Antiparallel means that:
A.the two polynucleotide chains run in opposite directions.
B.each DNA molecule consists of one old and one new strand.
C.opposite strands are held together by base pairing.
D.the helix twists to the right.
E.there is complementary base-pairing
The correct answer is A. Antiparallel means that the two polynucleotide chains (or strands) of DNA run in opposite directions. To arrive at this answer, we need to understand the concept of DNA structure.
DNA is made up of two strands that are twisted around each other to form a double helix. Each strand is composed of a series of nucleotides, which are the building blocks of DNA. Each nucleotide consists of a sugar molecule, a phosphate group, and a nitrogenous base.
In the context of antiparallel strands in DNA, it refers to the directionality of the two strands. One strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction. This means that at one end of the double helix, the 5' end of one strand is next to the 3' end of the other strand. This arrangement of opposite directions is what is meant by antiparallel.
The other answer choices (B, C, D, E) do not accurately describe the concept of antiparallel. Answer B refers to the idea of old and new strands, which is related to DNA replication. Answer C refers to base pairing, which is a characteristic of DNA but not specific to the antiparallel orientation. Answer D refers to the helix twisting to the right, which is true for DNA but not specific to antiparallel orientation. Answer E refers to complementary base pairing, which is a characteristic of DNA but also not specific to antiparallel orientation.
Therefore, the correct answer is A, the two polynucleotide chains of DNA run in opposite directions.