Nucleic Acids

Functions of Nucleic Acids

• DNA: stores the genetic code (hereditary information).
• RNA: translates the genetic code into proteins.

Figure 5.26, page 77, Campbell's Biology, 5th Edition

The Basics

A nucleotide is the basic building block of nucleic acids and is composed of three parts:

• Pentose (five-carbon) sugar
  • Ribose
  • Deoxyribose
• Phosphate functional group
• Nitrogenous base
  • Has a nitrogen atom.
  • Is basic (i.e. has a high pH).

Figure 5.27(b), page 78, Campbell's Biology, 5th Edition

Pentose Sugar

• Ribose sugar
  • Used in RNA.
  • Has a hydroxyl functional group (—OH) at carbon 2.
• Deoxyribose sugar
  • Used in DNA.
  • Has no hydroxyl functional group at carbon 2.

Part of figure 5.27(a), page 78, Campbell's Biology, 5th Edition

Nitrogenous Bases

There are two types of nitrogenous bases used in nucleic acids:

• Pyrimidines: one-ringed structure
  • Cytosine
  • Thymine
  • Uracil
• Purines: two-ringed structure
  • Adenine
  • Guanine
• A way to remember the difference: “purines are pure and not CUT.”

Part of figure 5.27(a), page 78, Campbell's Biology, 5th Edition

Nucleotide Polymers

• A nucleotide (pentose sugar + phosphate group + nitrogenouse base) when added in a chain to create a polymer is called a nucleic acid.
• RNA and DNA are polymers of nucleic acids.
• Sugar and phosphates make a “backbone.”
• Nitrogenous bases attached to the sugar at carbon 1.
• Note: the figure below is one strand of DNA.

Part of figure 16.3, page 281, Campbell's Biology, 5th Edition

DNA vs. RNA

Figure 16.5, page 283, Campbell's Biology, 5th Edition

Nonpolymeric Nucleotide Molecules

Some molecules use the nucleotide subunit, but do not form polymers that are acidic in nature.

• ATP
• NAD
• Many others

ATP: Adenosine Triphosphate

• Stores energy for the cell in its phosphate bonds.
• Made of three parts:
  • Sugar: ribose
  • Nitrogenous base: adenine
  • Phosphate groups: three
• Can be converted into ADP (adenosine diphosphate) by the loss of a phosphate group, releasing energy.

Figure 6.6(a), page 89, Campbell's Biology, 5th Edition

NAD: Nicotinamide Adenine Dinucleotide

• Stores energy and transfers electrons.
• Two nucleotides joined together via their phosphate groups.
  • One contains nicotinamide.
  • The other contains adenine.

Part of figure 9.4, page 151, Campbell's Biology, 5th Edition