BIOSC 0100 Lecture Notes - Lecture 5: Maurice Wilkins, X-Ray Crystallography, Francis Crick

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6 Feb 2017

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Chapter 4
Three types of biological polymers:
-Proteins (monomer = amino acids)
-Nucleic Acids (monomer = nucleotide)
-Complex Carbohydrates (monomer = simple sugar)
Structure of Nucleotides
-Composed of a phosphate group, a five-carbon sugar, and a nitrogenous base
-Sugar in RNA is ribose (two OH) and in DNA it is deoxyribose (one OH)
-Deoriose is issig a hdrol group o the ’
-The phosphate group attahes at the 5’ ad the itrogeous ase attahes at the ’
-5’ phosphate ad ’ hdrol uliked
-Primary: sequence of nucleotides on the sugar-phosphate backbone
Nitrogenous Bases:
-Pyrimidines 6 atom ring structure with C and N in ring
-Cytosine, Urasil (RNA), Thymine (DNA) [must know structure] CuTie Pye
-Purines 9 atom ring structure with C and N in the ring
-Guanine, Adenine [must know structure] Pure As Gold
-Same as amino acids condensation reactions (monomer in, water out)
-Nucleotide polerizatio fors phosphodiester ods likages etee the ’ C hdrol o
oe uleotide ad the 5’C phosphate of the et uleotide
-The eerg for polerizatio oes fro uleoside triphosphates atiated uleotides
-Polymer of deoxyribonucleotides
-Bases-A, G, C, and T
-Deoxyribose sugar
Eri Chargraff’s Rules:
-Number of purines in any DNA sample is equal to the number of pyrimidines
-Number of adenine is equal to number of thymine
-Number of cytosine is equal to the amount of guanine
Rosland Franklin & Maurice Wilkins
-Used x-ray crystallography to determine that DNA had a repeating, helical shape
-Suggested that phosphate backbone was on the outside of the helix
Francis Crick & James Watson
-Built a physical odel of DNA to attept to reoile Chargraff’s rules ad the -rays
-Determined that there were two strands of DNA in the helix and they were antiparallel
-Oe strad 5’-’ d the other ra i ’-5’
-The hydrophilic sugar-phosphate backbone faces the exterior (hydrophilic because phosphates
are negatively charged)
-Nitrogenous base pairs face the interior
-Hydrophobic and van der Waals interactions help stabilize the interior (stacking of base pairs)
-The strands are stabilized by hydrogen bonds between complementary pairs
-GC has 3 hydrogen bonds while AT has 2 hydrogen bonds (GC is more stable)
-As it twists around the distance between backbones varies
-DNA can store and transmit biological information growth and reproduction of all cells
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