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Biology A1.2.1 Nucleotides Make Nucleic Acid

Learning Objectives

  1. Understand that DNA is the genetic material of all living organisms.
  2. Identify the components of a nucleotide.
  3. Describe the sugar-phosphate bonding and the sugar-phosphate “backbone” of DNA and RNA.
  4. Explain the bases in each nucleic acid and their role in forming a genetic code.

Part 1: Roles and Features of Nucleic Acids

DNA as genetic materials for all living organisms

  • Genetic material stores information and can be copied and passed from cell to cell and from parent to offspring.
  • Since genetic material is inherited, it is also called hereditary information.
  • All living organisms use DNA to store hereditary information.
  • Some viruses (e.g., coronaviruses and HIV) use RNA as their genetic material.
  • Viruses cannot reproduce on their own and rely on a host cell, so they are not considered true living organisms.
  • This means the claim that all living organisms use DNA as genetic material remains valid.

Types of nucleic acids

  • Nucleic acids were first discovered in the cell nucleus
  • Nucleic acids are large molecules made of nucleotide subunits forming a polymer.
  • Two types of nucleic acids are:
    • DNA (deoxyribonucleic acid)
      • Stores genetic information in all living organisms.
      • Double-stranded helix structure.
      • Contains deoxyribose sugar.
      • Bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
      • Found in:
        • the nucleus, mitochondria, and chloroplasts of eukaryotic cells.
        • in cytoplasm as naked DNA in prokaryotic cells
    • RNA (ribonucleic acid)
      • Involved in protein synthesis and gene regulation.
      • Single-stranded structure.
      • Contains ribose sugar.
      • Bases: adenine (A), uracil (U), cytosine (C), and guanine (G).
      • Found in the nucleus and cytoplasm – depending on the types of RNA:
        • tRNA
        • rRNA
        • mRNA

What are nucleotides?

  • Nucleotides are the monomer (single unit) of nucleic acids.
  • There are many types of nucleotides such as:
    • DNA nucleotides – make DNA
    • RNA nucleotides – make RNA
    • dNTPs – same as DNA nucleotides but with 3 phosphate groups
    • NTPs – same as RNA nucleotides but with 3 phosphate groups
    • ATP – the chemical energy formed by cellular respiration
    • and many more….
  • In general, a nucleotide would have three major components:
    • Pentose sugar
    • Phosphate group
    • Nitrogenous base

Part 2: DNA Backbone and Genetic Bases

Where you can find a the nucleotides in a chromosome

When there are many nucleotides linked together, they will look like a long strand of thread with the nitrogenous bases sticking out.

This makes the sugar – phosphate – sugar – phosphate …. the “backbone”

Note that:

The first nucleotide is linked to carbon-3 of the second nucleotide from its phosphate group. Its phosphate group is located at its carbon-5

  • DNA and RNA each contain four different nitrogenous bases.
    • Three bases are the same in both, but the fourth differs.
  • Bases contain nitrogen, so they are called nitrogenous bases.
  • Each nucleotide has one base, meaning there are four types of nucleotides in both DNA and RNA.
    • Nucleotides can link together because their phosphate and sugar components are the same.
    • Any base sequence is possible, leading to an almost infinite number of sequences in DNA and RNA.
    • The sequence of bases stores genetic information in a coded form.
    • This forms the universal genetic code, shared by all living organisms.

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