Podcast
Questions and Answers
Under physiological conditions, which DNA form is the most stable and serves as the standard reference?
Under physiological conditions, which DNA form is the most stable and serves as the standard reference?
- A-DNA
- Z-DNA
- B-DNA (correct)
- A-RNA
Which of the following is a key distinguishing feature of Z-DNA compared to A-DNA and B-DNA?
Which of the following is a key distinguishing feature of Z-DNA compared to A-DNA and B-DNA?
- Z-DNA has a right-handed helix, while A-DNA and B-DNA have a left-handed helix.
- Z-DNA requires a dehydrated environment to form, unlike A-DNA and B-DNA.
- Z-DNA has a zig-zag shape with left-handed helices, and alternating purine residues in the _syn_ configuration. (correct)
- Z-DNA always occurs in cells, while A-DNA and B-DNA do not.
How does the axial rise per base pair in A-DNA compare to that of B-DNA?
How does the axial rise per base pair in A-DNA compare to that of B-DNA?
- Both A-DNA and B-DNA have the same axial rise of 0.34 nm.
- A-DNA has a larger axial rise (0.26 nm) compared to B-DNA (0.34 nm).
- A-DNA has a smaller axial rise (0.26 nm) compared to B-DNA (0.34 nm). (correct)
- A-DNA has a larger axial rise (0.45 nm) compared to B-DNA (0.34 nm).
If a DNA sequence favors the Z-DNA conformation, which glycosidic bond configuration would be expected for its purine bases?
If a DNA sequence favors the Z-DNA conformation, which glycosidic bond configuration would be expected for its purine bases?
Consider a segment of DNA transitioning from B-DNA to A-DNA. Based on the provided information, what changes would you expect to observe in the helical structure?
Consider a segment of DNA transitioning from B-DNA to A-DNA. Based on the provided information, what changes would you expect to observe in the helical structure?
Flashcards
What is B-DNA?
What is B-DNA?
The standard form of DNA under physiological conditions, as described by Watson and Crick.
What is A-DNA?
What is A-DNA?
A dehydrated form of DNA, similar to the structure found in double-helical RNA.
What is Z-DNA?
What is Z-DNA?
DNA that forms a zig-zag shape, with left-handed helices and alternating purine/pyrimidine configurations.
Base pairs per turn for A, B, and Z DNA?
Base pairs per turn for A, B, and Z DNA?
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Glycosidic bond conformation in A, B, and Z DNA?
Glycosidic bond conformation in A, B, and Z DNA?
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Study Notes
- The A, B, and Z forms of DNA are different structural conformations of DNA
- The Watson-Crick structure of DNA is also known as B-DNA
- B-DNA is the most stable structure under physiological conditions
- B-DNA serves as the standard structural reference for random sequence DNA
- A-DNA is a dehydrated form of DNA
- A-DNA may not occur in cells but can exist in double-helical RNA
- Z-DNA takes on a zig-zag shape
- Z-DNA is a left-handed double helix
Conformation Changes in Z-DNA
- Purine residues flip into the syn conformation
- Pyrimidines flip into the anti conformation
Comparison of A-DNA, B-DNA, and Z-DNA Parameters
- Helix sense: A-DNA is right-handed, B-DNA is right-handed, Z-DNA is left-handed
- Shape: A-DNA is the broadest, B-DNA is intermediate, Z-DNA is the narrowwest
- Base pairs per turn: A-DNA has 11, B-DNA has 10, Z-DNA has 12
- Axial rise (nm): A-DNA has 0.26, B-DNA has 0.34, Z-DNA has 0.45
- Helix pitch (nm): A-DNA has 2.6, B-DNA has 3.4, Z-DNA has 4.5
- Base pair tilt (°): A-DNA has 20, B-DNA has -6, Z-DNA has 7
- Twist angle (°): A-DNA has 33, B-DNA has 36, Z-DNA has -30
- Diameter of helix (nm): A-DNA is 2.3, B-DNA is 2.0, Z-DNA is 1.8
- Glycosidic bond conformation: A-DNA is anti, B-DNA is anti, Z-DNA is anti for pyrimidines and syn for purines
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Description
DNA can exist in different structural conformations, including A-DNA, B-DNA, and Z-DNA. B-DNA is the most stable under physiological conditions and serves as the standard reference. A-DNA is a dehydrated form, while Z-DNA has a zig-zag shape with purine residues in the syn conformation and pyrimidines in the anti conformation.
