central dogma

• DNA

  Deoxyribonucleic acid
• RNA

  Ribonucleic acid
• Deoxyribonucleic acid (DNA)

  • Chemical component - nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds
• Nucleic acids


  Long, slightly acidic molecules originally identified in cell nuclei that is made up of smaller subunits, linked together to form long chains
• Nucleotides


  Building blocks of nucleic acids that is made up of three basic components (1) 5-carbon sugar (deoxyribose), (2) a phosphate group, (3) a nitrogenous base
• Nitrogenous Bases

  • Thymine
  • Adenine
  • Guanine
  • Cytosine
• Chargaff's Rule


  DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine
• Purines


  • Has double ring where the other has five sides while the other one has six sides
  • Adenine, Guanine
• Pyrimidines

  • Six sides but a single ring structure
  • Thymine, Cytosine
• Deoxyribonucleic acid (DNA)

  The double-helix model explains Chargaff's rule of base pairing and how the two strands of DNA are held together
• Antiparallel Strands


  The two strands of DNA run in opposite directions
• Hydrogen bonds


  Relatively weak chemical forces that could form between certain nitrogenous bases for replication of DNA
• DNA Replication


  Occurs during late interphase of the cell cycle, ensures that each resulting cell has the same complete set of DNA molecules
• Okazaki fragments


  Short DNA nucleotide sequences with an RNA primer at the 5′ end, synthesized discontinuously and later joined by the enzyme DNA ligase to form the lagging strand during DNA replication
• DNA polymerase


  Principal enzyme involved in DNA replication, joins individual nucleotides to produce a new strand of DNA and "proofreads" each new DNA strand
• Helicase


  Unzips DNA enzyme by breaking the hydrogen bond between them
• Three important differences between RNA and DNA:

  1. the sugar in RNA is ribose instead of deoxyribose

  2. RNA is generally single stranded and not double-stranded

  3. RNA contains uracil in place of thymine
• Functions of RNA

  • Most RNA molecules are involved in protein synthesis
  • Controls the assembly of amino acids into proteins
  • 3 main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA
• Messenger RNA


  The RNA molecules that carry copies of instructions for assembling amino acids into proteins, carry information from DNA to other parts of the cell
• Ribosomal RNA


  Forms an important part of both subunits of the ribosome, structural components of the ribosome
• Transfer RNA


  Carries amino acids to the ribosome and matches them to the coded mRNA message
• Transcription


  Segments of DNA serve as templates to produce complementary RNA molecules, base sequences of the transcribed RNA complement the base sequences of the template DNA
• Transcription in eukaryotic cells


  Requires an enzyme, known as RNA polymerase, which uses one strand of DNA as a template to assemble complementary nucleotides into a strand of RNA
• Promoters


  Signals in the DNA molecule that show RNA polymerase exactly where to begin making RNA
• Introns


  Nucleotide sequences in DNA and RNA that do not directly code for proteins, the portions that are cut out and discarded in pre-mRNA
• Exons


  Nucleotide sequences in DNA and RNA that are conserved in the creation of mature RNA
• Protein Synthesis


  Macromolecules composed of units of amino acids, amino acids are bonded covalently to form long linear chains of polypeptides
• Essential amino acids

  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine
• Nonessential amino acids can be synthesized in the body
• Proteins are crucial building blocks of all living things
• Proteins are manufactured (made) by the ribosomes
• Making Proteins

  1. Transcription - carrying genetic information from DNA to RNA

  2. Translation - copying of genetic information from DNA to RNA
• First step: making proteins


  1. Part of DNA temporarily unzips and is used as a template to assemble complementary nucleotides into messenger RNA (mRNA)

  2. mRNA then goes through the pores of the nucleus with the DNA code and attaches to the ribosome
• Second step: making proteins


  Transfer RNA (tRNA) carries amino acids from the cytoplasm to the ribosome
• Central Dogma

  information is transferred from DNA to RNA to protein
• Codon


  • Each three-letter "word" in mRNA
  • a series of three adjacent bases in an mRNA molecule codes for a specific amino acid
  • each tRNA has 3 nucleotides that are complementary to the codon in mRNA
  • mRNA carrying the DNA instructions and tRNA carrying amino acids meet in the ribosomes
  • amino acids are joined together to make a protein