L9 DNA denaturation, mutation, damage, and Repair system Flashcards
Define DNA Denaturation
The process of breaking double-stranded DNA into single strands
What stabilizes the DNA duplex during denaturation?
Enthalpic component stabilizes duplex DNA.
H-bonding between complementary bases and van der Waals attraction between stacked bases
Explain what happens during DNA denaturation
When a DNA solution is heated enough, the double-stranded DNA unwinds and the hydrogen bonds that hold the two strands together weaken and finally break into two higher energy strands.
True or false?
DNA denaturation is not a reversible process.
False.
DNA denaturation is reversible: renaturation is promoted by slow cooling.
Rapid cooling creates a population of single-stranded random coils
During DNA denaturation at low temperatures, ΔG is _______.
ΔG is positive
During denaturation, the DNA double-stranded structure is stabilized both by base pairing and by base stacking interactions. This contribution is largely enthalpic, meaning that ΔH appears to be ______.
positive
Why is the entropy low for the transition from double-strand to random coil during DNA denaturation?
Because the double-stranded structure is much more highly organized than the two separate DNA strands, and therefore can adopt a limitless number of conformations.
During denaturation at low temperatures the term TΔS is _____ than ΔH; therefore, ∆G is _____, and the helix is stable.
TΔS is smaller; ∆G > 0
As the temperature is increased during DNA denaturation, what happens to TΔS and ΔG?
TΔS becomes greater than ΔH, and ΔG becomes negative
True or False?
At higher temperatures the double-stranded structure stays stable and together.
False.
At higher temperatures the double-stranded structure becomes unstable and falls apart.
What does the term Tm mean?
Melting temperature (Tm) at which half of the double-stranded DNA molecules are converted to single-stranded DNA
What determines the melting temperature of a DNA strand?
The length and the specific sequence of a DNA.
- The greater the length of DNA, the higher the Tm
- The higher the GC content of a DNA molecule, the higher its Tm
True or False?
The two antiparallel strands of a DNA double helix can be separated when hydrogen bonding between bases on opposite strands is disrupted by denaturing agents such as pH, ionic strength, and heat.
True
The negatively charged hydroxide ion can pull hydrogen ions from base pairs, forming H bond between two strands, causing the strands to separate at what pH levels?
At a pH less than 2.3 or greater than 11.5
What is another word for DNA renaturation?
Annealing
What happens during the annealing (renaturation) process?
Denatured DNA strands reassemble into a double-stranded DNA helix when denaturing agents are removed. This is effected by cooling.
H bonds form between complementary base pairs. Upon renaturation, viscosity increases.
True or False?
The rate of DNA renaturation is directly proportional to the concentration of complementary sequences.
True
Define a DNA mutation.
Any change introduced into the base sequence of DNA
What are the most common DNA mutations?
Substitution, addition, rearrangement, or a deletion of one or more bases
Mutations introduced into somatic cells can cause
disease or cell death, but these are confined to the affected individual
Mutations introduced into germline cells cause
Inheritable diseases
Define mutagens
Physical agents and chemical reagents that cause mutations
Radiation and chemicals cause what type of mutation?
Exogenous damage.
UV radation causes pyrimidine dimers.
X-Rays can cause double-stranded breaks and translocations
Chemicals cause physical damage or intercalation which cause polyermerase errors
The process that produces a mutation is called ______.
Mutagenesis
