Which of the following correctly describes what the parts of the DNA molecule are made of?
(Select all that apply.)
backbone—bases
backbone—a phosphate group and a sugar
rungs—bases
rungs—a phosphate group and a sugar
To determine which of the options correctly describes what the parts of the DNA molecule are made of, we need to understand the structure of DNA.
DNA, or deoxyribonucleic acid, is a double-stranded molecule that carries genetic information in all living organisms. It consists of two long strands, often referred to as the "backbone," which are made up of repeating units called nucleotides.
A nucleotide is composed of three main components: a phosphate group, a sugar molecule (deoxyribose in the case of DNA), and a nitrogenous base. The phosphate group and sugar molecule make up the backbone or the sides of the DNA ladder, while the nitrogenous bases form the rungs or steps.
Now let's examine the options provided:
1. Backbone—bases: This option is not entirely correct. The backbone of DNA is made up of the phosphate group and sugar, not the bases.
2. Backbone—a phosphate group and a sugar: This option correctly describes the composition of the DNA backbone. The backbone consists of a phosphate group and a sugar molecule (deoxyribose).
3. Rungs—bases: This option correctly describes the composition of the DNA rungs. The rungs or steps of the DNA ladder are formed by the nitrogenous bases.
4. Rungs—a phosphate group and a sugar: This option is incorrect. The phosphate group and sugar molecules are part of the DNA backbone, not the rungs.
Therefore, the correct options that describe what the parts of the DNA molecule are made of are:
- Backbone—a phosphate group and a sugar
- Rungs—bases