Lecture 6

• Genetic Code


  A typical protein is made up of one or more polypeptide chain which functions as enzymes that participate in metabolic process such as amino acid biosynthesis.
• A DNA

  Right handed helix with 11 base pairs per turn, Moderately dehydrated B Form
• B DNA


  Right handed helix with 10 residues per turn
• Z DNA


  Left handed helix with 12 base pairs per turn, Found in areas of alternating purines and pyrimidines
• Chargaff's Rule


  ADENINE will be paired with THYMINE by 2 hydrogen bonds,

  CYTOSINE will be paired by GUANINE by 3 hydrogen bonds
• Genetic code


  Genes specify proteins by means of genetic code,

  Refers to the instructions contained in a gene that can tell a cell how to make a specific protein
• Genetic code


  Each gene code uses the four nucleotide bases: adenine (A), Thymine (T), Cytosine (C), Guanine (G) in many ways in order to spell out 3-letter codons that specify which amino acid is needed at each position within a protein
• Codon


  consist of 3 bases
• there are total of _ codons

  64
• codons that code for amino acids

  61
• 3 stop codons that terminate translations


  UAG, UAA, UGA
• start of initiating codon _ for _ in eukaryotes or _ in prokaryotes


  UAG, Methionine, Formylmethionine
• Degenerate


  multiple codons may code for the same amino acid
• A specific codon always codes for the same amino acid

  Unambiguous
• the codons are read in continuing sequence of nucleotide triplets until translations stop codon is reached


  non-overlapping
• it has been conserved in very early stages of evolution with only slight differences in the manner in which the code translated


  Universal
• Central Dogma


  DNA -> RNA -> Protein
• Main function is to transfer genetic information from parent to progeny


  DNA replication
• Occurs during S phase of the cell cycle

  DNA replication
• Each strand serves as a template for complementary daughter strand

  Semi conservative process
• Each strand becomes part of the daughter strand

  Semi-conservative process
• DNA polymerase


  key enzymes
• DNA polymerase


  2 identical double stranded DNA
• the origin of replication (ori) is recognized by a group of proteins


  origin recognition complex (ORC)
• Helicase


  Unwinds the double helix, in the process that is driven by ATP
• DnaB


  is the principal helicase in E.Coli
• Single-stranded DNA-Binding proteins


  maintain the separation of the parent strands
• Topoisomerase


  relieve torsional strain the results from helicase-induced unwinding
• type (1)


  Swivelase
• type (2)


  Gyrase, inhibited by fluoroquinolones
• primase


  synthesis short segments of complementary RNA primers
• DNA polymerase3


  Elongates the DNA strand by adding new deoxyribonucleotides
• DNA polymerase 1


  removes the ribonucleotides using 5'-3' exonuclease
• DNA polymerase 1


  fills in the gaps with deoxyribonucleotides
• DNA ligase


  seals the nick by catalyzing the formation of the last phosphodiester bond, requiring hydrolysis of ATP
• Transcription


  Synthesis of RNA using DNA as a template
• Enhancers


  Are DNA sequences that stimulate transcription rate
• Silencers


  Inhibits transcriptions
• post-transcriptional modification


  A primary RNA transcript has introns and exons
• Introns


  non coding regions