12–1 dna

12–1 DNA12–1 DNA

Griffith and TransformationGriffith and Transformation Griffith and TransformationGriffith and Transformation

» In 1928, British scientist Fredrick Griffith was trying to In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia.learn how certain types of bacteria caused pneumonia.

» He isolated two different strains of pneumonia bacteria He isolated two different strains of pneumonia bacteria from mice and grew them in his lab.from mice and grew them in his lab.

Griffith and TransformationGriffith and Transformation

» Griffith made two observations:Griffith made two observations:» (1) The disease-causing strain of bacteria grew into (1) The disease-causing strain of bacteria grew into

smooth colonies on culture plates. smooth colonies on culture plates. » (2) The harmless strain grew into colonies with (2) The harmless strain grew into colonies with

rough edges.rough edges.


– Griffith's Griffith's ExperimentsExperiments

» Griffith set up four Griffith set up four individual individual experiments. experiments.

» Experiment 1: Mice Experiment 1: Mice were injected with were injected with the disease-causing the disease-causing strain of bacteria. strain of bacteria. The mice developed The mice developed pneumonia and pneumonia and died.died.


Experiment 2: Mice Experiment 2: Mice were injected with were injected with the harmless strain the harmless strain of bacteria. These of bacteria. These mice didn’t get sick.mice didn’t get sick.


Experiment 3: Experiment 3: Griffith heated the Griffith heated the disease-causing disease-causing bacteria. He then bacteria. He then injected the heat-injected the heat-killed bacteria into killed bacteria into the mice. The mice the mice. The mice survived.survived.

Griffith and TransformationGriffith and Transformation» Experiment 4: Experiment 4:

Griffith mixed Griffith mixed his heat-killed, his heat-killed, disease-causing disease-causing bacteria with bacteria with live, harmless live, harmless bacteria and bacteria and injected the injected the mixture into the mixture into the mice. The mice mice. The mice developed developed pneumonia and pneumonia and died.died.

Griffith and TransformationGriffith and Transformation»Griffith Griffith

concluded that concluded that the heat-killed the heat-killed bacteria passed bacteria passed their disease-their disease-causing ability causing ability to the harmless to the harmless strain.strain.

Griffith and TransformationGriffith and Transformation– Transformation Transformation

» Griffith called this process Griffith called this process transformationtransformation because one strain of bacteria (the harmless strain) because one strain of bacteria (the harmless strain) had changed permanently into another (the had changed permanently into another (the disease-causing strain). disease-causing strain).

» Griffith hypothesized that a factor must contain Griffith hypothesized that a factor must contain information that could change harmless bacteria information that could change harmless bacteria into disease-causing ones.into disease-causing ones.

Avery and DNAAvery and DNA

Avery and DNAAvery and DNA» Oswald Avery repeated Griffith’s work to determine Oswald Avery repeated Griffith’s work to determine

which molecule was most important for which molecule was most important for transformation.transformation.

» Avery and his colleagues made an extract from the Avery and his colleagues made an extract from the heat-killed bacteria that they treated with enzymes.heat-killed bacteria that they treated with enzymes.


The enzymes destroyed proteins, lipids, The enzymes destroyed proteins, lipids, carbohydrates, and other molecules, carbohydrates, and other molecules, including the nucleic acid RNA.including the nucleic acid RNA.

Transformation still occurred.Transformation still occurred.


Avery and other scientists repeated the Avery and other scientists repeated the experiment using enzymes that would break experiment using enzymes that would break down DNA.down DNA.

When DNA was destroyed, transformation When DNA was destroyed, transformation did not occur. Therefore, they concluded did not occur. Therefore, they concluded that DNA was the transforming factor.that DNA was the transforming factor.


– What did scientists discover about the What did scientists discover about the relationship between genes and DNA?relationship between genes and DNA?

Avery and DNAAvery and DNA– Avery and other scientists discovered that the Avery and other scientists discovered that the

nucleic acid DNA stores and transmits the genetic nucleic acid DNA stores and transmits the genetic information from one generation of an organism to information from one generation of an organism to the next.the next.

The Hershey-Chase ExperimentThe Hershey-Chase Experiment

The Hershey-Chase ExperimentThe Hershey-Chase Experiment» Alfred Hershey and Martha Chase studied Alfred Hershey and Martha Chase studied

viruses—nonliving particles smaller than a viruses—nonliving particles smaller than a cell that can infect living organisms.cell that can infect living organisms.


– Bacteriophages Bacteriophages » A virus that infects bacteria is known as a A virus that infects bacteria is known as a

bacteriophage.bacteriophage. » Bacteriophages are composed of a DNA or Bacteriophages are composed of a DNA or

RNA core and a protein coat.RNA core and a protein coat.


» When a bacteriophage enters a bacterium, When a bacteriophage enters a bacterium, the virus attaches to the surface of the cell the virus attaches to the surface of the cell and injects its genetic information into it. and injects its genetic information into it.

» The viral genes produce many new The viral genes produce many new bacteriophages, which eventually destroy the bacteriophages, which eventually destroy the bacterium. bacterium.

» When the cell splits open, hundreds of new When the cell splits open, hundreds of new viruses burst out.viruses burst out.


» If Hershey and Chase could determine which If Hershey and Chase could determine which part of the virus entered an infected cell, they part of the virus entered an infected cell, they would learn whether genes were made of would learn whether genes were made of protein or DNA.protein or DNA.

