Overview
This lecture covers the structure, components, and functions of nucleic acids, emphasizing differences between DNA and RNA, and highlights their importance in genetics and cell metabolism.
Nucleic Acids: Structure and Components
- Nucleic acids are macromolecules; their monomers are nucleotides.
- DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the primary nucleic acids.
- Each nucleotide consists of a sugar, phosphate group, and nitrogenous base.
- DNA has deoxyribose sugar; RNA has ribose sugar.
- The phosphate group is the same in both DNA and RNA.
- Nitrogenous bases vary: DNA has adenine, guanine, cytosine, and thymine; RNA has adenine, guanine, cytosine, and uracil.
- The specific covalent bond linking nucleotides is the phosphodiester bond.
Nucleotide Structure and Directionality
- Carbons in the sugar are labeled as 1’, 2’, 3’, 4’, and 5’ (prime).
- 1’ carbon bonds to the nitrogenous base; 5’ carbon bonds to the phosphate group.
- DNA lacks an oxygen at the 2’ carbon (“deoxy”); RNA has a hydroxyl group at 2’.
- Nucleic acids are synthesized from the 5’ to 3’ direction; new nucleotides are added to the 3’ end.
- The sugar-phosphate backbone is negatively charged due to the phosphate group.
Nitrogenous Bases and Base Pairing
- Purines (adenine, guanine): two-ring structures; pyrimidines (cytosine, thymine, uracil): single-ring structures.
- Adenine and thymine (DNA) or uracil (RNA) pair together; guanine pairs with cytosine.
- Base pairing in DNA: adenine–thymine (2 hydrogen bonds), guanine–cytosine (3 hydrogen bonds).
- In DNA, each base pair consists of one purine and one pyrimidine, maintaining double helix width.
DNA and RNA Structures
- DNA is double-stranded, forms a double helix, and is antiparallel (opposite 5’ and 3’ orientations).
- Hydrogen bonds between bases allow DNA strands to separate for gene expression.
- RNA is usually single-stranded and can exit the nucleus to assist in protein synthesis.
Important Nucleotides and Cellular Functions
- ATP (adenosine triphosphate) is a key energy molecule, created from ADP and inorganic phosphate.
- NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) are electron carriers essential for metabolism.
- NAD+ and FAD are derived from B vitamins (niacin and riboflavin).
Covalent Bonds in Macromolecules (Review)
- Carbohydrates: glycosidic bond.
- Lipids: ester bond.
- Proteins: peptide bond.
- Nucleic acids: phosphodiester bond.
Key Terms & Definitions
- Nucleotide — Monomer of nucleic acids; consists of sugar, phosphate, and nitrogenous base.
- Phosphodiester bond — Covalent bond linking nucleotides in nucleic acids.
- Purine — Nitrogenous base with two rings (adenine, guanine).
- Pyrimidine — Nitrogenous base with one ring (cytosine, thymine, uracil).
- Antiparallel — Orientation where DNA strands run in opposite directions (5’ to 3’ and 3’ to 5’).
- ATP — Energy-carrying nucleotide with three phosphate groups.
Action Items / Next Steps
- Review lecture slides and practice visual outlines for chapter 3.
- Complete McGraw Hill Connect practice questions for chapters 1-3.
- Study covalent bond types for each macromolecule.
- Prepare for Lecture Quiz 1, focusing on chapter 3.
- Memorize nitrogenous base categories and which occur in DNA/RNA.