AP BIOLOGY

Detailed explanation-1: -A DNA molecule is made up of two linked strands that wind around each other to resemble a twisted ladder in a helix-like shape. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups.

Detailed explanation-2: -Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

Detailed explanation-3: -To avoid bumping into each other, the staircase has to twist a little bit. This turns our staircase into a spiral staircase. This extra twist at the end is the reason for the helical shape. For the “steps” of the DNA “staircase” to fit together, they have to twist a little bit, making the final spiral shape of DNA.