DNA Discovery and Structure Quiz

Avery, McCarty, and MacLeod confirmed that DNA is the transforming agent. They repeated Griffith's experiment using isolated DNA, RNA, and proteins, showing that only DNA was capable of transforming non-pathogenic bacteria into pathogenic ones.

Hershey and Chase's experiment used bacteriophages labeled with radioactive isotopes of sulfur (for proteins) and phosphorus (for DNA) to show that DNA is the genetic material. They confirmed that DNA, not protein, was injected into bacteria during infection, demonstrating that DNA carries the genetic information.

Rosalind Franklin used X-ray crystallography to capture images of DNA, revealing its double helix structure. Her data showed that DNA had two strands, was anti-parallel and had a diameter of 2nm.

Watson and Crick used Franklin's X-ray data and Chargaff's rules to build models and propose the double helix structure of DNA, including its anti-parallel orientation and base pairing.

DNA is a double helix composed of two anti-parallel polynucleotide chains. The two strands are held together by hydrogen bonds between complementary nitrogenous bases: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C). The DNA molecule also has a sugar-phosphate backbone, providing structural support.

Chargaff's Rules state that the amount of adenine (A) in DNA is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). These rules helped Watson and Crick understand the base pairing in the double helix.

During DNA replication, the leading strand is synthesized continuously in the 5' to 3' direction, following the opening of the DNA helix. This is because the leading strand is synthesized in the same direction as the replication fork is moving.

The lagging strand is synthesized discontinuously in short fragments called Okazaki fragments, which are later joined together. This is because the lagging strand is synthesized in the opposite direction to the movement of the replication fork, requiring short pieces of DNA to be synthesized backwards.