In the DNA molecule:
Correct answer: B. There are two strands which run antiparallel; one in the 5' ➡ 3' direction and the other in 3' ➡ 5' direction
- A. The proportion of adenine in relation to thymine varies with the organism
- B. There are two strands which run antiparallel; one in the 5' ➡ 3' direction and the other in 3' ➡ 5' direction
- C. The total amount of purine nucleotides and pyrimidine nucleotides is not always equal
- D. There are two strands which run parallel in the 5' ➡ 3' direction
Explanation
A DNA molecule has two unbranched complementary strands, which are spirally coiled. The two chains are antiparallel, i.e., they run parallel but in opposite directions. One chain has the polarity 5' ➡ 3', whereas the other has 3' ➡ 5'. Both are held together by hydrogen bonds between their bases, i.e., A = T and G = C, and the amount of adenine is equal to thymine, and guanine equals cytosine. The base ratio A + T / G + C may vary from one species to another, but is constant for a given species. The purine and pyrimidines are always in equal amounts (A + G = T + C), but A + T is not necessarily equal to G+C.
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Chromosomes are DNA-protein structures that carry genes and become visible during cell division. Coverage includes chromatin, centromeres, sister chromatids, homologous chromosomes, chromosome number, and the distinction between diploid and haploid cells, with links to DNA replication, mitosis and meiosis.
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