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DNA Structure
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Why does a DNA molecule consist of two strands? The primary function of DNA is to store and transmit genetic information. To accomplish this function DNA must have two properties. It must be chemically stable so as to reduce the possibility of damage. DNA must also be capable of copying the information it contains. The two-stranded structure of DNA gives it both of these properties. The nucleotide sequence contains the information found in DNA. The nucleotides connect the two strands through hydrogen bonds. Because each nucleotide has a unique complementary nucleotide, each strand contains all the information required to synthesize a new DNA molecule. The double stranded structure also makes the molecule more stable.

View the animation below, then complete the quiz to test your knowledge of the concept.





1The correct structure of DNA components can be presented as
A)phosphate–base–sugar.
B)phosphate–sugar–base.
C)base–phosphate–sugar.
D)phosphate–sugar–phosphate–base.
E)base–sugar–phosphate–base.


2Which of the following is a characteristic of double-stranded DNA?
A)2 nanometers in width
B)10 base pairs per turn
C)0.34 nanometers per basepair
D)A and B
E)A, B and C


3Which of the following DNA molecules is the most stable?
A)CTGCATAC
GACGTATG
B)GAAATTTC
CTTTAAAG
C)AGTCGAAT
TCAGCTTA
D)GCGTGCAC
CGCACGTG
E)GGATCCTG
CCTAGGAC


4Doubled-stranded DNA consists of two antiparallel strands, meaning that one strand is oriented in the 5’ to 3’ direction, while the other is oriented in the 3’ to 5’ direction.
A)True
B)False


5Asymmetrical spacing of the backbones of the DNA double helix generates major and minor grooves.
A)True
B)False





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