NUCLEIC ACIDS

• Major types of biochemical substances in the human body


  • Nucleic Acids
• Nucleic acid


  Large molecule consisting of long chains of monomers called nucleotides (building block of nucleic acids)

  
• Nucleotide


  Formed from three chemical components: pentose sugar, nitrogen-containing base, phosphate

  
• RNA (Ribonucleic acid)


  Sugar: β-D-Ribose

  
• DNA (Deoxyribonucleic acid)


  Sugar: β-D-2'-Deoxy ribose

  
• Nitrogen Bases


  • Pyrimidines: C, T, and U
  • Purines: A and G

  
• DNA nitrogen bases


  • C, G, A, T
• RNA nitrogen bases


  • C, G, A, U
• Nucleoside


  Has a nitrogen base linked by a glycosidic bond to C1' of a sugar (ribose or deoxyribose)

  
• Nucleotide


  Adding phosphate groups to AMP forms the diphosphate ADP and the triphosphate ATP
• Nucleic acid polymer


  Has a free 5'-phosphate group at one end and a free 3'-OH group at the other end

  
• Nucleic acid polymer is read from the free 5'-end using the letters of the bases

  
• Primary Structure of DNA: 5'—UGCA—3'
• Primary Structure of RNA: 5'—UGCA—3'
• DNA structure


  Double helix consisting of two strands of nucleotides that form a double helix structure like a spiral stair case
• DNA structure


  Has bases along one strand that complement the bases along the other
• Discoverers of DNA: British scientist Francis Crick and American scientist James Watson
• DNA Structure: Chromatin and Chromosomes


  1. DNA/histone wraps around histone proteins

  2. DNA/histone further condenses into a fiber called chromatin

  3. Chromatin can undergo further coiling into its tightest, most compact shape, which is called a chromosome

  
• Humans have a total of 46 chromosomes per cell, 23 from each parent
• Central Dogma


  DNA encodes RNA, RNA encodes Protein
• Central Dogma proposed in 1958 by Francis Crick
• DNA Replication


  1. Helicases unwind and open sections of the double helices

  2. DNA polymerase enzymes catalyze the formation of complementary daughter strands
• In DNA replication, one strand from each of the initial two strands end up in a daughter (new) strand, and each strand serves as a template for a new strand
• Protein synthesis


  1. Transcription

  2. Translation
• Types of RNA


  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA)
  • Ribosomal RNA (rRNA)
  • Heterogeneous nuclear RNA (hnRNA)
  • Small nuclear RNA (snRNA)
• Transcription: Synthesis of mRNA


  1. Informational or coding DNA strand serves as template

  2. RNA polymerase synthesizes complementary mRNA strand
• Post-Transcription Processing: Formation of mRNA

  1. hnRNA produced from a gene through transcription is the precursor for mRNA

  2. Introns are removed from hnRNA to form mature mRNA
• Translation


  Process in which ribosomes synthesize proteins by decoding mRNA
• Genetic Code


  Redundancy - more than one codon codes for each amino acid
• DNA - DNA: A-T, DNA-RNA: A-U
• There are several types of DNA damage that may be due to normal cellular processes or due to the natural exposure of cells to harmful DNA agents
• Mutation


  Change in the structure of a gene caused by mutagens such as radiation and chemicals
• Mutations produce one or more incorrect codons in the corresponding mRNA and a protein that incorporates one or more incorrect amino acids, causing genetic diseases
• Mutagen


  Substance or agent that causes DNA impairment resulting in alteration of the DNA sequence
• Types of Mutations


  • Somatic mutations
  • Germ-line mutations
  • Point mutation (substitution)
  • Frameshift mutations (insertion/deletion)
• Point Mutation


  • Nonsynonymous/missense mutation
  • Nonsense mutation
  • Synonymous/silent mutation
• Frameshift Mutation


  Gain or loss of one or more base pairs, changing the reading frame
• Recombinant DNA technology


  Altering genetic material outside an organism to obtain enhanced and desired characteristics in living organisms or as their products
• Recombinant DNA technology


  Restriction enzymes cleave a gene from a foreign DNA and open DNA plasmids in E. coli

  DNA fragments are mixed with the plasmids in E. coli and the ends are joined by ligase

  The new gene in the altered DNA produces protein
• Recombinant DNA technology is popularly known as genetic engineering