Nucleic Acids

Introduction

• Biology 189: Fundamentals for Life Sciences

• Topic: Nucleic Acids and Inheritance

Learning Objectives

• Understand definitions and functions of nucleic acids:

  • Define nucleic acids and their roles in living organisms.

  • Understand nucleotide structure (the monomers of nucleic acids).

  • Identify five nitrogenous bases and differentiate purines from pyrimidines.

  • Comprehend base pairing between nitrogenous bases.

  • Recognize how nucleotides are joined by phosphodiester linkages.

  • Describe the antiparallel nature of DNA and RNA.

  • Define genes and genomes, and compare similarities and differences between DNA and RNA.

What are Nucleic Acids?

• Definition: Polymers of monomers called nucleotides.

• Types: RNA and DNA.

• Functions:

  • Store genetic information (DNA).

  • Directly involved in protein synthesis (RNA).

Structure of Nucleotides

• Composed of three components:

  • Sugar: Pentose sugar (ribose in RNA, deoxyribose in DNA).

  • Nitrogenous base: Contains various bases outlined below.

  • Phosphate group.

Sugars of DNA and RNA

• RNA: Polymer of nucleotides with ribose sugars.

• DNA: Polymer of nucleotides with deoxyribose sugars.

  

Nitrogenous Bases of Nucleic Acids

• Nitrogenous bases are found in nucleic acids

• Pyrimidines (single ring):

  • Cytosine (C), Thymine (T, in DNA), Uracil (U, in RNA).

• Purines (double ring):

  • Adenine (A), Guanine (G).

    

Joining Nucleotides Together

• Nucleotides are not linked by dehydration synthesis; instead, a condensation reaction occurs. (don’t need to worry about it on test)

• Phosphodiester Linkage:

  • Covalent bond linking two nucleotides.

  • Nucleotides linked by condensation reactions

  • Forms a sugar-phosphate backbone in nucleic acid polymers.

Structure of DNA

• Double Helix: Two DNA strands spiral around each other.

  • Nitrogenous bases pair and strands are antiparallel (opposite directions)

Base Pairing Rules

• Nitrogenous bases pair via hydrogen bonds:

  • Adenine (A) pairs with Thymine (T).

  • Cytosine (C) pairs with Guanine (G).

• Chargaff's Rule:

  • A = # of T; # of C = # of G

DNA Width Maintenance

• Correct width maintained by:

  • Purine + Pyrimidine pairing (consistent width).

  • Purine + Purine or Pyrimidine + Pyrimidine results in inconsistent widths.

Antiparallel DNA Chains

• Strand orientation:

  • Strand 1: 5’ to 3’ direction.

  • Strand 2: 3’ to 5’ direction.

DNA and Genetic Information Storage

• Genome: DNA sequence that encodes info to make protein (book

• Genes: all genes (genetic context) of organism or cell (library)

What is RNA?

• RNA has:

  • Same sugar-phosphate backbone as DNA.

  • Four nitrogenous bases: Guanine (G), Adenine (A), Cytosine (C), and Uracil (U).

  • Typically single-stranded and involved in protein synthesis and gene regulation.

  • Shorter polymers

  • Variable 3D structure

Structure of RNA

• RNA has a variable shape influenced by its primary structure (sequence of nucleotide bases).

• 3D structure due to hydrogen bonds between bases at distant locations within the strand.

Comparing DNA and RNA

Flow of Genetic Information

• Process:

  • DNA undergoes transcription to form mRNA in the nucleus.

  • mRNA is then translated into proteins in the cytoplasm.

Vocabulary

• Nucleotide: Monomer of nucleic acids.

• Nitrogenous Base: Component of nucleotides (A, T, C, G, U).

• Phosphodiester Linkage: Covalent bond in nucleic acids.

• Gene: Sequence of DNA coding for proteins.

• Genome: Complete set of DNA.

• Antiparallel: Orientation of DNA strands.

• Base Pairing: Specific pairing of nitrogenous bases.