Nucleic Acid Structure

Part A

If a strand of DNA has the nitrogen base sequence 5'-ATTTGC-3', what will be the sequence of the matching strand?

	3'-GCAAAT-5'
	3'-ATTTGC-5'
	3'-UAAACG-5'
	3'-TUUUCG-5'
	3'-TAAACG-5'

Correct

Adenine pairs with thymine and guanine pairs with cytosine.

Part B

If a DNA double helix is 100 nucleotide pairs long and contains 25 adenine bases, how many guanine bases does it contain?

	150
	200
	25
	75
	50

Correct

100 nucleotide pairs are a total of 200 nucleotides. Because of base pairing, if there are 25 adenine there must also be 25 thymine. This leaves 200–50 = 150 nucleotides to be divided evenly between guanine and cytosine.

Part C

The two strands of a DNA double helix are held together by _____ that form between pairs of nitrogenous bases.

	hydrophilic interactions
	S—S bonds
	hydrogen bonds
	covalent bonds
	ionic bonds

Correct

Nitrogenous base pairs are joined by hydrogen bonds.

Part D

A nucleotide is composed of a(n) _____.

	phosphate group, a nitrogen-containing base, and a hydrocarbon
	sulfhydryl group, a nitrogen-containing base, and a five-carbon sugar
	phosphate group, a nitrogen-containing base, and a five-carbon sugar
	amino group, a nitrogen-containing base, and a five-carbon sugar
	glycerol, a nitrogen-containing base, and a five-carbon sugar

Correct

These are the components of a nucleotide.