thymine and Cytosine. In RNA, Thymine is replaced with Uracil. Purines pair with pyrimidines in a specific order, therefore Adenine pairs with Thymine, and Cytosine pairs with Guanine. Adenine pairs with Uracil only in RNA, not DNA.

For DNA: A nucleotide contains a nitrogenous base (adenine, thymine, cytosine, or guanine), a pentose (five-carbon) sugar (in this case, deoxyribose), and a phosphate group. A nucleo_side_ is simply a nitrogenous base and a sugar. You could also say that a nucleo_tide_ is a nucleo_side_ with an attached phosphate group.

Adenine and Guanine are purines, therefore that answer choice is correct. Thymine and Cytosine are pyrimidines, therefore any answer that involves those choices are incorrect.

Guanine - cytosine and adenine - thymine form "complimentary base pairs." Guanine can only form hydrogen bonds with cytosine and adenine can only form hydrogen bonds with thymine (and vice versa). With that in mind, any base pairing other than those two can be excluded from this answer. Furthermore, cytosine and guanine form a total of three hydrogen bonds together while adenine and thymine only form two. The extra bond between guanine and cytosine makes the pairing about 50% stronger.

Purines are one of the two families of nitrogenous bases, the other being pyrimidines. Purines consist of a double ring structure, while pyrimidines contain only a single ring making them smaller than purines. Adenine and guanine are purines, while their complimentary base pairs (thymine and cytosine) are pyrimidines. If two purines were to pair together, there would be an unstable bulge in the DNA due to a purine-purine pair being slightly larger than purine-pyrimidine complimentary base pairs. If two pyrimidines were to create a pair, there would be a slight pinch in the DNA for the same reasons. The backbone of DNA consists of deoxyribose and phosphate, not the nitrogenous bases.

RNA and DNA both have the bases cytosine, guanine and adenine in common. In RNA, uracil is present in place of thymine which is found in DNA.

The main difference between a nucleotide and a nucleoside is the presence or absence of phosphate group(s). A nucleotide contains one or more phosphate groups, a pentose sugar, and a nitrogenous base. A nucleoside, on the other hand, contains only a pentose sugar and a nitrogenous base; therefore, a nucleotide always contains more phosphate groups than a nucleoside.

When determining the complementary strand, remember that it will be written in the opposite direction of the template strand. This means that the new strand's 5' end will begin at the 3' end of the template strand. The complementary strand will also be composed of the nucleotides that complete the base pairs found in DNA (A-T and C-G).

Template: 5'-GCCTCATGA-3'

Answer: 5'-TCATGAGGC-3'

To see these pairs match up, the 3' end of the answer must align with the 5' end of the template.

Template: 5'-GCCTCATGA-3'

Answer (3'-5'): 3'-CGGAGTACT-5'

Bonds between A-T (adenine and thymine) are held together by 2 hydrogen bonds, while G-C (guanine and cytosine) are held together by 3 hydrogen bonds. Therefore, A-T bonds are weaker, and will separate first when exposed to heat stress. DNA does not contain uracil.

NADH is a coenzyme that functions to carry electrons during metabolism. It is made up of adenine (a nitrogenous base), nicotinamide (a modified nitrogenous base), two phosphate groups, and two pentose sugars. Since it contains nitrogenous bases, phosphate groups, and pentose sugars it is a type of nucleotide.

cAMP, or cyclic adenosine monophosphate, is a second messenger molecule that facilitates signal transduction inside the cell. It is made up of adenine, a phosphate group, and a pentose sugar (ribose); therefore, it is also a type of nucleotide.

Acetylcholine is a type of neurotransmitter that plays a key role in signal transmission between neurons. Acetylcholine does not contain the three essential groups for a nucleotide; therefore, acetylcholine is not a nucleotide.