Unit 1: Biochemistry - #6 Structure and Function of Macromolecules: Nucleic Acids

Nucleic Acids

• Assembly instructions for all proteins in living organisms 

• Includes DNA and RNA 

• DNA and RNA are polymers that are made up of monomer units, these are called nucleotides

• Nucleotides have three parts: 

  • Nitrogenous base 

  • 5-C sugar 

  • Phosphate group (s)

DNA

• Source of genetic information for every living organism 

• Directs all cellular activities and is able to replicate itself so that new cells and organisms can be created

Nitrogenous Base

• Divided into two groups based upon the number of rings in the structure 

  • Purines: Two rings, adenine and guanine 

  • Pyrimidines: One ring, thymine and cytosine

Linkage and Phosphodiester Bonds

• DNA nucleotides are joined together at the phosphate group through phosphodiester bonds between carbon 5 of one molecule to the hydroxyl group at carbon 3 from another molecule 

• Additional nucleotides are always added in the 3 end of the previous nucleotide

Hydrogen Bonds

• DNA is a double stranded molecule where the 2 strands run anti-parallel to each other 

• Hydrogen bonds unite strands of DNA together 

• Adenine will always bind to thymine by 3 hydrogen bonds 

• Guanine and cytosine will always bond together by 3 hydrogen bonds 

• A purine will only pair up with its complementary pyrimidine

RNA

• Single stranded polymer 

• Involved in protein synthesis 

• Composed of: 

  • Ribose sugar 

  • Phosphate group 

  • 4 nitrogen containing bases (C, G, A and U) 

  • All of the bases are the same as those found in DNA except Uracil (uracil replaces thymine in RNA)

RNA Linkages: Phosphodiester Bonds

• Also synthesized in the 5’ to 3’ direction in a condensation reaction 

• A phosphodiester bond forms between phosphate group from one nucleotide and the hydroxyl group from the second nucleotide

Deoxyribose vs. Ribose

. Ribose sugar has a hydroxyl (OH) group at position 2, whereas deoxyribose sugar has a hydrogen (H) atom at position 2.

DNA vs. RNA

DNA is double-stranded, forming a double helix, while RNA is usually single-stranded. The sugar in DNA is deoxyribose, whereas RNA contains ribose.