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Introduction to Nucleic Acids: DNA and RNA Informational Molecules

This article introduces nucleic acids, specifically DNA and RNA, as the molecules responsible for storing and transmitting genetic information. It covers the structure and properties of nucleotides, the bases, and their pairings. The importance of complementary base pairing and the double helix structure of DNA are highlighted. Additionally, the role of nucleotide-containing molecules like ATP, NAD+, and FAD in cellular processes is mentioned.

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Introduction to Nucleic Acids: DNA and RNA Informational Molecules

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  1. Macromolecules Part IV: Nucleic Acids Informational molecules

  2. Introduction: Nucleic Acids • The amino acid sequence of a polypeptide is programmed by a gene • A gene consists of regions of DNA, a polymer of nucleic acids (100’s to 1000’s) • DNA (and their genes) is passed by the mechanisms of inheritance • Only molecule that can produce identical copies of themselves

  3. Nucleic acids store and transmit hereditary information • There are two types of nucleic acids: • ribonucleic acid (RNA) • deoxyribonucleic acid (DNA) • DNA provides direction for its own replication • DNA also directs RNA synthesis and, through RNA, controls protein synthesis

  4. ? RolesofDNA • Protein expression (Phenotypes) • Inheritance (Genotypes) 3.Evolution (Mutations)

  5. Nucleotides • Nucleic acids are polymers of monomers called nucleotides • Each nucleotide consists of three parts: • a nitrogen base • a pentose sugar • a phosphate group

  6. Sugar-Phosphate “Backbone”

  7. Nucleic Acids • Polynucleotides are synthesized by connecting the sugars of one nucleotide to the phosphate of the next with a phosphodiester link • The phosphodiester links create a repeating backbone of sugar-phosphate units with the nitrogen bases as appendages

  8. DNA Phosphodiester link RNA

  9. Nucleotides • The nitrogen bases, rings of carbon and nitrogen, come in two types: • Purines • pyrimidines • Pyrimidines have a single six-membered ring • The three different pyrimidines that differ in the atoms attached to the ring: • cytosine (C), thymine (T), and uracil (U) • Purines have a six-membered ring joined to a five-membered ring and there are two types: • adenine (A) and guanine (G)

  10. ? Purine Bases • Adenine and guanine are purines • Purines are the larger of the two types of bases found in DNA

  11. ? Pyrimidine Bases • Cytosine, uracil and thymine are pyrimidines • Mnemonic: Pyramids CUT

  12. Nucleotide Bases Pairings • Because of their shapes, only some bases are compatible with each other • Purines always pair with pyramidines • Adenine (A) always pairs with thymine (T) (in RNA, Adenine pairs with Uracil (U)) • Guanine (G) with cytosine (C)

  13. Counting Carbons

  14. ? Nucleosides VS. Nucleotides • A nucleoside is one of the four DNA bases covalently attached to a sugar • Nucleosides differ from nucleotides in that they lack phosphate groups • A nucleotide is a nucleoside with one or more phosphate groups covalently attached to the sugar group Step 1: Base Step 2: Nucleoside Step 3: Nucleotide

  15. RNA • RNA is made by copying DNA and is used to make proteins • It is a SINGLE strand of nucleotides

  16. DNA • Take two nucleic acid strands • Flip one of the strands • Line the strands together so that they bond • Twist them • Now you have DNA!

  17. DNA: Double Helix Structure • DNA has a double helix structure with two strands that are antiparallel so that nucleotides can form hydrogen bonds One Strand One Strand

  18. H-Bonds But why is it important that the strands are H-bonded and not covalently bonded?

  19. Why H-bonds? • In order to replicate, the strands must separate to make new DNA strands (cannot be broken if the strands were covalently bound)

  20. The sugar-phosphate backbones of the two polynucleotides are on the outside of the helix • Pairs of nitrogenous bases, one from each strand, connect the polynucleotide chains with hydrogen bonds • Most DNA molecules have thousands to millions of base pairs

  21. Nucleotide Bases Pairings • Recap: What are the base-pair rules? • Adenine (A) always pairs with thymine (T) (in RNA, Adenine pairs with Uracil (U)) • Guanine (G) with cytosine (C) • With these base-pairing rules, if we know the sequence of bases on one strand, we know the sequence on the opposite strand • The two strands are complementary

  22. DNA - Base pairing • Adenine and Thymine always bind together • Guanine and Cytosine always bind together

  23. Result: Double Helix Structure

  24. What’s the difference between RNA and DNA? • An RNA molecule is single polynucleotide chain while DNA molecules have two polynucleotide strands that spiral around an imaginary axis to form a double helix • The pentose joined to the nitrogen base is ribose in nucleotides of RNA and deoxyribose in DNA • Nitrogen bases - thymine is replaced by uracil

  25. ATP (adenosine triphosphate) • ATP is a nucleotide that is used to provide energy in cells

  26. NAD+ and FAD • These are nucleotide-containing molecules that function as electron carriers in a variety of cellular processes. NAD+ - nicotinamide adenine dinucleotide FAD- flavin adenine dinucleotide

  27. Home work Study the table on page 30 Do Question on page 31 Questions1-12 Macromolecules Quiz Next Thursday 15th for day 1 classes and Friday 16th for day 2 classes

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