Question

between the phosphate groups and the deoxyribose sugars in each strand to form the backbones\ of the dna molecule.
weak attractive forces, called hydrogen bonds, form between the nitrogenous bases to
the two strands together and form the rungs of the dna molecules ladder structure. unl
covalent bonds, weak hydrogen bonds can be easily broken.

dna structure image with labels: sugar - phosphate \backbone\, deoxyribose sugar, covalent bond, phosphate group, nitrogenous bases (a, t, g, c), hydrogen bond

complete the paragraph.
options: strong hydrogen, strong covalent, deoxyribose sugars, weak hydrogen, weak covalent, nitrogenous bases

the structure of a dna molecule resembles a twisted ladder. the sides of the ladder, or
the backbones of the molecule, are formed by blank bonds between the
phosphate groups and the blank. the rungs of the ladder are formed by
blank bonds between the blank.

Explanation:

• For the backbone: DNA’s sugar - phosphate backbone has covalent bonds (strong, as they are hard to break) between phosphate and deoxyribose sugar (from the diagram and DNA structure knowledge).
• For the rungs: Nitrogenous bases (A - T, C - G) are connected by hydrogen bonds, which are weak (as stated in the given text “weak hydrogen bonds can be easily broken”).

Answer:

1. The sides of the ladder, or the backbones of the molecule, are formed by $\boldsymbol{\text{strong covalent}}$ bonds between the phosphate groups and the $\boldsymbol{\text{deoxyribose sugars}}$.
2. The rungs of the ladder are formed by $\boldsymbol{\text{weak hydrogen}}$ bonds between the $\boldsymbol{\text{nitrogenous bases}}$.