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protein. a, b, thymine. 21, Watson and Crick built models that demonstrated that a, DNA and RNA have the same structure. a double helix. b. DNA is made of two strands that twist into guanine forms hydrogen bonds with adenine. from each ori d. thymine forms hydrogen bonds with cytosine. 22. During DNA replication, a complementary strand of DNA is made will be if a portion of the orig strand is CCTAGCT, then the new a. TTGCATG. C. CCTAGCT. d. GGATCGA. b. AAGTATC. enzymes responsible for adding nucleotides to the exposed DNA bases dur C. helicases. a. d. template enzymes. b. DNA polymerases.

Solution

Answer 21. Option b

Watson and Crick were the first to observe that the DNA molecule exists in a form of a three-dimensional double helix.

Answer 22. Option d

DNA base pairing rule state that in DNA adenine always pairs with thymine while cytosine always pair with guanine.

Answer 23.Option b

DNA ploymerase is a enzyme that is responsible for making new copies of DNA by assembling nucleotides.