DNA and the Gene: Synthesis & Repair

A set of flashcards for the lecture on DNA structure, synthesis, and repair, covering essential concepts and experimental findings.

What is the primary structure of DNA composed of?

deoxyribonucleotides, which include a phosphate group, a sugar (deoxyribose), and a nitrogenous base.

What are the nitrogenous bases found in DNA?

adenine (A), thymine (T), guanine (G), and cytosine (C).

What is Chargaff's Rule?

In DNA, the amount of adenine (A) equals thymine (T) and the amount of cytosine (C) equals guanine (G).

What does the semiconservative model of DNA replication propose?

Each new DNA molecule consists of one old strand and one new strand.

What are the three hypotheses regarding the mechanism of DNA replication?

Semiconservative, Conservative, Dispersive.

What is the experimental setup of the Meselson-Stahl experiment?

involved growing E. coli in 15N medium, then transferring them to 14N medium and analyzing the DNA after several generations.

What are the results of the Meselson-Stahl experiment after two generations?

There were 1/4 high-density DNA (15N), 3/4 low-density DNA (14N), and all intermediate-density DNA (hybrid).

What type of reaction combines nucleotides to form DNA?

DNA synthesis occurs through a condensation reaction that forms phosphodiester bonds.

Where does DNA replication start in prokaryotes and eukaryotes?

In prokaryotes, DNA replication starts at one origin of replication, while in eukaryotes, it starts at multiple origins of replication.

Why is DNA replication considered discontinuous on the lagging strand?

Replication is discontinuous on the lagging strand due to the antiparallel nature of DNA, requiring the synthesis of Okazaki fragments.

What is the function of helicase in DNA synthesis?

Helicase unwinds the double helix by breaking the hydrogen bonds between base pairs.

How do DNA polymerases contribute to DNA replication?

It synthesizes new DNA strands by adding dNTPs to the 3' end of existing strands.

What is the role of telomerase?

Extends the ends of linear chromosomes to prevent degradation during DNA replication.

What type of damage does UV light cause to DNA?

It forms pyrimidine dimers, leading to kinks in the DNA strand that halt replication.

What is the process of nucleotide excision repair?

Detects errors, cutting out defective bases, and replacing them with correct nucleotides.