Question

dna molecules are made up of two strands of nucleotides. strong covalent bonds form 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 hold the two strands together and form the rungs of the dna molecules ladder structure. unlike covalent bonds, weak hydrogen bonds can be easily broken. image of dna structure with labels: sugar - phosphate \backbone\, deoxyribose sugar, nitrogenous bases (adenine, thymine, guanine, cytosine), covalent bond, phosphate group, hydrogen bond complete the paragraph. options: weak hydrogen, deoxyribose sugars, strong hydrogen, nitrogenous bases, weak covalent, strong covalent the structure of a dna molecule resembles a twisted ladder. the rungs of the ladder are formed by blank bonds between the blank. the sides of the ladder, or the backbones of the molecule, are formed by blank bonds between the phosphate groups and the blank.

Explanation:

1. For the first blank (rungs' bonds): From the text, we know hydrogen bonds between nitrogenous bases form the rungs, and hydrogen bonds are weak. So "weak hydrogen" fits.
2. For the second blank (rungs' components): The rungs are between nitrogenous bases, so "nitrogenous bases" is correct.
3. For the third blank (backbone bonds): The text says strong covalent bonds form the backbones, so "strong covalent" is right.
4. For the fourth blank (backbone components): The backbones are between phosphate groups and deoxyribose sugars, so "deoxyribose sugars" is correct.

Answer:

The structure of a DNA molecule resembles a twisted ladder. The rungs of the ladder are formed by \boxed{weak hydrogen} bonds between the \boxed{nitrogenous bases}. The sides of the ladder, or the backbones of the molecule, are formed by \boxed{strong covalent} bonds between the phosphate groups and the \boxed{deoxyribose sugars}.