Human Genetics: Concepts and Applications (Lewis), 9th Edition

Chapter 9: DNA Structure and Replication

Chapter Outline

CHAPTER OVERVIEW

1. DNA, the genetic material, contains information the cell requires to synthesize proteins and replicate itself.
2. In 1869, Miescher first isolated DNA and named it "nuclein."
3. In 1902, Archibald Garrod linked heredity to enzyme (protein) defects. In 1909 he published a book entitled "Inborn Errors of Metabolism."

1. In 1928, Griffith identified a "transforming factor" that transmitted infectiousness in bacteria.
2. In 1944, Avery, MacLeod and McCarty showed that the transforming factor was DNA.

1. In 1950, Hershey and Chase, using their famous "blender" experiment, confirmed that DNA, not protein, is the genetic material.

1. The work of chemist Phoebus Levene showed that DNA includes deoxyribose, nitrogenous bases, and phosphates, in equal proportions.
2. Chargaff's data showed that the number of purines equals the number of pyrimidines.
3. Using Rosalind Franklin's X-ray diffraction patterns, Watson and Crick deduced that DNA is a double helix.

1. The gene is a segment of DNA containing the information to specify a sequence of amino acids in a protein. A gene may also encode an RNA that does not code for protein, but is involved in protein synthesis or controlling gene expression.
2. The DNA double helix is a ladder of alternating deoxyribose and phosphate groups, with rungs formed by complementary base pairs.
3. Adenine (A) and guanine (G) are purine bases; cytosine (C) and thymine (T) are pyrimidine bases. A pairs with T, and G with C.
4. The DNA double helix is directional, the two strands are anti-parallel.
5. DNA is highly coiled and wound tightly about histones, forming nucleosomes, which wind into chromatin.

1. Meselson and Stahl in 1957 showed that DNA replication was not conservative or dispersive, but semi-conservative.
2. The two parental strands separate and each is a template for assembling new daughter strands.

1. Replication occurs simultaneously at several points on each human chromosome.
2. At each initiation site, primase builds a short RNA primer. DNA polymerase builds a new strand in the 5' to 3' direction. Bases in the template and complementary bases in the new strand hydrogen bond to form the new double helix.
3. The new strand of DNA is checked for errors and the RNA primers are removed and replaced with DNA bases. Ligase joins the sugar-phosphate backbone.
4. DNA replication is discontinuous because DNA polymerase can't readily replicate strands that run in opposite directions.