Molecular Biology Flashcards
(9 cards)
Q: How many base pairs per turn are there in B-DNA, and is it left- or right-handed?
A: 10 base pairs per turn, right-handed helix.
Q: Which type of DNA supercoiling facilitates the unwinding of DNA during replication?
A: Negative supercoiling (underwinding the DNA makes it easier to separate strands).
Q: Which groove in B-DNA is wider and typically targeted by DNA-binding proteins?
A: Major groove (wider, more accessible for protein binding).
Q: Which enzyme relieves DNA supercoiling stress during replication by cutting one strand of the DNA?
A: Topoisomerase I.
Q: What interaction provides the greatest contribution to the stability of the DNA double helix?
A: Base stacking interactions (hydrophobic and van der Waals forces between stacked bases).
Q:
What two types of bonds are important in the structure of DNA and where are they found?
A:
• Phosphodiester bonds: link nucleotides in the backbone (strong covalent bonds).
• Hydrogen bonds: hold complementary bases (A-T with 2 bonds, G-C with 3 bonds).
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Q:
According to Chargaff’s Rule, if a DNA molecule has 30% adenine (A), what percentage of guanine (G) would it have?
A:
• 30% adenine = 30% thymine → A + T = 60%
• Remaining 40% = G + C → so guanine = 20%.
Q:
What stabilizes the DNA double helix structure besides hydrogen bonding?
A:
• Base stacking: hydrophobic interactions and van der Waals forces between stacked bases stabilize the helix.
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Q:
What is the directionality (polarity) of DNA strands, and how are the two strands arranged?
A:
• Each strand runs 5’ to 3’.
• DNA is antiparallel: one strand runs 5’→3’, the other 3’→5
