12-1: DNA Biology 2

In the mid 1900’s biologists wondered: How do genes work? What are they made of? How do they determine characteristics? Are they single molecules? Introduction

Biologists needed to discover the chemical nature of genes If they could figure out how genes carried genetic information, could understand how genes control characteristics of living things Introduction

1928: Frederick Griffith was trying to figure out what type of pneumonia made people sick Found 2 different types: smooth and rough – Smooth was deadly; Rough was not Gave mice shots with different types – Smooth (alone) killed mice – Rough (alone) did not kill mice – Smooth and Rough together killed mice Griffith and Transformation

Figured out that rough was transformed into smooth when together TRANSFORMATION: process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria Griffith discovered that the ability to cause disease was inherited by a gene Griffith and Transformation

1944: Oswald Avery wanted to repeat Griffith’s experiment Created a “juice” from heat- killed bacteria Used enzyme that would destroy DNA Transformation did not happen! Avery discovered that DNA stores/transmits genetic info Avery and DNA

1952: Alfred Hersey and Martha Chase were interested in which part of a virus could infect cells Used bacteriophages for experiment to study infection BACTERIOPHAGE: virus that infects bacteria Used radioactive markers on outside protein coat and DNA Discovered genetic material of bateriophage was DNA (not outside protein coat) Hersey- Chase Experiment

DNA had to be able to: 1.Genes had to carry information to next generation 2.Had to determine characteristics that can be inherited 3.Be easy to copy each time cell divides Components and Structure of DNA

DNA is made of building blocks called nucleotides NUCLEOTIDES: monomer of nucleic acids made up of a 5- carbon sugar, a phosphate group, and a nitrogenous base Can have 4 different types of base: – Adenine – Guanine – Thymine – Cytosine Components and Structure of DNA

Backbone of DNA is sugar and phosphate groups FORM THE OUTSIDE OF THE “LADDER” Bases bond together to connect inside FORM THE INSIDE (STEPS) OF THE LADDER Components and Structure of DNA

PHOSPHATE SUGAR BASE

Shape of DNA is called “Double Helix” – Looks like a twisted ladder! Discovered by Francis Crick and James Watson in 1953 Chargaff’s Rule says that base pairs will always have equal numbers – Adenine = Thymine – Cytosine = Guanine Components and Structure of DNA

Section Assessment 1.___________: process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria 2.DNA can have 4 different types of bases: ___________, ___________, ___________, ___________ 3.Shape of DNA is called “___________” 4.Chargaff’s Rule says that ___________ will always have ___________