10.2 DNA and RNA are polymers of nucleotides DNA is a nucleic acid, made of long chains of nucleotides Phosphate group Nitrogenous base Nitrogenous base (A, G, C, or T) Sugar Phosphate group Nucleotide Thymine (T) Sugar (deoxyribose) DNA nucleotide Polynucleotide Sugar-phosphate backbone Figure 10.2A

DNA has four kinds of bases, A, T, C, and G Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines Purines Figure 10.2B

Nitrogenous base (A, G, C, or U) RNA is also a nucleic acid RNA has a slightly different sugar RNA has U instead of T Nitrogenous base (A, G, C, or U) Phosphate group Uracil (U) Sugar (ribose) Figure 10.2C, D

10.3 DNA is a double-stranded helix James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B

The structure of DNA consists of two polynucleotide strands wrapped around each other in a double helix 1 chocolate coat, Blind (PRA) Figure 10.3C Twist

Hydrogen bonds between bases hold the strands together Each base pairs with a complementary partner A pairs with T G pairs with C

Partial chemical structure Three representations of DNA Hydrogen bond Ribbon model Partial chemical structure Computer model Figure 10.3D

10.4 DNA replication depends on specific base pairing In DNA replication, the strands separate Enzymes use each strand as a template to assemble the new strands A A Nucleotides Parental molecule of DNA Both parental strands serve as templates Two identical daughter molecules of DNA Figure 10.4A

Untwisting and replication of DNA Figure 10.4B

10.5 DNA replication: A closer look DNA replication begins at specific sites Parental strand Origin of replication Daughter strand Bubble Two daughter DNA molecules Figure 10.5A

Each strand of the double helix is oriented in the opposite direction 5 end 3 end P P P P P P P P 3 end 5 end Figure 10.5B

Overall direction of replication 3 DNA polymerase molecule How DNA daughter strands are synthesized 5 end 5 Daughter strand synthesized continuously Parental DNA 5 3 Daughter strand synthesized in pieces 3 P 5 The daughter strands are identical to the parent molecule 5 P 3 DNA ligase Overall direction of replication Figure 10.5C