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  • 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of
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Page 1: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

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Page 2: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

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Page 3: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

History of DNAEarly scientists thought protein was the

cell’s hereditary material because it was more complex than DNA

Proteins were composed of 20 different amino acids in long polypeptide chains

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Page 4: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

TransformationTransformationFred Griffith worked with virulent S

and nonvirulent R strain Pneumoccocus bacteria

He found that R strain could become virulent when it took in DNA from heat-killed S strain

Study suggested that DNA was probably the genetic material

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Page 5: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Griffith Experiment

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Page 6: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

History of DNAChromosomes are made

of both DNA and proteinExperiments on

bacteriophage viruses by Hershey & Chase proved that DNA was the cell’s genetic material

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Radioactive 32P was injected into bacteria!

Page 7: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Discovery of DNA Discovery of DNA StructureStructure

Erwin Chargaff showed the amounts of the four bases on DNA ( A,T,C,G)

In a body or somatic cell: A = 30.3% T = 30.3% G = 19.5% C = 19.9%

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Page 8: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Chargaff’s RuleChargaff’s RuleAdenineAdenine must pair with

ThymineThymineGuanineGuanine must pair with

CytosineCytosineThe bases form weak hydrogen

bonds

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G CT A

Page 9: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

DNA StructureDNA StructureRosalind Franklin took diffraction x-ray photographs of DNA crystals

In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays

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Page 10: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

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Page 11: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

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Page 12: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Replication FactsReplication FactsDNA has to be copied DNA has to be copied before a cell dividesbefore a cell divides

DNA is copied during DNA is copied during the the SS or synthesis phase or synthesis phase of of interphaseinterphase

New cells will need New cells will need identical identical DNA strandsDNA strands

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Page 13: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Synthesis Phase (S Synthesis Phase (S phase)phase)

S phase during interphase of the cell cycle

Nucleus of eukaryotes

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Mitosis-prophase-metaphase-anaphase-telophase

G1 G2

Sphase

interphase

DNA replication takesDNA replication takesplace in the S phase.place in the S phase.

Page 14: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

DNA ReplicationDNA ReplicationBegins atBegins at Origins of ReplicationOrigins of ReplicationTwo strands open forming Two strands open forming

Replication Forks (Y-shaped Replication Forks (Y-shaped region)region)

New strands grow at the forksNew strands grow at the forks

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ReplicationReplicationForkFork

Parental DNA MoleculeParental DNA Molecule

3’

5’

3’

5’

Page 15: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

DNA ReplicationDNA ReplicationAs the 2 DNA strands open at As the 2 DNA strands open at

the origin, the origin, Replication Replication BubblesBubbles form form

Prokaryotes (bacteria) have a single bubble

Eukaryotic chromosomes have MANY bubbles

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Bubbles Bubbles

Page 16: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

DNA ReplicationDNA ReplicationEnzyme Enzyme HelicaseHelicase unwinds and separates unwinds and separates the 2 DNA strands by the 2 DNA strands by breaking the breaking the weak weak hydrogen bondshydrogen bonds

Single-Strand Binding Single-Strand Binding ProteinsProteins attach and keep the 2 DNA strands separated and untwisted

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Page 17: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

DNA ReplicationDNA Replication BeforeBefore new DNA strands can

form, there must be RNA primersRNA primers present to start the addition of new nucleotides

PrimasePrimase is the enzyme that synthesizes the RNA Primer

DNA polymerase can then add the new nucleotides

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Page 18: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

DNA ReplicationDNA ReplicationDNA polymeraseDNA polymerase can only add can only add

nucleotides to the nucleotides to the 3’ end3’ end of the DNA of the DNA This causes the This causes the NEWNEW strand to be strand to be

built in a built in a 5’ to 3’ direction5’ to 3’ direction

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RNARNAPrimerPrimerDNA PolymeraseDNA Polymerase

NucleotideNucleotide

5’

5’ 3’

Direction of ReplicationDirection of Replication

Page 19: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Remember HOW the Carbons Remember HOW the Carbons Are Numbered!Are Numbered!

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OO=P-O O

PhosphatePhosphate GroupGroup

NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)

CH2

O

C1C4

C3 C2

5

SugarSugar(deoxyribose)(deoxyribose)

Page 20: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Remember the Strands are Remember the Strands are AntiparallelAntiparallel

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P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Page 21: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Synthesis of the New DNA Synthesis of the New DNA StrandsStrands

The The Leading StrandLeading Strand is synthesized as a single strand single strand from the point of origin toward the opening replication fork

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RNARNAPrimerPrimerDNA PolymeraseDNA PolymeraseNucleotidesNucleotides

3’5’

5’

Page 22: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Synthesis of the New DNA Synthesis of the New DNA StrandsStrands

The The Lagging StrandLagging Strand is is synthesized discontinuouslydiscontinuously against overall direction of replication

This strand is made in MANY short segments It is replicated from the replication fork toward the origin

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RNA PrimerRNA Primer

Leading StrandLeading Strand

DNA PolymeraseDNA Polymerase

5’

5’

3’

3’

Lagging StrandLagging Strand

5’

5’

3’

3’

Page 23: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Replication of StrandsReplication of Strands

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Replication Fork

Point of Origin

Page 24: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Proofreading New Proofreading New DNADNA

DNA polymerase initially makes about DNA polymerase initially makes about 1 in 10,0001 in 10,000 base pairing errors base pairing errors

EnzymesEnzymes proofread and correct these proofread and correct these mistakesmistakes

The new error rate for DNA that has The new error rate for DNA that has been proofread is been proofread is 1 in 1 billion1 in 1 billion base base pairing errorspairing errors

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Page 25: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Semiconservative Model of Semiconservative Model of ReplicationReplication

Idea presented by Idea presented by Watson & CrickWatson & CrickTheThe two strands of the parental

molecule separate, and each acts as a template for a new complementary strand

New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA

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Parental DNA

DNA Template

New DNA

Page 26: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

DNA Damage & DNA Damage & RepairRepair

Chemicals & ultraviolet radiation damage the DNA in our body cells

Cells must continuously repair DAMAGED DNA

Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA

DNA polymerase and DNA ligase replace and bond the new nucleotides together

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Page 27: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Question:Question:

What would be the complementary DNA strand for the following DNA sequence?

DNA 5’-CGTATG-3’DNA 5’-CGTATG-3’

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Page 28: 1. 2 History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of

Answer:Answer:

DNA 5’-CGTATG-3’DNA 5’-CGTATG-3’

DNA 3’-GCATAC-5’DNA 3’-GCATAC-5’

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