BIOLOGY CHAPTERS 16
• Experiments with bacteria and with phages provided the first strong evidence that the genetic
material is DNA.
o DNAis used by all living organisms (that carry out the characteristics of life)
• Watson and Crick deduced that DNAis a double helix and built a structural model. Two
antiparallel sugar-phosphate chains wind around the outside of the molecule; the nitrogenous
bases project into the interior, where they hydrogen-bond in specific pairs,Awith T, G with C.
o 1866- Gregor Mendel published the results of his investigations of the inheritance of
"factors" in pea plants.
o 1950's- Wilkins, Franklin, Crick, Watson discover chemical structure of DNA, starting a
new branch of science--molecular biology.
o Watson and Crick made a model of the DNAmolecule and proved that genes determine
o Showed how information is stored in molecule’s structure and how DNAmolecules are
templates for their own replication
o DNAis a polymer of nucleotides
o Each nucleotide subunit contains a nitrogenous base, pentose sugar, and phosphate group
o The order of the building blocks of DNAstore genetic information
o Base pairs
Hydrogen bonding- between specific pairs; binds two chains of helix
Hydrogen bonds are weak, allowing DNAto unzip easily A& T forms two bonds, G & C forms 3 bonds
• Backbone of DNAchain
o Alternating sugar and phosphate groups
o Joined by covalent bonds
o Double helix, chains run side by side, antiparallel, one is going one way, the other is
going the other way
o 5’end phosphate attatched o 5’deoxyribose carbon
o 3’end hydroxyl attatched to 3’deoxyribose carbon
• Semiconservative Replication
o Each daughter double helix consists of 1 original strand from parent and 1 new
• The Meselson-Stahl experiment showed that DNAreplication