Understanding DNA, RNA, and Chromosomes: a Comprehensive Overview

1. Cell Biology I. Overview II. Membranes: How Matter Get in and Out of Cells III. Cellular Respiration IV. Photosynthesis V. DNA, RNA, and Chromosome Structure

2. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure Avery, McCarty, and MacLeod Chase and Hershey

3. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure Watson and Crick Pauling Wilkins Franklin

4. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure DNA is the genetic material in all forms of life (eubacteria, archaea, protists, plants, fungi, and animals). Those quasi-living viruses vary in their genetic material. Some have double-stranded DNA (ds-DNA) like living systems, while others have ss-DNA, ss-RNA, and ds-RNA. RNA performs a wide array of functions in living systems. Many of these functions have only been discovered in the last few years.

5. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” three parts: - pentose sugar (ribose in RNA, deoxyribose in DNA)

6. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” three parts: - pentose sugar (ribose in RNA, deoxyribose in DNA) - nitrogenous base (A, C, G, U in RNA A, C, G, T in DNA)

7. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” three parts: - pentose sugar - nitrogenous base Nitrogenous base binds to the 1’ carbon

8. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” three parts: - pentose sugar - nitrogenous base - phosphate group PO4 binds to the 5’ carbon

9. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” three parts: - pentose sugar - nitrogenous base - phosphate group Diphosphates and triphosphates occur, also. In fact, here is ATP, the energy currency of the cell. The nucleotides exist as free triphosphates before they are linked into a nucleic acid chain.

10. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ Between the PO4 (which always has free H+ ions binding and unbinding) of the free nucleotide and the –OH group on the 3’ carbon of the last sugar in the chain. OH OH O-P-O O OH O-P-O O OH O-P-O O H2O OH Energy released by cleaving the diphosphate group can be used to power the dehydration synthesis reaction

11. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ Polymerization results in a polymer of DNA (or RNA). This single polymer is a single-stranded helix It has a ‘polarity’ or ‘directionality’; it has different ends… there is a reactive phosphate at one end (5’) and a reactive –OH at the other (3’). So, the helix has a 5’-3’ polarity. 5’ 3’

12. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ 3. most DNA exists as a ‘double-helix’ (ds-DNA) (although some viruses have genetic material that is signle-stranded DNA (ss-DNA)) a. The nitrogenous bases on the two helices are ‘complementary’ to one another, and form weak hydrogen bonds between the helices. A purine (A or G) always binds with a pyrimidine (T or C) In fact, A with T (2 h-bonds) And G with C (3 h-bonds)

13. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ 3. most DNA exists as a ‘double-helix’ (ds-DNA) a. bases are complementary b. the strands are anti-parallel: they are aligned with opposite polarity 5’

15. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ 3. most DNA exists as a ‘double-helix’ (ds-DNA) 4. RNA performs a wide variety of functions in living cells: a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein

16. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ 3. most DNA exists as a ‘double-helix’ (ds-DNA) 4. RNA performs a wide variety of functions in living cells: a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein b. R-RNA is made the same way, is IN the Ribosome, and ‘reads’ the m-RNA

17. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ 3. most DNA exists as a ‘double-helix’ (ds-DNA) 4. RNA performs a wide variety of functions in living cells: a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein b. r-RNA is made the same way, is IN the Ribosome, and ‘reads’ the m-RNA c. t-RNA is made the same way, and brings amino acids to the ribosome

18. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ 3. most DNA exists as a ‘double-helix’ (ds-DNA) 4. RNA performs a wide variety of functions in living cells: a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein b. r-RNA is made the same way, is IN the Ribosome, and ‘reads’ the m-RNA c. t-RNA is made the same way, and brings amino acids to the ribosome d. mi-RNA (micro-RNA) and si-RNA (small interfering RNA) bind to m-RNA and splice it; inhibiting the synthesis of its protein. This is a regulatory function.

19. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure 1. monomers are “nucleotides” 2. polymerization occurs by ‘dehydration synthesis’ 3. most DNA exists as a ‘double-helix’ (ds-DNA) 4. RNA performs a wide variety of functions in living cells: a. m-RNA is a ‘copy’ of a gene, read by the ribosome to make a protein b. r-RNA is made the same way, is IN the Ribosome, and ‘reads’ the m-RNA c. t-RNA is made the same way, and brings amino acids to the ribosome d. mi-RNA (micro-RNA) and si-RNA (small interfering RNA) bind to m-RNA and splice it; inhibiting the synthesis of its protein. This is a regulatory function. e. Sn-RNA (small nuclear RNA) are short sequences that process initial m-RNA products, and also regulate the production of r-RNA, maintain telomeres, and regulate the action of transcription factors. Regulatory functions.

20. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure B. Chromosome Structure 1. Prokaryotes - usually one circular chromosome, tethered to the membrane, with some associated, non-histone proteins.

21. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure B. Chromosome Structure 1. Prokaryotes 2. Eukaryotes – usually many linear chromosomes, highly condensed with histone proteins into several levels of structure.

22. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure B. Chromosome Structure 1. Prokaryotes 2. Eukaryotes – usually many linear chromosomes, highly condensed with histone proteins into several levels of structure. a. Level 1: ds-DNA is wrapped around histone proteins, creating the “beads on a string’ level of organization.

23. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure B. Chromosome Structure 1. Prokaryotes 2. Eukaryotes – usually many linear chromosomes, highly condensed with histone proteins into several levels of structure. • Level 1: ds-DNA is wrapped around histone proteins, creating the “beads on a string’ level of organization.

24. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure B. Chromosome Structure 1. Prokaryotes 2. Eukaryotes – usually many linear chromosomes, highly condensed with histone proteins into several levels of structure. • Level 1: ds-DNA is wrapped around histone proteins, creating the “beads on a string’ level of organization. • Level 2: string is coiled, 6 nucleosomes/turn (solenoid)

25. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure B. Chromosome Structure 1. Prokaryotes 2. Eukaryotes – usually many linear chromosomes, highly condensed with histone proteins into several levels of structure. • Level 1: ds-DNA is wrapped around histone proteins, creating the “beads on a string’ level of organization. • Level 2: string is coiled, 6 nucleosomes/turn (solenoid) • Level 3: the coil is ‘supercoiled’

26. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure B. Chromosome Structure 1. Prokaryotes 2. Eukaryotes – usually many linear chromosomes, highly condensed with histone proteins into several levels of structure. • Level 1: ds-DNA is wrapped around histone proteins, creating the “beads on a string’ level of organization. • Level 2: string is coiled, 6 nucleosomes/turn (solenoid) • Level 3: the coil is ‘supercoiled’ • Level 4: the supercoil is folded into a fully condensed metaphase chromosome

27. V. DNA, RNA, and Chromosome Structure A. DNA and RNA Structure B. Chromosome Structure 1. Prokaryotes 2. Eukaryotes – usually many linear chromosomes, highly condensed with histone proteins into several levels of structure. To read a gene, the chromosome must be diffuse (uncondensed) in that region. Even when condensed, these ‘euchromatic’ coding regions are less condensed and more lightly staining than non-coding regions. DNA that has few genes can remain condensed and closed (heterochromatic), and appears as dark bands on condensed chromosomes.

28. Study Questions: 1) Diagram the parts of an RNA nucleotide. 2)  Show how two nucleotides are linked together by dehydration synthesis reactions. 3) Why does the purine - pyrimidine structure relate to the complementary nature of double-stranded DNA? 4)  Draw a DNA double helix, showing three base pairs and the antiparallel nature of the helices. 5) Describe the higher levels of eukaryotic chromosome structure, including the terms nucleosome and solenoid. 6) What are two differences between euchromatin and hetochromatin?