Question

how is the shape of a dna molecule usually described?
double helix
twisted sister
flattened ladder
twisted spiral

Explanation:

DNA is a biological molecule. In 1953, Watson and Crick proposed the double - helix model of DNA. The double - helix structure consists of two polynucleotide chains that wind around each other like a twisted ladder. The "sides" of the ladder are made of sugar - phosphate backbones, and the "rungs" are made of complementary base pairs (adenine - thymine and cytosine - guanine). The term "twisted sister" is not a scientific description of DNA's shape. A "flattened ladder" does not fully capture the three - dimensional nature of DNA. A "twisted spiral" is too vague compared to the specific double - helix model which is well - established in the field of biology.

Answer:

double helix