Nucleic Acids Summary

Nucleic Acids

  • First isolated by Friedrich Miescher in 1868.
  • Altman (1889) renamed it as nucleic acid; discovered DNA and RNA.
  • Associated with protein synthesis.
  • Nucleotides are monomers.
  • Nucleotide composition: Pentose sugar, nitrogenous base, and phosphoric acid.

Composition of Nucleic Acids

  • Nitrogenous bases:
    • Purines: Adenine (A), Guanine (G)
    • Pyrimidines: Thymine (T), Cytosine (C), Uracil (U)
  • Phosphoric acid: Forms sugar-phosphate backbone.
  • Sugar: Pentose sugars (ribose or deoxyribose).

Nucleotides, Nucleosides & Nucleobase

  • Nucleotide = Nitrogenous base + Pentose Sugar + Phosphate
  • Nucleoside = Nitrogenous base + Pentose Sugar
  • Nucleobase = Nitrogenous base

DNA

  • Key macromolecules for the continuity of life containing hereditary information.
  • In eukaryotes: Found in the nucleus, mitochondria & chloroplasts.
  • In prokaryotes: Located in the nucleoid.
  • Eukaryotic DNA: Linear chromosomes.
  • Prokaryotic DNA: Smaller, often circular chromosomes.
  • Genes encode protein products.

DNA Properties

  • Watson-Crick base pairs: A pairs with T, C pairs with G, Purine pairs with Pyrimidine.
  • Linear (eukaryotes) or Circular (prokaryotes, mitochondria).
  • Polarity: One end is 3' end, the other is 5' end.
  • Complimentary base pairs: A-T, C-G.
  • Antiparallel direction: One chain is 5-3, other chain is 3-5.
  • Non-coding and repetitive DNA.
  • Denaturation and renaturation properties.

Chargaff's Rule

  • A = T, G = C
  • Purines = Pyrimidines
  • A+T amount / G+C amount varies among organisms but is consistent within different tissues of the same organism.

Watson & Crick's Model of DNA

  • 2 helical nucleotide chains.
  • Strands are anti-parallel.
  • Phosphate molecules on the outer part.
  • Purine pairs with pyrimidine.
  • Two H-bonds for A=T, three for G=C.
  • Strands are complementary.
  • Double helix has major and minor grooves.

Importance of DNA

  • Carries genetic material through replication.
  • Enables synthesis of structural proteins for growth and reproduction.
  • Gene mutations can lead to evolutions.

DNA Replication

  • DNA unwinds, separating the two strands.
  • Single strands act as templates for new strand synthesis.
  • Bases are added until two new DNA strands are produced.
  • Semi-conservative replication: One strand of each daughter DNA comes from parent DNA, and one strand is new.

RNA

  • Ribonucleic Acid
  • Single Stranded

RNA Nucleotides Composition

  1. Ribose sugar (with O in 3rd carbon)
  2. Phosphate group
  3. One of 4 types of bases (all containing nitrogen):
    • Adenine
    • Uracil (only in RNA)
    • Cytosine
    • Guanine

RNA vs DNA

  • RNA is more abundant than DNA.
  • Sugar: RNA has ribose, DNA has deoxyribose.
  • Bases: RNA has uracil (U), DNA has thymine (T).
  • Structure: RNA is single-stranded, DNA is double-stranded.
  • Size: RNA molecules are smaller than DNA molecules.

Types of RNA

  • Ribosomal RNA (rRNA): Most abundant, forms 80% of RNA, found in ribosomes, involved in protein synthesis.
  • Messenger RNA (mRNA): Carries messages from DNA to cytoplasm, forms 5% of RNA.
  • Transfer RNA (tRNA): Carries amino acids to mRNA for protein synthesis, forms 15% of RNA, 60 different types.
  • siRNA (Small Interfering RNA): siRNAs are two stranded, 20-25 bp long, small RNAs which inhibit gene regulation by interacting with mRNA and resulting in its decomposition

Function of RNA

  • All types of RNA are involved in protein synthesis.
  • In certain viruses, RNA forms the genetic materials.
  • rRNA is the main component of ribosome.
  • Some RNA have enzymatic activity.