Explain how and why the following circumstances influence characteristics of temperature-induced DNA melting:
percentage of GC base pairs
urea (forms hydrogen bonds with bases)
sodium chloride (neutralizes negatively charged phosphates)
What will be an ideal response?
GC pairs are composed of three hydrogen bonds and require more energy (heat) to separate than do AT pairs. Urea competes for hydrogen bonds; thus, the bases pair with the urea rather than with each other. This weakens the complementary associations that are required to hold the DNA helix together; thus, less heat is required for melting. The sodium of sodium chloride associates with and neutralizes the strong negative charges on the phosphates. The phosphates do not repel each other with the sodium ion present; thus, the double-stranded structure requires more energy to melt.
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Answer the following statement true (T) or false (F)
Surface tension allows water molecules to do all the following except:
a. transmit light energy. b. resist evaporation. c. form a tight surface layer. d. support small organisms.
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What will be an ideal response?
Which of the following is mismatched?
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