the history of dna
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The History of DNA. Honors Biology Chapter 12 Section 1. Griffith. 1928 Fredrick Griffith studying how bacteria made people sick and how different types of bacteria caused pneumonia - PowerPoint PPT PresentationTRANSCRIPT
The History of DNAHonors Biology
Chapter 12 Section 1
1928 Fredrick Griffith studying how bacteria made people sick and how different types of bacteria caused pneumonia
Isolates 2 strains (types) of bacteria from mice. Disease causing (grows in smooth colonies) and non-disease causing (grows in rough colonies)
Injects mice with disease causing: mice get pneumonia and die
Injects mice with non-disease causing: mice survive
Griffith
Griffith wonders if disease causing bacteria produce a toxic poison???
Griffith takes disease causing bacteria and heats it to kill the bacteria. Injects the heat killed bacteria into mice: mice survive
Griffith mixes heat killed bacteria with the non-disease causing bacteria injects into mice: mice get pneumonia and die
Griffith
Somehow the heat killed bacteria had passed their disease causing ability to the harmless strain
Griffith called this process transformation because the non-disease causing bacteria had been changed to disease causing
Griffith hypothesized that when the 2 strains were mixed, one factor was transferred from one strain of bacteria to the other. That factor had the ability to be passed from 1 generation to the next, transforming factor might be a gene
Griffith
Video of Griffith Experiment
Chapter 12A.mpg
Griffith
1944 Scientists wanted to know which molecule of the heat killed bacteria was required for the transformation
Took an extract from the heat killed bacteria and added enzymes that destroyed proteins, transformation still occurred
Repeated procedures for lipids, carbs and RNA, transformation still occurred
Repeated procedures for DNA, transformation did not occur
Avery
CONCLUSION: DNA was the transmitting factor
Concluded that the nucleic acid DNA stores and transmits the genetic information from 1 generation to the next
Avery
1952 Studied viruses, non-living particles that infect living organisms. Studied bacteriophage which means “bacteria eater”. Consists of a DNA or RNA core and a protein coat.
When bacteriophage infects a bacterium, the virus attaches, injects it’s genetic info. The viral genes produce many bacteriophages until they destroy the bacterium. The cell splits open and 100’s of bacteriophages burst out
Hershey and Chase
Bacteriophage
Reasoned that if they could determine which part of the virus (protein coat or genetic info) infected the cell, they could determine whether genes were made from DNA or protein
Used isotopes of phosphorus 32 and sulfur 35
protein does not contain phosphorusDNA and RNA does not contain sulfur
Radioactive isotopes used as markers
Hershey and Chase
DNA and RNA marked with phosphorus Protein marked with sulfur Mixed viruses with the bacteria for
radioactivity All of the radioactivity in the bacteria was
from phosphorus 32 the marker found in DNA
Conclusion: the genetic material of the bacteriophage was DNA and not the protein coat
Hershey and Chase
Hershey and Chase
DNA is a long molecule made of units called nucleotides
Each nucleotide made of a 5 carbon sugar called deoxyribose, a phosphate group and a nitrogen base. Hence DNA stands for Deoxyribonucleic acid
There are 4 nitrogen bases: adenine, guanine, thymine and cytosine
Adenine and guanine belong to a group called the purines whose structure contains 2 rings
Cytosine and thymine belong to a group called the pyrimidines whose structure contains 1 ring
Components and Structure of DNA
The backbone of a DNA chain is made of the deoxyribose sugars and phosphate groups of each nucleotide
The nucleotides may be joined in any sequence
Although there is only 4, many combinations are possible (alphabet analogy)
Components and Structure of DNA
DNA Nucleotides
Discovered the following, known as chargaff’s rule
amount of cytosine (c) = amount of guanine (g)
amount of adenine (a) = amount of thymine (t)
Chargaff’s Rules
1952 used an xray beam to help determine structure of DNA. The xrays diffracted on film providing specific patterns for the shape of DNA
The x shaped pattern Suggested DNA was a double
helix, double stranded and nitrogen bases were at center of molecule
Died at age 37 from cancer
Rosalind Franklin
1953 James Watson and Francis Crick developed a 3D model of DNA from cardboard and wire
Watson shown a pic of Franklin’s x-ray “my mouth fell open and my pulse began to race”
Model was a double helix – 2 strands wound around each other
Later discovered that the forces that held the nitrogen bases together were hydrogen bonds
Hydrogen bonds can only form between certain base pairs, A and T & C and G
Came up with the idea of base pairing which explained chargaff’s rule: A bonds with T and C bonds with G
Watson and Crick
Watson and Crick
DNA Structure
Create a time line of the scientific findings that led us to the discovery of the structure and function of DNA
BE CREATIVE!!!!!!!
Due tomorrow
Assignment