DNA SC STANDARD B-4: THE STUDENT WILL DEMONSTRATE AN UNDERSTANDING OF THE MOLECULAR BASIS OF GENETICS

Cornell Notes Topic: DNA EQ: How does the overall structure of DNA explain the mechanism of inheritance?

HistoryGriffith’s Experiment 1928: Griffith Transformation : ◦ Process by which 1 strain of bacteria is changed into a 2nd strain after being in the presence of the 2 nd strain

DNA Avery: 1944 ◦ Identified transforming agent as DNA

Hershey-Chase Experiment Bacteriophages infect bacteria and transfer their genetic material to the bacteria’s DNA. These experiments proved it was the genetic material not the protein that “transformed” the bacteria.

Parts of DNA DNA 1. 5-carbon sugar: deoxyribose 2. Phosphate group 3. Nitrogenous Base 1.Purines 1.Adenine 2.Guanine 2.Pyrimidines 1.Cytosine 2.Thymin e

Chargaff’s Rules In same sample of DNA: cytosine = guanine ◦ [ C ] = [ G ] adenine = thymine ◦ [ A ] = [ T ]

X-RAY EVIDENCE Rosalind Franklin studied DNA using x-ray diffraction The pattern on the left gave some important clues as to the structure of DNA ◦ shaped in a helix ◦ nitrogenous bases in center

THE DOUBLE HELIX Watson & Crick Built 3-D models trying to find a structure that explained everything they knew DNA could do When they saw Franklin’s x-rays the shape became clear to them

DNA Had to be able to do 3 things: 1. carry information from 1 generation to next 2. use the information to produce traits 3. be easily copied

THE DOUBLE HELIX

DOUBLE HELIX TWISTED LADDER WITH RUNGS OF LADDER MADE UP OF THE NITROGENOUS BASES HELD TOGETHER BY HYDROGEN BONDS

DOUBLE HELIX BASE PAIRING EXPLAINED CHARGAFF’S RULES SINCE ADENINE ALWAYS PAIRED WITH THYMINE & GUANINE ALWAYS PAIRED WITH CYTOSINE