1. © 2017 Pearson Education, Inc. Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge 4 Nucleic Acids EQ: What is the structure and function of nucleic acids?

2. Chapter 4 Opening Roadmap. © 2017 Pearson Education, Inc.

4. Nucleic Acids: Deoxyribonucleic acid (DNA) stores genetic information in cells Ribonucleic acid (RNA) researchers believe was the first life molecule A nucleic acid is a polymer of nucleotide monomers. Nucleotides are the building blocks.

5. © 2017 Pearson Education, Inc. What Is a Nucleotide? Three components of a nucleotide: 1.A phosphate group 2.A five-carbon sugar 3.A nitrogenous (nitrogen-containing) base Both the phosphate group and the nitrogenous base are bonded to the sugar molecule

6. © 2017 Pearson Education, Inc. Nucleotide phosphate 5-C sugar Nitrogen base A – T G – C PurinesPyrimidines Adenine Guanine Cytosine Thymine (DNA) Uracil (RNA) Double ring Single ring

7. © 2017 Pearson Education, Inc. What Is a Nucleotide? RNA nucleotides are the monomers of RNA The sugar is ribose Has an –OH group bonded to the 2′ carbon DNA nucleotides are the monomers of DNA The sugar is deoxyribose (deoxy = “lacking oxygen”) Has an H instead at the 2′ carbon Both of these sugars have an –OH group bonded to the 3′ carbon

8. Figure 4.1 (a) Nucleotide Phosphate group is bonded to 5′ carbon of sugar (c) Nitrogenous bases Nitrogenous base Nitrogenous base is bonded to 1′ carbon of sugar Phosphate group Cytosine (C)Uracil (U) in RNA Pyrimidines Thymine (T) in DNA 5-carbon sugar (b) Sugars Purines are larger than pyrimidines Guanine (G) Purines Adenine (A) Ribose in RNA Deoxyribose in DNA © 2017 Pearson Education, Inc.

9. What Is a Nucleotide? There are two groups of nitrogenous bases: 1. ​ Purines—contain nine atoms in their two rings Adenine (A) Guanine (G) 2. ​ Pyrimidines—contain six atoms in their one ring Cytosine (C) Uracil (U)—found only in RNA Thymine (T)—found only in DNA

10. Figure 4.1 (a) Nucleotide Phosphate group is bonded to 5′ carbon of sugar (c) Nitrogenous bases Nitrogenous base Nitrogenous base is bonded to 1′ carbon of sugar Phosphate group Cytosine (C)Uracil (U) in RNA Pyrimidines Thymine (T) in DNA 5-carbon sugar (b) Sugars Purines are larger than pyrimidines Guanine (G) Purines Adenine (A) Ribose in RNA Deoxyribose in DNA © 2017 Pearson Education, Inc.

11. Forming Polymers Nucleic acids form when nucleotides (monomers) join through dehydration synthesis. Phosphodiester bond - a covalent bond between The phosphate group on the 5′ carbon of one nucleotide And the –OH (hydroxyl) group on the 3′ carbon of another

12. Figure 4.2 Condensation reaction Phosphodiester bond © 2017 Pearson Education, Inc.

13. DNA and RNA Strands Are Directional Phosphodiester bonds form a sugar–phosphate backbone Nucleic acids are directional One end has an unlinked 5′ phosphate group The other end has an unlinked 3′ hydroxyl group The order of nucleotides is written in the 5′  3′ direction

14. Figure 4.3 The sugar–phosphate backbone of RNA 5′ end of nucleic acid 5′ 3′ and 5′ carbons joined by phosphodiester linkage 3′ end of nucleic acid: new nucleotides are added to the unlinked 3′ hydroxyl 3′ © 2017 Pearson Education, Inc.

15. DNA Structure Chemists knew the structure of nucleotides and that DNA has a sugar–phosphate backbone Chargaff established that # of purines = # of pyrimidines Equal number of T’s and A’s; equal number of C’s and G’s Franklin and Wilkins used X-ray crystallography to measure distances between atoms in DNA Predicted a helical structure

16. © 2017 Pearson Education, Inc. DNA Structure James Watson and Francis Crick determined that Two strands are held together by hydrogen bonds between pyramidines and purines. Complementary base pairing occurs between A and T, C and G DNA strands are antiparallel One strand runs 3′  5′, the other runs 5′  3′ DNA strands form a double helix

17. Figure 4.5 (a) Only purine-pyrimidine pairs fit inside the double helix. Purine-purine NOT ENOUGH SPACE Guanine (c) In double-stranded DNA, backbones must run in antiparallel directions. 5′ Cytosine 3′ Pyrimidine-pyrimidine TOO MUCH SPACE Adenine Hydrogen bonds Purine-pyrimidine JUST RIGHT Thymine Space inside sugar- phosphate backbones 3′ Antiparallel strands (b) Hydrogen bonds form between G-C pairs and A-T pairs. 5′ © 2017 Pearson Education, Inc.

18. DNA Structure One turn of the helix occurs every 10 base pairs Hydrophobic interactions in bases causes DNA to twist into a helix Negatively charged phosphate groups face out, making DNA hydrophilic overall DNA has two different-sized grooves: 1.The major groove 2.The minor groove

19. Figure 4.6 (b) Space-filling model of DNA double helix 5′ 3′ Major groove Length of one complete turn of helix (10 rungs per turn) 3.4 nm Minor groove Distance between bases 0.34 nm 5′ Width of helix 2.0 nm 3′ (a) Schematic diagrams of DNA structure 5′ 3′ Hydrogen bonds 3′ Base pairing 5′ Double helix 3′ © 2017 Pearson Education, Inc.

20. DNA Function: DNA can store and transmit biological information DNA carries the information required for growth and reproduction The language of nucleic acids is contained in the sequence of the bases Nitrogenous bases function like letters in an alphabet The sequence of bases has meaning, like the order of letters in a word