GENBIO2

• DNA is the blueprint for life
• DNA


  Deoxyribonucleic Acid
• DNA


  • A polymer of nucleotides
  • Each nucleotide composed of a sugar, a phosphate, and a nitrogenous base
• Four DNA bases


  • Purine bases
  • Pyrimidine bases
• Adenine pairs with


  Thymine
• Cytosine pairs with


  Guanine
• DNA


  • A double helix
• DNA Replication


  1. DNA topoisomerase untagles the coils

  2. Helicase "unzips" the DNA molecule exposing both strands

  3. DNA polymerase pairs the bases A-T and G-C

  4. DNA polymerase checks work and corrects mistakes

  5. DNA ligase bonds the nucleotides together
• DNA replication is fast and accurate, with an error occurring in only about one of a billion nucleotides
• DNA replication begins at specific sites called origins of replication, and the copying proceeds outward in both directions, creating replication "bubbles"
• A eukaryotic DNA molecule has many origins where replication can start at the same time, shortening the total time to copy all the DNA
• DNA replication occurs before a cell divides, ensuring that the cells in a multicellular organism all carry the same genetic information, and it is also the mechanism for producing the DNA copies that offspring inherit from parents during reproduction
• The resulting double-stranded DNA molecules are identical, and proofreading and error-checking mechanisms exist
• RNA


  Ribonucleic Acid
• Differences between RNA and DNA

  • RNA contains the sugar ribose instead of deoxyribose
  • RNA bases are A, G, C, and U (Uracil) instead of T
• RNA is single stranded and shorter than DNA
• Central Dogma


  DNA -> RNA -> Proteins
• Three different RNA molecules involved in protein synthesis

  • mRNA (messenger RNA)
  • rRNA (ribosomal RNA)
  • tRNA (transfer RNA)
• Protein Synthesis


  1. Transcription (occurs in the nucleus)

  2. Translation (occurs in the cytoplasm)
• Codon


  Three consecutive bases on the mRNA that specify an amino acid
• The genetic code consists of 64 codons, but only 61 code amino acids, and three codons act as a signal to stop the process
• One codon, AUG, codes for methionine, and is also the Start signal for translation
• Proteins


  Make up all living materials
• Composition of proteins


  • Amino acids (20 different amino acids)
  • Different proteins are made by combining these 20 amino acids in different combinations
• Protein manufacturing


  Ribosomes
• Functions of proteins


  • Help fight disease
  • Build new body tissue
  • Enzymes used for digestion and other chemical reactions (enzymes speed up the rate of a reaction)
  • Component of all cell membranes
• Protein Synthesis


  1. Transcription (copying of genetic information from DNA to RNA)

  2. Translation (decoding of mRNA into a protein)
• Transcription


  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
• Translation


  1. Transfer RNA (tRNA) carries amino acids from the cytoplasm to the ribosome

  2. A series of three adjacent bases in an mRNA molecule codes for a specific amino acid (codon)

  3. Each tRNA has 3 nucleotides that are complementary to the codon in mRNA

  4. Each tRNA codes for a different amino acid

  5. mRNA carrying the DNA instructions and tRNA carrying amino acids meet in the ribosomes

  6. Amino acids are joined together to make a protein (Polypeptide = Protein)
• Proteins we eat are broken down into individual amino acids and then simply rearranged into new proteins according to the needs and directions of our DNA
• DNA gets all the credit, but RNA is also very important
• DNA


  • Has a beautiful double helix structure
  • Stores genetic information and codes for traits
• RNA


  Allows the genetic message to be expressed so cells can produce proteins
• RNA is hypothesized to have come before DNA in the RNA World hypothesis
• Similarities between DNA and RNA

  • Found in all living organisms
  • Both are nucleic acids with nucleotides as monomers
• Differences between DNA and RNA

  • DNA is generally double-stranded, RNA is generally single-stranded
  • DNA has deoxyribose sugar, RNA has ribose sugar
  • DNA bases are A, T, G, C, RNA bases are A, U, G, C
• Types of RNA


  • mRNA (messenger RNA)
  • rRNA (ribosomal RNA)
  • tRNA (transfer RNA)
• mRNA


  Carries the genetic message from DNA to the ribosome
• rRNA


  Major component of ribosomes, where proteins are synthesized
• tRNA


  Transfers amino acids to match the mRNA codon