The nitrogen bases attach to each other according to two simple rules: adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). The exclusivity of the attachments between nitrogen bases is known as base pairing.
The rules of base pairing are frequently tested on the SAT II Biology. A test question might ask, “What is the complementary DNA strand to ‘CAT’?” Following the rules of DNA base pairing, you can deduce that the answer is “CAT.” (“DOG” is the wrong answer, smart guy.)
RNA Structure
Unlike the double-stranded DNA, RNA is single stranded. It looks like a ladder cut down the middle. As you will see when we discuss protein synthesis in the chapter on Cell Processes, this structure of RNA is very important to its functions as a messenger from the DNA in the nucleus to the cytoplasm.
|
DNA |
RNA |
| Bases |
Adenine, guanine, cytosine, thymine |
Adenine, guanine, cytosine, uracil |
| Structure |
Double helix |
Single helix |
| Function |
Stores genetic material and passes it from generation to generation |
Carries messages from the nucleus to the cytoplasm |
Summary of the Molecules of Life
|
Proteins |
Lipids |
Nucleic Acids |
Carbohydrates |
| Function |
Structure, signaling, catalysis |
Energy storage, signaling, membrane constituents |
Store genetic material |
Energy source, energy storage, structural |
| Monomer |
Amino acid |
|
Nucleotide |
Monosaccharide |
| Polymer |
Polypeptide, protein |
|
RNA, DNA |
Polysaccharide |
| Example |
Insulin, transcriptase (an enzyme) |
Corn oil |
A chromosome |
Glucose |
