GENETICS ESSENTIALS Concepts and Connections SECOND EDITION GENETICS ESSENTIALS Concepts and Connections SECOND EDITION Benjamin A. Pierce © 2013 W. H. Freeman and Company CHAPTER 8 DNA: The Chemical Nature of the Gene

CHAPTER 8 OUTLINE 8.1 Genetic Material Possesses Several Key Characteristics, All Genetic Information Is Encoded in the Structure of DNA, DNA Consists of Two Complementary and Antiparallel Nucleotide Strands That Form a Double Helix, Large Amounts of DNA Are Packed into a Cell 8.5 Eukaryotic Chromosomes Possess Centromeres and Telomeres 8.6 Eukaryotic DNA Contains Several Classes of Sequence Variation

THE CASE OF NEANDERTHAL AN US Analyses showed that Neanderthals and Humans interbred. On average today humans have 1-4% of Neanderthal DNA

8.1 Genetic Material Possesses Several Key Characteristics Genetic material has to contain complex information. Store large amounts of information Be stable And yet vary Genetic material must replicate faithfully. To be able to transfer correct information to descendents Genetic material must encode the phenotype. The genotype must determine the phenotype

8.2 ALL GENETIC INFORMATION IS ENCODED IN THE STRUCTURE OF DNA Early Studies of DNA DNA As the Source of Genetic Information The discovery of the transforming principle:

DNA As the Source of Genetic Information Identification of the transforming principle: Avery, Macleod, and McCarty’s experiment Fig. 8.2 The Hershey–Chase Experiment Fig All Genetic Information Is Encoded in the Structure of DNA or RNA

8.2 ALL GENETIC INFORMATION IS ENCODED IN THE STRUCTURE OF DNA OR RNA DNA As the Source of Genetic Information Watson and Crick’s discovery of the three-dimensional structure of DNA X-ray diffraction image of DNA

8.3 DNA CONSISTS OF TWO COMPLEMENTARY AND ANTIPARALLEL NUCLEOTIDE STRANDS THAT FORM A DOUBLE HELIX The primary structure of DNA Nucleotides Secondary structures of DNA The double helix Hydrogen bond and base pairing Antiparallel complementary DNA strands

Secondary structure of DNA Different secondary structures: 8.3 DNA Consists of Two Complementary and Antiparallel Nucleotide Strands That Form a Double Helix

8.4 Large Amounts of DNA Are Packed into a Cell Supercoiling Positive supercoiling Fig. 8.16b Negative supercoiling Fig. 8.16c Topoisomerase: The enzyme responsible for adding and removing turns in the coil.

Chromatin Structure Euchromatin Heterochromatin Histone proteins 8.4 Large Amounts of DNA Are Packed into a Cell

Chromatin Structure The nucleosome Chromatosome Linker DNA High-order chromatin structure Epigenetic changes 8.4 Large Amounts of DNA Are Packed into a Cell

Chromatin Structure Centromere structure Telomere structure 8.5 Eukaryotic Chromosomes Possess Centromeres and Telomeres

8.6 EUKARYOTIC DNA CONTAINS SEVERAL CLASSES OF SEQUENCE VARIATION Types of DNA Sequences in Eukaryotes: Unique sequence DNA Gene family: Similar but not identical copies of unique DNA sequences that arose through duplication of an existing gene.

Types of DNA sequences in Eukaryotes: Repetitive DNA Moderately repetitive DNA: 150 ~ 300 bp long. Tandem repeat sequences Interspersed repeat sequences Short interspersed elements: SINEs : Alu element Long interspersed elements: LINEs. Highly repetitive DNA: less than 10 bp long. 8.6 Eukaryotic DNA Contains Several Classes of Sequence Variation