Nucleic Acid II Flashcards
Which nitrogenous bases pair together in DNA?
Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).
How many hydrogen bonds form between guanine and cytosine?
Three hydrogen bonds
How many hydrogen bonds form between adenine and thymine?
Two hydrogen bonds
Why are the nitrogenous bases called complementary pairs?
Because their shape and functional groups allow them to form stable hydrogen bonds with each other.
What is hybridization in DNA?
Hybridization is the formation of hydrogen bonds between two complementary strands of DNA.
What is the orientation of the two DNA strands in relation to each other?
They are antiparallel; one strand runs 5’ → 3’, while the other runs 3’ → 5’
According to Chargaff’s rules, how do the amounts of purines and pyrimidines compare?
The total amount of purines (A + G) equals the total amount of pyrimidines (T + C).
What technique did Rosalind Franklin and Maurice Wilkins use to study DNA structure?
X-ray diffraction
What did X-ray diffraction data reveal about DNA? (List at least two findings)
(1) DNA is a regular helix, (2) DNA has a repeat distance of 34 angstroms (Å), (3) DNA has a diameter of 20 Å.
What is the length of one complete turn of the DNA helix?
34 Å
What is the diameter of the DNA double helix?
20 Å
What are the two grooves in the DNA helix, and what are their respective sizes?
Major groove (22 Å) and Minor groove (12 Å).
What is the repeat distance in the DNA helix?
34 Å
What is the distance between adjacent nucleotides in DNA?
3.4 Å
In which direction does the DNA double helix twist?
Right-handed (clockwise)
How many base pairs per turn does B-DNA typically have?
10 base pairs per turn
What does it mean when DNA is overwound?
DNA is overwound when it has more than 10 base pairs per turn.
What does it mean when DNA is underwound?
DNA is underwound when it has fewer than 10 base pairs per turn.
What factors can affect the degree of DNA winding?
DNA conformation and protein binding at specific sites.
Why does a high percentage of G-C content make DNA harder to denature?
G-C pairs form three hydrogen bonds, requiring more energy (higher temperature) to separate compared to A-T pairs, which have only two hydrogen bonds.
Why are major and minor grooves important in DNA?
They serve as binding sites for proteins that recognize specific nucleotide sequences.
What types of molecules can interact with the grooves of DNA?
Proteins, recognition molecules, and intercalating agents.
How do denaturing agents like formamide and urea affect DNA structure?
They disrupt hydrogen bonds, causing the DNA strands to separate (denature).
What environmental condition leads to the formation of B-DNA?
High humidity (92%) conditions
