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DNA Structure
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DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

Dec 14, 2015

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Page 1: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Structure

Page 2: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

Frederick Griffith

•In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia

•Griffith injected mice with disease-causing bacteria, the mice died of pneumonia

•Griffith injected mice with harmless bacteria, the mice didn’t get sick

•Griffith thought that the disease-causing bacteria might produce a poison

Page 3: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

Frederick Griffith

•Griffith mixed heat-killed disease-causing bacteria with harmless bacteria and injected the mixture into mice

•To his amazement, the mice developed bacteria and many died

•He found that the lungs of those mice who died were not filled with harmless bacteria, but of disease-causing bacteria

Page 4: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

Frederick Griffith

•The heat-killed bacteria had passed their disease-causing ability to the harmless strain

•Griffith coined this process transformation because one strain of bacteria had been changed into another

•Griffith hypothesized that when the two types of bacteria were mixed, some factor was transformed from the heat-killed cells into the live harmless bacteria

Page 5: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

Frederick Griffith• Griffith discovered that the ability to cause

disease was inherited by the transformed bacteria’s offspring, the transforming factor was a gene

Page 6: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

Oswald Avery

•In 1944, a group of scientists repeated Griffith’s work

•Avery and his colleagues made an extract from the heat killed bacteria and treated the extract with enzymes that destroyed proteins, carbohydrates, lipids, and other molecules

•Since transformation still occurred, these molecules were not responsible for the transformation

Page 7: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

Oswald Avery

•Avery and other scientists repeated the experiment, this time using enzymes that targeted DNA

•When they destroyed the nucleic acid DNA, transformation did not occur

•Avery and other scientists discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next

Page 8: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

The Hershey-Chase Experiment•In 1952, American scientists Alfred Hershey

and Martha Chase collaborated in studying viruses

•One type of virus that infects bacteria is known as a bacteriophage

•Bacteriophages are composed of a DNA or RNA core and a protein coat

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

Page 9: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.
Page 10: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

The Hershey-Chase Experiment

•Hershey and Chase reasoned that if they could determine which part of the virus entered the infected cell, they would learn whether genes were made of protein or DNA

•Viruses were grown in cultures containing radioactive isotopes of phosphorus-32 (32P) and sulfur-35 (32S)

•Proteins contain almost no phosphorus and DNA contains no sulfur

Page 11: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•The radioactive substances were used as markers

•If 32S was found in the bacteria, it would mean that the viruses’ bacteria had been injected into the bacteria

•If 32P was found in the bacteria, then it was the DNA that had been injected

The Hershey-Chase Experiment

Page 12: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.
Page 13: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•Marked viruses were mixed with bacteria, after a few minutes viruses injected their genetic material

•Viruses were separated were from bacteria, bacteria was tested for radioactivity

•Nearly all the radioactivity in the bacteria was from phosphorus, the marker found in DNA

•Hershey and Chase demonstrated that DNA, not protein, functions as the phage’s genetic material

The Hershey-Chase Experiment

Page 14: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

The Components and Structure of DNA•DNA is made up of nucleotides•Nucleotides are made up of three basic

components: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base

Page 15: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•There are four kinds of nitrogenous bases in DNA

•Adenine and Guanine are two nitrogenous bases that belong in a group of compounds known as purines

•Cytosine and Thymine are known as pyrimidines

•Purines have two rings in their structures, whereas pyrimidines have one ring

The Components and Structure of DNA

Page 16: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•Adenine, guanine, cytosine, and thymine are four kinds of _________ bases in DNA.

Nitrogenous

Page 17: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•The phosphate of one nucleotide is attached to the sugar of the next nucleotide in line

•The result is a “backbone” of alternating phosphates and sugars

The Components and Structure of DNA

Page 18: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•Erwin Chargaff discovered that the percentages of guanine and cytosine bases are almost equal in any sample of DNA

•The same thing is true for the other two nucleotides, adenine and thymine

•The observation that [A]=[T] and [G]=[C] became known as Chargaff’s rules

The Components and Structure of DNA

Page 19: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•According to Chargaff’s rules, the percentages of ______are equal to thymine and the percentages of ______ are equal to guanine in the DNA molecule.

