1.2 Biologically Important Molecules (Nucleic Acids)

Introduction to Nucleic Acids

• Nucleic acids are essential macromolecules for all known forms of life.

  • Two main types: RNA (Ribonucleic Acid) and DNA (Deoxyribonucleic Acid).

Nucleic Acids Overview

DNA (Deoxyribonucleic Acid)

• Structure:

  • Double-stranded, twisted into a double helix.

• Functions:

  • Stores genetic information.

  • Serves as a blueprint for protein synthesis (DNA → RNA → proteins).

RNA (Ribonucleic Acid)

• Structure:

  • Single-stranded.

• Function:

  • Plays a crucial role in protein synthesis.

Nitrogenous Bases

• Composition: The nucleic acids are composed of nitrogenous bases, sugars, and phosphate groups.

• Types of Bases:

  • Purines: Adenine (A), Guanine (G).

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

Structure of Nucleotides

Components of a Nucleotide

• Nucleotide: The monomer of nucleic acids.

  • Made of:

    • Phosphate group.

    • Sugar (pentose sugar: deoxyribose for DNA, ribose for RNA).

    • Nitrogenous base (A, T, C, G, or U).

Polymerization of Nucleotides

Formation of Polynucleotides

• Polynucleotide: A chain of nucleotides.

  • Held together by covalent bonds known as phosphodiester bonds.

    • Formed between the phosphate group of one nucleotide and the hydroxyl group of the sugar of the next nucleotide.

    • Creates a sugar-phosphate backbone.

• Nucleotide addition occurs in one direction.

  • Nucleotides can only be added to the 3'-OH end.

Hydrogen Bonding and Base Pairing

• Complementary nitrogenous bases bond to stabilize DNA structure:

  • Adenine (A) pairs with Thymine (T) through 2 hydrogen bonds.

  • Cytosine (C) pairs with Guanine (G) through 3 hydrogen bonds.

Orientation of DNA Strands

• DNA strands are antiparallel: One strand runs 5' to 3', while the opposite runs 3' to 5'.