DNA Flashcards
Q: What evidence supports that DNA carries genetic information?
A: DNA carries genetic information through its sequence of nucleotides (A, T, C, G), which codes for the synthesis of proteins that define an organism’s traits.
: Q: What is the structure of DNA?
A: DNA is an anti-parallel double-stranded polynucleotide. Each strand consists of a backbone of sugar and phosphate groups, with nitrogenous bases (A, T, C, G) in the center. Base-pairing between adenine and thymine (A-T) and cytosine and guanine (C-G) plays a crucial role.
: Q: What does the Meselson-Stahl experiment demonstrate?
A: The Meselson-Stahl experiment demonstrated that DNA replication is semi-conservative, meaning that each new DNA molecule consists of one old (parental) strand and one newly synthesized strand.
Q: What is the role of DNA polymerase and other proteins in DNA replication?
A: DNA polymerase catalyzes the synthesis of new DNA strands by adding nucleotides to the growing chain. Other proteins assist in unwinding the DNA, stabilizing the single strands, and ensuring the replication fork moves smoothly.
Q: Is DNA replication accurate?
A: Yes, DNA replication is very accurate, but rare mistakes, such as errors in base pairing, can lead to mutations.
Q: What happens if there are mistakes during DNA replication?
A: Rare mistakes during DNA replication can lead to mutations, which may affect an organism’s traits. However, DNA has repair mechanisms to correct most of these errors.
Q: What is the semi-conservative nature of DNA replication?
A: In semi-conservative replication, each of the two new DNA molecules contains one strand from the original (parental) DNA molecule and one newly synthesized strand.
Q: What are the leading and lagging strands in DNA replication?
A: The leading strand is synthesized continuously in the 5’ to 3’ direction, while the lagging strand is synthesized discontinuously, forming Okazaki fragments, and is later joined together.
Q: How does DNA repair work?
A: DNA repair mechanisms, such as mismatch repair, help fix errors that occur during replication to maintain genetic stability.
What does helicase do?
It unzips the double helix
What does primase do?
synthesizes RNA primer at 5’ end of leading strand and 5’ end of okazaki fragment
Q: What are the functions of DNA Polymerase I in DNA replication?
Removes RNA primers using 5’ → 3’ exonuclease activity
Replaces RNA with DNA using 5’ → 3’ polymerase activity
What does DNA ligase do?
DNA ligase seals gaps between Okazaki fragments by forming phosphodiester bonds, completing the sugar-phosphate backbone and creating a continuous DNA strand.
Q: What did the Meselson-Stahl experiment demonstrate about DNA replication?
A:
It showed that DNA replication is semi-conservative, meaning each new DNA molecule contains one original (parental) strand and one newly synthesized strand.
Grew bacteria in heavy nitrogen (¹⁵N) → DNA labeled “heavy”
Transferred to light nitrogen (¹⁴N) medium
After 1 generation: 1 intermediate band (rules out conservative)
After 2 generations: 1 light band + 1 intermediate band (supports semi-conservative, not dispersive)
