DNA Structure
What overall shape does DNA form?
double helix
Which bases pair together in DNA?
A pairs with T, and G pairs with C.
What does it mean that DNA strands are antiparallel?
They run in opposite 5′ to 3′ directions.
What are the 2 components that make up the backbone of DNA?
sugar and phosphate
Why does DNA maintain a consistent width throughout the helix?
purine always pairs with a pyrimidine.
Which end of a DNA strand has a free phosphate group and which has a free hydroxyl group?
The 5′ end; 3' end
Why is the DNA backbone located on the outside of the helix?
Because it is polar and interacts with the aqueous environment.
Which base pair forms more H bonds & how many?
G-C, 3
Why can DNA polymerase only add nucleotides to one specific end of a growing DNA strand?
Because new nucleotides are added to the free 3′ hydroxyl group.
What interactions help stabilize the DNA double helix?
hydrogen bonds & base stacking interactions (hydrophobic + van de waals forces)
Why are hydrogen bonds important for DNA function?
allow the strands to separate when needed while maintaining stability.
A DNA strand has the following sequence:
5′– A T G C C T A A G T C G A T C G T A C G –3′
Write the complementary strand, including the correct 5′ and 3′ labels.
3′– T A C G G A T T C A G C T A G C A T G C –5′