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Lecture 28

BIOL 1000 Lecture 28: Biology Lecture 28

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Biological Sciences
BIOL 1000
Kevin G.Scott

Biology Lecture 28: Identification of molecules of inheritance loomed as a major challenge to biologists in the early 20 century. In DNA phosphate units join one sugar to the other sugar. There is a directionality in DNA coming from the sugars and how they are attached. *Carbons 3 and 5 are what are attached to the phosphates. The sugar is attached to its own sugar on the 5 prime end, and is attached to another sugar via 3 prime carbon. Hydrogen bonds join the 4 nitrogenous bases in DNA Maurice Wilkens and Rosalind Franklin were using a technique called xray crystallography to study molecular structure Produced a picture of the dna molecule using this technique, key to work Watson and Crick did. When she shot x rays through the molecule, it suggested that DNA was possibly a helical structure. Xray crystallographic images of Dna enabled Watson to deduce that dna was helical and the width of the helix and the spacing of the nitrogenous basis The width suggested that the dna molecule was made up of 2 strands forming a double helix* *Chargaffs rules state that in any species there is an equal number of A and T bases, and an equal number of C and G bases 2 antiparallel sugar back bones one running 5 prime to 3 prime and the other running from 3 prime to 5 prime. Picture a ladder, hydrogen bonds are middle parts, sugars outer. A pairs with T and C pairs with G as you already know In the Watson Crick model in any organism the amount of A Equals T and the amount of C equals G. It explains chargaffs rule *Guanine and Adenine have 2 rings, Thymine and Cystosine have only 1 ring. Adenine binds with thymine because one has one ring the other has 2, and they can bind at specific points When DNA is about to be replicated it opens up, unzips the bases become exposed. DNA is replicated by adding in a new series of DNA where new nitrogenous bases are added to get the code from the dna. 2 single strands of dna are made from the parent strand, this is just the basic process of it. Since the two strands of dna are complementary each initial strand acts as a template for building a new strand in replication
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