Biochemistry of the Genome

What did most scientists in the 1900 believe was what stored genetic information? 

• proteins 

Griffith

• discovery of transformation in bacteria

Hershey-Chase

• DNA is the genetic material

Avery-MacLaod-McCarty

• DNA can pass traits between organisms

What gives colonies smooth or rough appearance?

• the presence or absense of the capsule 

Griffith Experiment

• Streptococcus pneumonia

  • R: non-virulent 

  • S: virulent 

• Mice were infected with:

  • R: survival

  • S: death 

  • heat killed S: survival

  • R + heat killed S: death 

What was the conclusion of Griffith experiment? 

• a chemical factor from the virulent strain transforms the nonvirulent strain 

Avery-Macleoid- McCarthy Experiment (1944)

• evidence for DNA as genetic material

• Streptococcus pneumonia

  • R: non-virulent 

  • S: virulent 

• treat heat killed cells with enzymes to break down DNA, RNA, or protein

• then test transformation 

Results of Avery-Macleoid- McCarthy Experiment

• DNA+RNA+Protein → transformation

• DNA+RNA → transformation 

• DNA+ Protein → transformation 

• RNA +Protein → no transformation

• first clear evidence that genetic molecule is DNA  

S radioactivity (protein)

• remains with detached phage 

P radioactivity (DNA)

• transferred to bacteria 

• DNA must be the storage molecule

use of E.coli and phage T2 as model system

• phage have only protein and DNA

  • only DNA contains P

  • only Protein contains S 

Prepared batches pf phage with either

• DNA labeled with P

• Protein Labeled with S 

allowed phage to infect bacteria

• used a blender to detach phage 

• used centrifuge to separate phage from ecoli to determine which was radioactive

DNA structure

• double helix structure

• negative charged phosphodiester backbone

• major and minor groves between strands

Phosphodiester Bond

• links phosphate to ribose 3 on carbon

• forms phosphodiester backbone 

Nucleic Acids

• directional 

• 5’ C at one end 

• 3’ C at the other end

• written 5’ → 3’

Nucleotide characteristics

• relatively hydrophobic 

• polar groups

• high density of negative charge 

DNA Base Pairing 

• forms due to hydrogen bonding patterns 

  • A-T

  • G-C

• allows nucleic acid strands to hybridize 

• strands run antiparallel 

Where can protein interact with DNA and interact with the nucleotide sequence

• major groove

Important facts about DNA

• basic structure is nucleotides

• hydrogen bonds stabilize base pairing 

• complementary strands 

RNA

• bases are A,G, C, and U (uracil)

• has ribose sugar 

• single stranded

ribonucleotide examples

• ATP

• GTP

What are the three types of RNA

• messenger RNA

• Ribosomal RNA

• transfer RNA 

What stabilizes RNA

• short areas of complementary base pairing

Features of RNA

• can fold upon itself

• can form complex 3D structures

• folded RNA can work as catalysis (ribozymes)

Flow of information in the cell

DNA → RNA → Protein

mRNA

• instructions for protein synthesis are transcribed into this 

tRNA

• involved in translation 

rRNA

• mRNA is translated into a protein and read by the ribosomes

What are the functions of RNA

• mRNA read by ribosomes

• tRNA helps read mRNA and deliver amino acids to polypeptide 

• ribosome mass is mostly rRNA 

Structure of RNA

• mRNA

  • unstructured

• rRNA and tRNA

  • structure circulate to their function