» They grew viruses in cultures containing They grew viruses in cultures containing radioactive isotopes of phosphorus-32 (radioactive isotopes of phosphorus-32 (3232P) P) and sulfur-35 (and sulfur-35 (3535S).S).


If If 3535S was found in the bacteria, it would S was found in the bacteria, it would mean that the viruses’ protein had been mean that the viruses’ protein had been injected into the bacteria.injected into the bacteria.


If If 3232P was found in the bacteria, then it was P was found in the bacteria, then it was the DNA that had been injected.the DNA that had been injected.

The Hershey-Chase ExperimentThe Hershey-Chase Experiment– Nearly all the radioactivity in the bacteria was Nearly all the radioactivity in the bacteria was

from phosphorus (from phosphorus (3232P).P).– Hershey and Chase concluded that the genetic Hershey and Chase concluded that the genetic

material of the bacteriophage was DNA, not material of the bacteriophage was DNA, not protein.protein.

The Components and Structure of The Components and Structure of DNADNA

– What is the overall structure of the DNA What is the overall structure of the DNA molecule?molecule?

The Components and Structure The Components and Structure of DNAof DNA

The Components and Structure of DNAThe Components and Structure of DNA» DNA is made up of DNA is made up of nucleotidesnucleotides. . » A nucleotide is a monomer of nucleic acids made up A nucleotide is a monomer of nucleic acids made up

of a five-carbon sugar called deoxyribose, a of a five-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base.phosphate group, and a nitrogenous base.

The Components and The Components and Structure of DNAStructure of DNA

There are There are four kinds of four kinds of bases in in bases in in DNA:DNA:

» adenineadenine» guanine guanine » cytosinecytosine» thyminethymine


The backbone of a DNA chain is formed by The backbone of a DNA chain is formed by sugar and phosphate groups of each sugar and phosphate groups of each nucleotide. nucleotide.

The nucleotides can be joined together in The nucleotides can be joined together in any order.any order.


– Chargaff's RulesChargaff's Rules» Erwin Chargaff discovered that:Erwin Chargaff discovered that:

The percentages of guanine [G] and The percentages of guanine [G] and cytosine [C] bases are almost equal in any cytosine [C] bases are almost equal in any sample of DNA. sample of DNA.

The percentages of adenine [A] and The percentages of adenine [A] and thymine [T] bases are almost equal in any thymine [T] bases are almost equal in any sample of DNA.sample of DNA.


– X-Ray Evidence X-Ray Evidence » Rosalind Franklin used X-Rosalind Franklin used X-

ray diffraction to get ray diffraction to get information about the information about the structure of DNA.structure of DNA.

» She aimed an X-ray beam at She aimed an X-ray beam at concentrated DNA samples concentrated DNA samples and recorded the scattering and recorded the scattering pattern of the X-rays on pattern of the X-rays on film.film.


The Double Helix The Double Helix – Using clues from Franklin’s pattern, James Watson Using clues from Franklin’s pattern, James Watson

and Francis Crick built a model that explained how and Francis Crick built a model that explained how DNA carried information and could be copied.DNA carried information and could be copied.

– Watson and Crick's model of DNA was a double helix, Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other.in which two strands were wound around each other.

The Components and Structure of DNA


Watson and Crick discovered that hydrogen Watson and Crick discovered that hydrogen bonds can form only between certain base bonds can form only between certain base pairs—adenine and thymine, and guanine pairs—adenine and thymine, and guanine and cytosine. and cytosine.

This principle is called This principle is called base pairingbase pairing..

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Review QuizReview Quiz

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– Avery and other scientists discovered that Avery and other scientists discovered that » DNA is found in a protein coat.DNA is found in a protein coat.» DNA stores and transmits genetic information from DNA stores and transmits genetic information from

one generation to the next.one generation to the next.» transformation does not affect bacteria.transformation does not affect bacteria.» proteins transmit genetic information from one proteins transmit genetic information from one

generation to the next.generation to the next.

12–112–1– The Hershey-Chase experiment was based on the The Hershey-Chase experiment was based on the

fact thatfact that» DNA has both sulfur and phosphorus in its structure.DNA has both sulfur and phosphorus in its structure.

» protein has both sulfur and phosphorus in its structure.protein has both sulfur and phosphorus in its structure.

» both DNA and protein have no phosphorus or sulfur in both DNA and protein have no phosphorus or sulfur in their structure.their structure.

» DNA has only phosphorus, while protein has only sulfur DNA has only phosphorus, while protein has only sulfur in its structure.in its structure.

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– DNA is a long molecule made of monomers DNA is a long molecule made of monomers called called

» nucleotides.nucleotides.» purines.purines.» pyrimidines.pyrimidines.» sugars.sugars.

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– Chargaff's rules state that the number of Chargaff's rules state that the number of guanine nucleotides must equal the number of guanine nucleotides must equal the number of

» cytosine nucleotides.cytosine nucleotides.» adenine nucleotides.adenine nucleotides.» thymine nucleotides.thymine nucleotides.» thymine plus adenine nucleotides.thymine plus adenine nucleotides.

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– In DNA, the following base pairs occur:In DNA, the following base pairs occur:» A with C, and G with T.A with C, and G with T.» A with T, and C with G.A with T, and C with G.» A with G, and C with T.A with G, and C with T.» A with T, and C with T.A with T, and C with T.

END OF SECTIONEND OF SECTION

12–1 dna

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