The Components and Structure of DNA

adeninecytosine

Page 20: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•Describe the components and structure of a DNA nucleotide.

• DNA is made of nucleotides. Each nucleotide has three parts: a 5-carbon sugar, a phosphate group, and a nitrogenous base

• The four nitrogenous bases are adenine and guanine (purines), cytosine and thymine (pyrimidines).

Page 21: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

The Components and Structure of DNA•Francis Crick and James

Watson were trying to understand the structure of DNA by building 3 dimensional models of the molecule

•Watson was shown a copy of Rosalind Franklin’s X-ray pattern of DNA

Page 22: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•Using clues from Franklin’s pattern, Watson and Crick had built a structural model that explained the puzzle of how DNA could carry information, and how it could be copied

•Watson and Crick’s model of DNA was a double helix in which two strands were wound around each other

The Components and Structure of DNA

Page 23: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.
Page 24: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

•Explain how Chargaff’s rules helped Watson and Crick model DNA.

The Components and Structure of DNA

•The two stands of DNA are held together by hydrogen bonds between certain bases-A and T, and G and C-which explained Chargaff’s rules.

Page 25: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

The Double Helix

•The two strands are held together by hydrogen bonds between the nitrogenous bases, which are paired in the interior of the double helix

•Hydrogen bonds can form only between certain base pairs-adenine and thymine, and guanine and cytosine.

•Base pairing principle that bonds DNA can form only between adenine and thymine and between cytosine and guanine

Page 26: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA and Chromosomes

•Eukaryotic chromosomes contain both DNA and proteins, packed together to form chromatin

•Eukaryotic chromosomes contain DNA wrapped around proteins called histones (globular proteins that DNA tightly coils around to form chromosomes)

Page 27: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication•The parent molecule has two complimentary

strands of DNA•The first step in replication is separation of

the two DNA strands•Each parent strand now serves as a template

that determines the order of nucleotides along a new complementary strand

•Each parent stand produces two new complimentary strands following the rules of base pairing

Page 28: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•What is the complimentary strand of bases for a strand with the bases TACGTT?

ATGCAA

Page 29: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

Page 30: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•The replication of a DNA molecule begins at special sites called origins of replication

•Proteins recognize a stretch of DNA having a specific sequence of nucleotides

•These proteins attach to the DNA and separate the two strands and open up a replication “bubble”

Page 31: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•Once the two strands of the double helix have separated, two replication forks (a Y-shaped where the new strands of the DNA are elongating) form at the end of a replication “bubble”

•As each new strand forms, new bases are added following the rules of base pairing

Page 32: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•Elongation of new DNA at the replication fork is catalyzed by enzymes called DNA polymerases (enzymes that catalyzes the elongation of new DNA at a replication fork by the addition of nucleotides to the existing chain)

Page 33: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•The DNA molecule _______, or unzips, into two strands

↓Each strand of the DNA molecule serves as a _______, or model, to produce the new strands

↓Two new ___________ strands are produced, following the rules of _________

separates

template

complimentary

Base pairing

Page 34: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

Page 35: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•The two strands of DNA are anti-parallel (their sugar phosphate backbones run in opposite directions)

•In the double helix, the two sugar-phosphate backbones are upside down relative to each other

Page 36: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•The 5’ to 3’ direction of one strand runs counter to the 5’ to 3’ of the other

Page 37: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•DNA polymerases only add nucleotides to the free 3’ end of a growing DNA strand, never to the 5’ end

•A new DNA strand can only elongate in the 5’ to the 3’ direction

Page 38: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•DNA polymerase adds nucleotides to a complimentary strand as the replication fork progresses

•The DNA strand made by this mechanism is called the leading strand

Page 39: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.

DNA Replication

•To elongate the other new strand of DNA, DNA polymerase works along the other template strand in the direction away from the replication fork

•DNA synthesized in this direction is called the lagging strand

Page 40: DNA Structure. Frederick Griffith In 1928, Frederick Griffith wanted to learn how certain types of bacteria produce pneumonia Griffith injected mice with.