This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
True statements about DNA structure 
Select and explain. 
A. All nucleotides are involved in linkage, B. Antiparallel, C. Parallel, D. Bases are perpendicular to DNA
A: All nucleotides are involved in linkage
Answer: A: All nucleotides are involved in linkage 
Explanation: Nucleotides polymerise by forming bonds between the carbon of the sugar and an oxygen atom of the phosphate. The bases do not take pa in the polymerisation, so the chain is held together by a sugar-phosphate backbone with the bases extending off it. This means that the nucleotides can join together in any order along the chain. Many nucleotides form a polynucleotide. A polynucleotide has a free phosphate group at one end and a free OH group at the other end.