AP BIOLOGY

Detailed explanation-1: -A phosphate backbone is the portion of the DNA double helix that provides structural support to the molecule. DNA consists of two strands that wind around each other like a twisted ladder. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups.

Detailed explanation-2: -The backbone of a DNA molecule consists of the phosphate groups and the deoxyribose sugars, whereas the base region of the DNA molecule consists of the nitrogenous bases; therefore, the backbone of DNA is made up of phosphate groups and pentose sugars. Adenine is part of the base region of the molecule.

Detailed explanation-3: -A sugar-phosphate backbone (alternating grey-dark grey) joins together nucleotides in a DNA sequence. The sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA. This backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

Detailed explanation-4: -Answer and Explanation: The sugar-phosphate backbone in a DNA strand within the DNA double helix is located on the outside.

Detailed explanation-5: -The DNA backbone is referred to as the “sugar-phosphate” backbone because it contains deoxyribose groups (the sugars), held together with phosphodiester bonds (each phosphodiester bond contains one phosphate group).