Nucleic Acids Notes

Nucleic Acids

  • Nucleic acids are large molecules (polymers) composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus.
  • They store genetic information and instruct the cell in creating proteins.
  • There are two types of nucleic acids:
    • Deoxyribonucleic Acid, DNA
    • Ribonucleic Acid, RNA
  • The three main types of RNA are:
    • Messenger RNA (mRNA)
    • Transfer RNA (tRNA)
    • Ribosomal RNA (rRNA)

Nucleotides

  • Nucleic acids are composed of chains of nucleotides (monomers).
  • Nucleotides are made up of a sugar, a nitrogenous base, and a phosphate.

Nucleic Acid - DNA

  • DNA consists of two chains of nucleotides.
  • The two chains of nucleotides are formed in opposite directions.
  • The bonds and nitrogenous bases between the two sugar-phosphate backbones are shown.

Nucleic Acid - RNA

  • RNA is similar to DNA but only has a single chain of nucleotides (nucleobases).
  • It also has a different sugar and one different base.

Phosphodiester Bond

  • The bonds between nucleotides are called phosphodiester bonds.
  • Like bonds between monosaccharides, they are formed by dehydration synthesis reactions.
  • The carbon atoms are numbered, and the 3' carbon of one sugar bonds to the 5' carbon of the adjacent sugar through a phosphate group.

Nucleotide Sugars

  • RNA contains the sugar ribose, while DNA contains the sugar deoxyribose.

Bonds

  • The sugar on one nucleotide covalently bonds with the phosphate on the adjacent nucleotide to form a link in the nucleic acid molecule.
  • The nitrogen bases attach to a base on the other chain with hydrogen bonds.

Bonds and DNA Operation

  • Strong covalent bonds in the sugar-phosphate backbone create a strong molecule.
  • Weak hydrogen bonds allow the DNA molecule to be split, copied, and then put together.

Bases

  • RNA contains the bases adenine, guanine, cytosine, and uracil (A,G,C,U).
  • DNA contains the bases adenine, guanine, cytosine, and thymine (A,G,C,T).
  • The difference is that DNA uses thymine (T) rather than uracil (U).

Purines and Pyrimidines

  • Nitrogen-containing bases composed of 2-ringed structures are known as Purines.
  • Nitrogen-containing bases composed of 1-ringed structures are known as Pyrimidines.

DNA

  • DNA is double-stranded.
  • It forms a helix due to the angles of the strong sugar-phosphate bonds; hence, it is called a double helix.
  • Weak hydrogen bonding between nucleotides occurs in DNA between guanine (G) and cytosine (C) and between adenine (A) and thymine (T).

Nucleotide Sequence

  • Each strand is unique due to its sequence of bases.
  • Genetic information is stored in the sequence of nucleotides.
  • Since the bases are not part of the sugar or the phosphodiester bond, the base sequence is independent of the backbone.
  • Any base sequence is possible.

Double Helix

  • Instead of nucleotides being attracted to other bases in the same strand to create shapes, they bond to complementary nucleotides in a second strand to create the double-stranded helix.