Chapter 12Chapter 12DNA and GenesDNA and Genes

• Vocabulary:• Transformation

• Bacteriophage

• Nucleotide

• Base pairing

• Double helix

Key Concepts:

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

•What is the overall structure of the DNA molecule?

DNA: The Molecule of Heredity

What we’ve learned so far…

•Cells make proteins

•Genetic information is passed on through chromosomes

•Compacted DNA and proteins= chromosomes•Genetic information is stored in the nucleus

•Genetic information is essential so that each cell is identical (mitosis)

To truly understand genetics, To truly understand genetics, biologists first had to discover the biologists first had to discover the chemical nature of the gene.chemical nature of the gene.How do genes control what you How do genes control what you

look like? look like?

Animal HusbandryGoat herders 5000 years ago knew …

Offspring tend to look like their parents.

DNA’s “Experiment” HistoryDNA’s “Experiment” History

Fredrich Miescher (1869)Fredrich Miescher (1869)

Studied pus cells he collected Studied pus cells he collected from bandages in hospitalsfrom bandages in hospitals

White blood cells are White blood cells are hugehuge..

Used an enzyme to digest Used an enzyme to digest away the proteins in nucleusaway the proteins in nucleus

A strange A strange phosphorousphosphorous molecule remainedmolecule remained

Molecule of heredity?Molecule of heredity?

Griffith: How do certain types of Griffith: How do certain types of bacteria cause pneumonia? bacteria cause pneumonia? The experiment that tested this The experiment that tested this

question led to new knowledge.question led to new knowledge. Genetic information could be Genetic information could be

transformed from one bacterium transformed from one bacterium to another.to another.

Fredrick Griffith (1928)Fredrick Griffith (1928)

Fredrick Griffith (1928)Fredrick Griffith (1928)

He injected mice with the one strain of bacteria He injected mice with the one strain of bacteria and they died.and they died.

When he did the same with another strain of When he did the same with another strain of bacteria they didn’t die.bacteria they didn’t die.

He could use heat to kill the deadly bacteria so it He could use heat to kill the deadly bacteria so it wouldn’t kill mice. wouldn’t kill mice.

Injected mice with a mixture of harmless bacteria Injected mice with a mixture of harmless bacteria and the heat killed bacteria…and the heat killed bacteria…

Genetic Info. Transferred

The mice died!!The mice died!! Something had passed from the heat killed Something had passed from the heat killed

deadly bacteria to the living harmless deadly bacteria to the living harmless bacteria.bacteria.

He called this process He called this process TRANSFORMATION.TRANSFORMATION.

Avery & DNAAvery & DNA Avery and a group of scientists decided to repeat Avery and a group of scientists decided to repeat

Griffith’s experimentGriffith’s experiment determine which molecule in the heat killed bacteria was determine which molecule in the heat killed bacteria was

needed for transformationneeded for transformation Made an extract (juice) from heat killed bacteria and added Made an extract (juice) from heat killed bacteria and added

enzymes that destroy enzymes that destroy proteins, carbohydrates, & lipids Transformation still occurred!Transformation still occurred!

Repeated the experiment but added Repeated the experiment but added enzymes that destroy enzymes that destroy DNA DNA Transformation DID NOT occur!!Transformation DID NOT occur!!

Avery’s ConclusionAvery’s Conclusion

What was the “transforming factor”? What was the “transforming factor”?

DNADNA

Conclusion: Conclusion: DNA is the nucleic acid DNA is the nucleic acid that stores and transmits that stores and transmits genetic info from generation to genetic info from generation to generationgeneration

Hershey-Chase Experiment Hershey-Chase Experiment (1952)(1952)

Studied viruses; specifically bacteriophagesStudied viruses; specifically bacteriophages Bacterio = bacteria Bacterio = bacteria Phage = eaterPhage = eater Bacteria eaterBacteria eater

Viruses—made up of: Viruses—made up of: DNA + protein coatDNA + protein coat

Research Question: Which Research Question: Which part of the viruspart of the virus enters the infected bacteria cell?enters the infected bacteria cell?

Hershey & ChaseHershey & Chase Wanted to REALLY make Wanted to REALLY make

sure it was DNAsure it was DNA Viruses are made of only Viruses are made of only

protein and DNAprotein and DNA Proteins have sulfur but Proteins have sulfur but

no phosphorousno phosphorous.. DNA has phosphorous DNA has phosphorous

but but no sulfurno sulfur

Bacteriophage

Grew viruses in the presence Grew viruses in the presence of radioactive markers Pof radioactive markers P32 and and

SS35. . Sulfur is found in protein coatSulfur is found in protein coat Phosphorus is found in DNAPhosphorus is found in DNA

Hershey-Chase ConclusionHershey-Chase Conclusion

Genetic information of the bacteriophage Genetic information of the bacteriophage

that they infected with bacteria was that they infected with bacteria was DNADNA NOT proteinNOT protein

What DNA does…What DNA does…

Deoxyribonucleic Acid = DNADeoxyribonucleic Acid = DNA Carries information from one generation to Carries information from one generation to

the nextthe next Put that information to work by determining Put that information to work by determining

heritable characteristicsheritable characteristics Must be easily copied since almost every Must be easily copied since almost every

new cell gets a copynew cell gets a copy

DNA StructureDNA Structure

Made up of nucleotides (monomer)Made up of nucleotides (monomer) Each composed of 3 parts:Each composed of 3 parts:

Deoxyribose: sugarDeoxyribose: sugar Phosphate groupPhosphate group Nitrogenous (nitrogen containing) Nitrogenous (nitrogen containing)

basebase• Adenine (A)Adenine (A)• Thymine (T)Thymine (T)• Guanine (G)Guanine (G)• Cytosine (C) Cytosine (C)

BackboneBackbone Deoxyribose & Phosphate Deoxyribose & Phosphate

Group of each nucleotideGroup of each nucleotide

““Steps of Ladder”Steps of Ladder” basesbases

Any base sequence is possible

DNA Structure = Double Helix

Chargaff’s RulesChargaff’s Rules

What does this data suggest to you?What does this data suggest to you?

Percentage of Bases in Four Percentage of Bases in Four OrganismsOrganisms

Source of DNASource of DNA AA TT GG CC

StreptococcusStreptococcus 29.829.8 31.631.6 20.520.5 18.018.0

YeastYeast 31.331.3 32.932.9 18.718.7 17.117.1

HerringHerring 27.827.8 27.527.5 22.222.2 22.622.6

HumanHuman 30.930.9 29.429.4 19.919.9 19.819.8

Oooooohhhh!! Oooooohhhh!! Aaaaaahhhhh!!!!Aaaaaahhhhh!!!!

A = T A = T (A pairs with T)(A pairs with T)C = G C = G (C pairs with G)(C pairs with G)

What DNA Looks LikeWhat DNA Looks Like Rosalind FranklinRosalind Franklin: used X-Ray : used X-Ray

diffraction patterns to discover that DNA diffraction patterns to discover that DNA twisted around each other like a helixtwisted around each other like a helix

Watson & Crick: while Watson & Crick: while trying to build a 3-D trying to build a 3-D model of DNA, Watson model of DNA, Watson was shown Franklin’s was shown Franklin’s photograph and within photograph and within weeks, figured out the weeks, figured out the structure of DNAstructure of DNA

What’s holding the strands What’s holding the strands together?together?

HYDROGEN HYDROGEN BONDS!!!BONDS!!!

Hydrogen Bonds form Hydrogen Bonds form between A and T between A and T base base pairs as well as pairs as well as between C and Gbetween C and G base base pairspairs