central dogma

• DNA is replicated with each division cycle
• Semi-conservative: one parent strand conserved
• DNA is transcribed into mRNA
• Transcribe one form of nucleic acid into another form

  Same “language”: nucleic acid
• mRNA is translated into protein

  language of nucleic acid translated into language of amino acids
• Notable exceptions: viruses
• Central dogma: information never passed beginning with proteins
• Translation occurs on the ribosome, which contains rRNA and many other protein
• In translation, tRNA carries amino acids to the ribosome and binds to its complement in the mRNA template
• Amino acids are dictated by the Genetic Code
• Genetic Code

  • Triplet codons

  o 64 codons

  • 20 common amino acids

  • 3 stop codons
• Code is degenerate

  • More than one codon for most amino acids
  • Third base “wobble”
  • Except methionine: always the start codon
• Code – universal
• Transcription

  RNA synthesis proceeds by complementary base pairing with one of the DNA strands
• Transcription

  This strand acts as template to determine which ribonucleotide gets added and in what order
• Transcription

  The DNA strand that guides its synthesis is therefore the “noncoding” or template strand
• Transcription

  The mRNA synthesized contains the genetic code

  The complementary strand of DNA is therefore the coding strand

  The mRNA product is therefore an RNA copy of the coding strand of the DNA (U in place of T)
• Our understanding of biological molecules:

  • Increased in the 20th century

  • Discovered shared genetic code in all living organisms
• In 1956, Francis Crick proposed:

  • DNA as an informational storage molecule

  • Central Dogma of Molecular Biology:

  o DNA → RNA → Protein
• Transcription: • DNA → mRNA • mRNA is a genetic messaging molecule
• Translation:

  • mRNA → Protein

  • Ribosome reads mRNA, assembles amino acids

  • Proteins:

  o Cellular machinery

  o Specific three-dimensional shape

  o Determines function
• Transcription/translation to printing an essay
• DNA is stored data, mRNA is the message to the ribosome
• DNA and RNA:

  • Chemical language based on nucleotides

  • Transcription exchanges information in the same language
• Structure of DNA:

  • Double-stranded nucleic acid
  • Composed of deoxyribonucleotides
  • Four nitrogenous bases: A, T, C, G
• RNA:

  • Single-stranded nucleic acid

  • Composed of ribonucleotides

  • Four nitrogenous bases: A, U, C, G
• Nucleotides:

  • Form nucleic acids

  • Composed of phosphate group, sugar, nitrogenous base
• Phosphodiester Bond:

  • Covalent bond between nucleotides

  • Forms the backbone of nucleic acids
• DNA Secondary Structure:

  • Double helix

  • Chargaff's rule and base pairing
• Proteins:

  • Polymers of amino acids

  • 20 amino acids in living organisms

  • Sequence coded for by DNA
• Protein Structure:

  • Primary, secondary, tertiary, quaternary structure

  • Determines function

  • Altered function with changes in structure
• Sickle Cell Anemia:

  • Example of protein structure affecting function

  • Single amino acid change affects hemoglobin function
• Protein Folding:

  • Determined by interactions between R groups

  • Hydrogen bonds, ionic bonds, hydrophobic

  interactions
• Quaternary Structure:

  • Fully functional protein structure

  • Composed of multiple polypeptides
• Translation is the process by which mRNA codons are deciphered and a particular protein molecule is synthesized
• substances needed for the translation phase of protein synthesis are

  • mRNA molecules,
  • tRNA molecules,
  • amino acids,
  • ribosomes
• ribosome is an rRNA–protein complex that serves as the site for the translation phase of protein synthesis.
• The active site is mostly rRNA, with only one of the ribosome’s many protein components being present.
• rRNA is so predominant at the active site, the ribosome is thought to be an RNA enzyme (Section 21-1), that is, a ribozyme.
• mRNA involved in the translation phase of protein synthesis binds to the small subunit of the ribosome.