Which of the following statements about DNA are true? The bases are located inside the helix formed from two polynucleotide strands. The grooves all have the same dimensions. The two strands run in the same direction. Within experimental error, the mole percent adenine was always the same as the mole percent thymine, while the mole percent guanine was always the same as that of cytosine.
a) Only statements 1 and 4 are correct.
b) Only statements 1 and 3 are correct.
c) Only statements 1, 2, and 4 are correct.
d) All of the listed statements are correct.

A) Only statmenets 1 and 4 are correct.

Explanation:

DNA or deoxyribonucleic acid is a molecule found in the cell nucleus. It is formed of two chains which are coiled around each other. This coiling is one of the main characteristics of the DNA since it gives a third dimension to the molecule and grooves between every loop. Grooves are known as minor and major depending on the distance between the loops. Chains have different directions and these directions are marked as 3’-5‘ and 5’-3’; so each chain will have 3’-and 5’-end. Every chain is built of  nucleotides and every nucleotide consists of nucleoside and phosphate group. These nucleotides are the basic building blocks for both DNA and RNA (ribonucleic acid), and they are constructed in the way that phosphate groups are located in front and nucleobases are located inside of this double helix. There are several nucleobases and all are separated into two groups according to their chemical structure - Purines (Adenine, Guanine) and Pyrimidines (Thymine, Cytosine) all of which can be found in DNA. There is one more nucleobase called Uracil (Pyrimidine type), this can be found only in the RNA chain. Nucleobases are bonded by hydrogen bonds in combinations: Adenine - Thymine and Guanine - Cytosine with no exceptions, so the amount of Adenine will always be the same as the amount of Thymine in each DNA helix, and the amount of Guanine will always be the same as the amount of Cytosine. The nucleotides are bonded by covalent bonds with one another.