Chapter 8 - DNA: The Chemical Nature of DNA

What are the three characteristics of good genetic material?

It must contain complex information, replicate faithfully, and encode the phenotype.

Who was Albrecht (“Albert”) Kossel?

A scientist who identified the five nitrogenous bases in nucleic acids.

What did Erwin Chargaff discover?

The base-pairing rules: A = T and G = C in DNA.

What did Miescher discover?

Isolated nuclein from the nuclei of white blood cells (pus) chemical analysis of nuclein revealed that it contained C, H, O, AND the less common N and P.

What did Flemming identify?

“Threadlike bodies” during cell division or chromosomes

What did Sutton discover?

linked chromosomes as the carriers of Mendel’s units of heredity or genes.

What was the contribution of Rosalind Franklin and Maurice Wilkins to DNA research?

They provided X-ray crystallography data that helped reveal DNA’s helical structure.

What did Frederick Griffith discover in 1928?

The “transforming principle” from heat killed S-strain could convert R-strain into a virulent S-strain in mice.

What did Avery, MacLeod, and McCarty conclude from their experiments?

That DNA is the “transforming principle” because only DNase treatment blocked transformation.

What did Hershey and Chase show in their 1952 experiment using bacteriophages?

That DNA, not protein, is the genetic material transmitted to bacteria to make viral progeny.

What are the three components of a DNA nucleotide?

A nitrogenous base, a deoxyribose sugar, and a phosphate group.

What type of bond links nucleotides in a DNA strand?

Covalent phosphodiester bonds.

What type of bond holds the two strands of DNA together?

Hydrogen bonds between complementary nitrogenous bases.

Which bases pair with each other in DNA?

A pairs with T; G pairs with C.

Why is DNA considered a directional molecule?

Because its strands run antiparallel and have distinct 5’ and 3’ ends.

What does “antiparallel” mean in the context of DNA?

The two strands run in opposite direction: one 5’ to 3’ and the other 3’ to 5’.

How is DNA’s coding capacity described?

A DNA molecule of n base pairs can have 4ⁿ combinations.

What form of DNA did Watson and Crick describe?

B-DNA, the most stable form in aqueous conditions.

What is the role of histones in DNA packaging?

DNA wraps around positively charged histone proteins to form nucleosomes.

What is nucleosome?

A DNA-histone complex that appears as "beads on a string" and is a unit of chromatin structure.

What enzyme helps supercoil DNA for compaction?

Topoisomerase.

What is chromatin?

DNA tightly coiled around histones and further compacted into structures within chromosomes.