Final answer:
If the eighth nucleotide in the original DNA strand were changed from G to C, the complementary strand will also change. The correct complementary sequence to this mutated strand, when read from the 5' to 3' direction, would be 3'-GCTAGGTA-5', aligning with option 4) CGATGCTA.
Step-by-step explanation:
If the eighth nucleotide in the original DNA strand were changed from guanine (G) to cytosine (C), we must first identify the original sequence before the mutation. Since DNA strands are complementary, a change in the original strand will also alter its complementary strand. DNA bases pair up in a specific way: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Therefore, the complementary base to the mutated cytosine (C) in the original strand will be guanine (G).
Looking at the given sequence options and assuming the original strand started with 5'-CGATCGAT-3', the complementary strand before the mutation would be 3'-GCTAGCTA-5'. If the eighth nucleotide of the original strand is changed from G to C, in the complementary strand, the third nucleotide (counting from the end of the sequence) will change from C to G to maintain the base pairing.
The resulting DNA sequence, therefore, with the change reflected, will be 3'-GCTAGGTA-5', which corresponds to the option 4) CGATGCTA when reading the sequence from the 5' to 3' end.