Ch 5 B

• Semi-conservative replication


  Synthesis of new DNA where each parent DNA molecule is used as a template to synthesize a new strand of complementary DNA

  
• DNA replication


  1. Hydrogen bonds between bases of the parent DNA molecule break

  2. Each parent molecule is used as a template to synthesize a new strand of complementary DNA

  
• DNA replication


  • It is semi-conservative
  • Each daughter helix is composed of one strand of parental DNA and one strand of newly synthesized DNA

  
• Origin of replication (ori)


  • Specific sequence where replication begins
  • DNA helix separates (unwinds) to produce two single-stranded templates

  
• DNA polymerase


  • Catalyzes synthesis of new strand of DNA
  • Adds new nucleotides at the 3'-end of the growing DNA molecule
  • Uses complementary base pairing to select new nucleotide
  • Catalyzes formation of new phosphodiester bonds
  • Energy for synthesis comes from hydrolysis of triphosphate group of incoming nucleotide

  
• DNA helicase


  • Unwinds DNA double helix
  • Exposes more single-stranded template

  
• Central Dogma


  • A description of information flow in the cell
  • How information in DNA is decoded
• Transcription


  Synthesis of RNA using DNA as a template

  
• Translation


  Synthesis of a polypeptide using the information encoded in mRNA

  
• Transcription occurs one gene at a time
• Gene


  • A unit of hereditary information consisting of a specific sequence of nucleotides in DNA
  • Each gene has a unique sequence
  • All genes can be transcribed to produce RNA
  • Many (but not all!) genes encode proteins

  
• Gene expression


  The process by which DNA directs the synthesis of proteins

  
• Transcription


  1. Two strands of parental DNA separate by breaking H-bonds

  2. Single-stranded DNA acts as a template to create complementary strand of RNA

  3. Uses complementary base-pairing rules

  
• RNA polymerase (RNAP)


  • Incorporates new RNA nucleotides onto the 3' end of a growing RNA molecule
  • Forms phosphodiester bonds
  • Requires a single-stranded DNA template
  • Follows base-pairing rules

  
• Promoter


  Specific sequence of DNA where RNAP binds and begins transcription

  
• Terminator


  Specific sequence of DNA where RNA polymerase falls off template and ends transcription

  
• Template strand


  • The strand of DNA that is used as the template for RNA synthesis
  • RNA is synthesized by complementary base pairing

  
• Non-template strand (coding strand)


  Has the same sequence as the RNA produced

  
• Types of RNA produced by transcription

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

  
• Transcription


  1. RNA polymerase binds promoter

  2. Uses template strand of DNA to synthesize RNA

  3. Dissociates from template at terminator

  
• Template strand


  Only one strand of DNA is the template
• Non-template strand (coding strand)

  Has same sequence as RNA produced

  
• RNAs produced by transcription

  • mRNA: Carries information for translation, translated into proteins
  • rRNA: Structural and enzymatic component of the ribosome
  • tRNA: Guides amino acids to the ribosome during translation

  
• pre-mRNA


  The initial RNA transcript before modifications have been made

  
• Mature mRNA


  An RNA transcript that has been modified

  
• 5' Cap


  • Modified guanine (G) nucleotide added to 5' end
  • Protects mRNA from degradation
  • Aids in attachment to ribosome

  
• 3' Poly-A tail


  • 50-250 adenine (A) nucleotides added to 3' end
  • Protects RNA from degradation
  • Aids in export from nucleus to cytoplasm

  
• Introns


  Non-coding or intervening sequences
• Exons


  Coding or expressed sequences
• mRNA splicing


  1. Spliceosome enzyme cuts out introns from pre-mRNA, and joins together exons

  2. Produces mature mRNA with continuous protein coding sequence

  
• Codon


  A three-nucleotide sequence of RNA that specifies a particular amino acid

  
• Reading Frame


  • The way a cell's translation machinery groups the mRNA nucleotides into codons
  • Codons do not overlap
  • 3 possible frames per sequence, but only one makes sense

  
• 61 of 64 codons encode amino acids
• Start codon (AUG)


  • Tells ribosome where to start translation
  • Defines reading frame
  • Encodes a methionine (met) amino acid
  • All proteins start with Met

  
• Stop codons


  • Do not encode amino acids
  • Tells ribosome where to stop translation

  
• 5' untranslated region (UTR)


  Before start codon, not translated, involved in ribosome binding

  
• Open reading frame (ORF)

  Encodes the protein, no stop codons present

  
• 3' untranslated region (UTR)

  After stop codon, not translated
• The genetic code is universal, same in all organisms
• Genes can be moved between organisms