Chargaffs Rule # of As = # of Ts # of Cs = # of Gs If its determined that a sample of DNA consists of 23% Adenine, how much of the sample is Guanine? 27%
DNA strands are antiparallel Numbering of strands is based on position of deoxyribose sugars
DNA is wrapped tightly around proteins & folded DNA must unwind for replication to occur
] DNA Replication F occurs during the S phase of Interphase F is semi-conservative (Meselson & Stahl) F Used 14 N and 15 N – different densities
Overview of DNA Replication: Unreplicated DNA. Strands unzip at several points creating replication forks. Each strand serves as template for complementary nucleotides to H-bond. New nucleotides of each daughter strand are linked.
Steps in DNA Replication: Helicase breaks hydrogen bonds. Binding proteins stabilize strands; prevent them from rejoining. Primase makes an RNA primer.
Free nucleotides move in & H-bond; DNA polymerase links nucleotides to each other starting at primer & working in the 5 to 3 direction DNA polymerase proofreads new strand (replaces incorrect bases); leaves errors 1/1,000,000,000 base pairings
DNA replication is continuous on one strand (leading strand) DNA replication is discontinuous on other strand (lagging strand), producing Okazaki fragments