lesson 3

• Nucleic Acids

  DNA & RNA
• What do they do?

  • Dictate amino-acid sequence in proteins
  • Give information to chromosomes, which is then passed from parent to offspring
• What are they?


  • The 4th type of macromolecules
  • The chemical link between generations
  • The source of genetic information in chromosomes
  • The central dogma of molecular biology
• Processes in the transfer of genetic information

  1. Replication: identical copies of DNA are made

  2. Transcription: genetic messages are read and carried out of the cell nucleus to the ribosomes, where protein synthesis occurs

  3. Translation: genetic messages are decoded to make proteins
• The nucleus contains the cell's DNA (genome)
• RNA is synthesized in the nucleus and exported to the cytoplasm
• Ribonucleic acids (RNA)


  The pentose sugar is Ribose (has a hydroxyl group in the 3rd carbon---OH)
• Deoxyribonucleic acids (DNA)


  The pentose sugar is Deoxyribose (has just an hydrogen in the same place---H)
• Nucleic acids


  Polymers of nucleotides
• In eukaryotic cells nucleic acids are either

  • Deoxyribose nucleic acids (DNA)
  • Ribose nucleic acids (RNA)
  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA)
  • Ribosomal RNA (tRNA)
• Nucleotides


  Carbon ring structures containing nitrogen linked to a 5-carbon sugar (a ribose)
• Ribonucleotide


  Nucleotide with a ribose sugar
• Deoxyribonucleotide


  Nucleotide with a deoxyribose sugar
• Nucleic Acid Function


  • DNA: Genetic material - sequence of nucleotides encodes different amino acids
  • RNA: Involved in the transcription/translation of genetic material (DNA)
  • Genetic material of some viruses
• Despite the complexity and diversity of life the structure of DNA is dependent on only 4 different nucleotides
• Diversity is dependent on the nucleotide sequence
• All nucleotides are 2 ring structures composed of

  • 5-carbon sugar: β-D-ribose (RNA), β-D-deoxyribose (DNA)
  • Base: Purine, Pyrimidine
  • Phosphate group
• Nucleotide


  Nitrogeneous base, Pentose, Phosphate
• Nucleoside


  Nitrogeneous base, Pentose
• Nucleobase


  Nitrogeneous base
• Nucleic acids are molecules that store information for cellular growth and reproduction
• Ribonucleotides have a 2'-OH, Deoxyribonucleotides have a 2'-H
• Nucleotide Function


  • Building blocks for DNA and RNA
  • Intracellular source of energy - Adenosine triphosphate (ATP)
  • Second messengers - Involved in intracellular signaling (e.g. cyclic adenosine monophosphate [cAMP])
  • Intracellular signaling switches (e.g. G-proteins)
• Phosphate Groups


  • Phosphate groups are what makes a nucleoside a nucleotide
  • Phosphate groups are essential for nucleotide polymerization
• Number of phosphate groups

  Determines nomenclature: Monophosphate, Diphosphate, Triphosphate
• No free form of Triphosphate exists
• It is the order of these base pairs that determines genetic makeup
• One phosphate + one sugar + one base = one nucleotide
• Nucleotides are the building blocks of DNA – thus, each strand of DNA is a string of nucleotides
• Sanger dideoxy sequencing incorporates dideoxy nucleotides, preventing further synthesis of the DNA strand
• Nucleotide Structure


  • base (purine, pyrimidine)
  • ribose (deoxyribose)
  • N-glycosyl linkage
  • nucleoside+phosphate
  • phosphoester linkage
  • nucleotide
  • phosphodiester linkage
  • nucleic acid
• Sugars


  Ribose, Deoxyribose
• Purine


  Contains 4 N's in a fused-ring structure. Three are basic like pyridine-like and one is like that in pyrrole
• Pyrimidine


  Contains two pyridine-like nitrogens in a six-membered aromatic ring
• Nitrogen Bases


  • Purines: Adenine (A), Guanine (G)
  • Pyrimidines: Cytosine (C), Thymine (T), Uracil (U)
• Thymine is found ONLY in DNA. In RNA, thymine is replaced by uracil
• Uracil and Thymine are structurally similar
• Nucleoside


  Nitrogen base linked by a glycosidic bond to C1' of a ribose or deoxyribose
• Nucleotide


  Nucleoside that forms a phosphate ester with the C5' OH group of ribose or deoxyribose
• Names of Nucleosides and Nucleotides

  • AMP, ADP and ATP