Learn About Nucleic Acids and Their Function

DNA structure
DNA structure, from chromosome to deoxyribonucleic acid structure and base pairing. jack0m/DigitalVision Vectors/Getty Images

Nucleic acids are molecules that allow organisms to transfer genetic information from one generation to the next. These macromolecules store the genetic information that determines traits and makes protein synthesis possible.

Key Takeaways: Nucleic Acids

  • Nucleic acids are macromolecules that store genetic information and enable protein production.
  • Nucleic acids include DNA and RNA. These molecules are composed of long strands of nucleotides.
  • Nucleotides are composed of a nitrogenous base, a five-carbon sugar, and a phosphate group.
  • DNA is composed of a phosphate-deoxyribose sugar backbone and the nitrogenous bases adenine (A), guanine (G), cytosine (C), and thymine (T).
  • RNA has ribose sugar and the nitrogenous bases A, G, C, and uracil (U).

Two examples of nucleic acids include: deoxyribonucleic acid (better known as DNA) and ribonucleic acid (better known as RNA). These molecules are composed of long strands of nucleotides held together by covalent bonds. Nucleic acids can be found within the nucleus and cytoplasm of our cells.

Nucleic Acid Monomers

Nucleotide
Nucleotides are composed of a nitrogenous base, a five-carbon sugar, and a phosphate group. OpenStax/Wikimedia Commons/CC BY-SA 3.0

Nucleic acids are composed of nucleotide monomers linked together. Nucleotides have three parts:

  • A Nitrogenous Base
  • A Five-Carbon (Pentose) Sugar
  • A Phosphate Group

Nitrogenous bases include purine molecules (adenine and guanine) and pyrimidine molecules (cytosine, thymine, and uracil). In DNA, the five-carbon sugar is deoxyribose, while ribose is the pentose sugar in RNA. Nucleotides are linked together to form polynucleotide chains. They are joined to one another by covalent bonds between the phosphate of one and the sugar of another. These linkages are called phosphodiester linkages. Phosphodiester linkages form the sugar-phosphate backbone of both DNA and RNA.

Similar to what happens with protein and carbohydrate monomers, nucleotides are linked together through dehydration synthesis. In nucleic acid dehydration synthesis, nitrogenous bases are joined together and a water molecule is lost in the process. Interestingly, some nucleotides perform important cellular functions as "individual" molecules, the most common example being ATP.

DNA Structure

DNA
DNA is composed of a phosphate-deoxyribose sugar backbone and the four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). OpenStax/Wikimedia Commons/CC BY-SA 3.0

DNA is the cellular molecule that contains instructions for the performance of all cell functions. When a cell divides, its DNA is copied and passed from one cell generation to the next generation. DNA is organized into chromosomes and found within the nucleus of our cells. It contains the "programmatic instructions" for cellular activities. When organisms produce offspring, these instructions in are passed down through DNA.

DNA commonly exists as a double stranded molecule with a twisted double helix shape. DNA is composed of a phosphate-deoxyribose sugar backbone and the four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In double stranded DNA, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C).

RNA Structure

RNA
RNA is composed of a phosphate-ribose sugar backbone and the nitrogenous bases adenine, guanine, cytosine and uracil (U). Sponk/Wikimedia Commons

RNA is essential for the synthesis of proteins. Information contained within the genetic code is typically passed from DNA to RNA to the resulting proteins. There are several different types of RNA.

  • Messenger RNA (mRNA) is the RNA transcript or RNA copy of the DNA message produced during DNA transcription. Messenger RNA is translated to form proteins.
  • Transfer RNA (tRNA) has a three dimensional shape and is necessary for the translation of mRNA in protein synthesis.
  • Ribosomal RNA (rRNA) is a component of ribosomes and is also involved in protein synthesis.
  • MicroRNAs (miRNAs) are small RNAs that help to regulate gene expression.

RNA most commonly exists as a single stranded molecule composed of a phosphate-ribose sugar backbone and the nitrogenous bases adenine, guanine, cytosine and uracil (U). When DNA is transcribed into an RNA transcript during DNA transcription, guanine pairs with cytosine (G-C) and adenine pairs with uracil (A-U).

Differences Between DNA and RNA Composition

DNA vs RNA
This image shows a comparison of a single-stranded RNA molecule and a double-stranded DNA molecule. Sponk/Wikimedia Commons/CC BY-SA 3.0

The nucleic acids DNA and RNA differ in composition and structure. The differences are listed as follows:

DNA

  • Nitrogenous Bases: Adenine, Guanine, Cytosine, and Thymine
  • Five-Carbon Sugar: Deoxyribose
  • Structure: Double-stranded

DNA is commonly found in its three dimensional, double helix shape. This twisted structure makes it possible for DNA to unwind for DNA replication and protein synthesis.

RNA

  • Nitrogenous Bases: Adenine, Guanine, Cytosine, and Uracil
  • Five-Carbon Sugar: Ribose
  • Structure: Single-stranded

While RNA does not take on a double helix shape like DNA, this molecule is able to form complex three dimensional shapes. This is possible because RNA bases form complementary pairs with other bases on the same RNA strand. The base pairing causes RNA to fold forming various shapes.

More Macromolecules

  • Biological Polymers: These are macromolecules formed from the joining together of small organic molecules.
  • Carbohydrates: Carbohydrates include saccharides or sugars and their derivatives.
  • Proteins: These macromolecules are formed from amino acid monomers.
  • Lipids: Lipids are organic compounds that include fats, phospholipids, steroids, and waxes.