unit 1

• Nucleotides

  Made up of a phosphate molecule, a sugar molecule (deoxyribose), and a base molecule
• DNA structure

  • Double-stranded helix
  • Nucleotides run in opposite directions (anti-parallel)
  • Bases (A, T, C, G) form complementary base pairs held together by hydrogen bonds
• Sugar-phosphate backbone

  Phosphate and sugar molecules are joined together by stronger sugar-phosphate bonds
• Deoxyribose sugar

  Contains 5 carbon molecules
• 5' end

  Has a phosphate group
• 3' end


  Where new nucleotides are added
• Prokaryotes

  • No membrane-bound organelles
  • Have a single circular chromosome
  • May have smaller circular plasmids
• Eukaryotes

  • Have membrane-bound organelles including a nucleus
  • Have linear chromosomes
  • Also have circular chromosomes in organelles like mitochondria and chloroplasts
• Yeast is a special example of a fungal cell that contains plasmids, even though it is a eukaryote
• Linear chromosomes in eukaryotes

  • DNA is very tightly coiled and packaged into histone proteins
• DNA replication

  The process by which DNA makes an exact copy of itself
• Steps of DNA replication

  1. DNA Helicase unwind DNA double helix

  2. Primer is added to 3’ end.

  3. New complementary bases are added to each strand following base rules.

  4. Two new DNA strands are formed
• Leading strand

  • DNA is added continuously to the 3' end
  • Replication proceeds in a continuous 'zipper-like' fashion
• Lagging strand

  • DNA is added in fragments to the 5' end
  • Replication is discontinuous
• Primers

  Short complementary sequences of nucleotides blinded to the 3’ end to provide a starting point for DNA polymerase to initiate replication
• DNA polymerase

  Enzyme that adds complementary nucleotides to form new DNA strands
• Ligase

  Enzyme that joins DNA fragments together on the lagging strand
• Requirements for DNA replication


  • Original DNA template
  • Free DNA nucleotides
  • Primers
  • DNA polymerase
  • Ligase
  • ATP
• Polymerase Chain Reaction (PCR)

  A technique used to amplify or make many copies of a specific DNA sequence in a laboratory setting
• Steps of PCR

  1. Heat DNA sample to 94 degrees to break the weak hydrogen bonds between bases to separate strands.

  2. Cool DNA sample to 55 degrees to allow the primers to bond to their specific target sequences on DNA.

  3. Heat DNA sample again to 72 degrees to allow the TAQ Polymerase to add nucleotides to the 3’ ends.
• Thermal cycler

  • Machine that cycles through different temperatures to automate the PCR process
• Uses of PCR

  • Forensics
  • Paternity testing
  • Medical diagnosis
• Requirements for PCR

  • Original DNA template
  • Primers
  • DNA nucleotides
  • pH buffer
  • Heat-resistant DNA polymerase
  • Thermal cycler
• Gene expression

  The process of using information from a gene in order to synthesize or make a protein
• Genotype


  The sequence of bases and genes that an organism has
• Phenotype

  What an organism physically looks like, determined by the proteins that are synthesised when genes are expressed
• Protein synthesis

  DNA -> mRNA -> Ribosome -> Amino acids -> Protein
• Transcription

  The synthesis of an mRNA strand from a section of DNA
• Translation

  The synthesis of a protein using the genetic instructions from mRNA at the ribosome
• RNA

  • Single-stranded
  • Uses ribose sugar
  • Adenine pairs with uracil
• mRNA

  A copy of the genetic code from the nucleus to the ribosome
• tRNA

  Carries a specific amino acid to the ribosome
• rRNA

  Part of the ribosome, made up of proteins and RNA
• Transcription

  1. DNA unwinds

  2. RNA polymerase synthesizes mRNA strand

  3. Stop codon reached
• Codon

  A triplet of bases on mRNA that codes for a specific amino acid
• Splicing

  1. Introns removed

  2. Exons joined together to form mature mRNA
• The same gene can produce multiple mature mRNA transcripts and different proteins due to alternative RNA splicing
• Translation

  1. mRNA attaches to ribosome

  2. tRNA brings amino acids to match codons

  3. Peptide bonds form between amino acids

  4. Protein folding
• The shape of a protein determines its function
• Alternative RNA Splicing

  Creates a range of different proteins from the same gene by varying the combination of exons