DNA, The Molecule of Heredity (8/23-8/26)

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Robert Brown (Hint: 2)

English scientist

Discovers the nucleus in plant cells     

Friedrich Miescher (Hint: 3)

German scientist

Isolates nuclei from white blood cells in pus

Found an acidic substance he called nuclein

Nuclein (Hint: 4)

Found by Friedrich Miescher

Later changed to nucleic acid

High in phosphorus

Now know part of phosphates in DNA

Walther Flemming (Hint: 6)

German scientist

Looked at newt lung cells

Discovers chromatin and chromosomes

Stained cells with aniline dyes (take up by thread like structures in nucleus)

Coined the term chromatin to describe the stained nuclear material

Described the events of mitosis

Chromatin (Hint: 3)

Coined by Walther Flemming

Found in the nucleus

Contains DNA and proteins

Chromosome

Colored Body

Nucleus (Hint: 2)

Discovered by Robert Brown

The structure in a cell that contains the chromosomes

Phoebus Aaron Levene (Hint: 3)

American scientist

Determined that DNA was made up of a large number of linked nucleotides consisting of a sugar, a phosphate, and one of the four nitrogenous bases

Proposed the tetranucleotide hypothesis

Tetranucleotide Hypothesis (Hint: 2)

Nucleotides were proposed to be in a fixed four base sequence consisting of all four bases

DNA does not have enough variation to carry information

Frederick Griffith (Hint: 4)

English microbiologist

Discovers the Transforming Principle

Was working with two strains of Streptococcus pneumonia around WWII

Known for the Griffith Experiment

R Strain (Hint: 3)

Rough colonies

Non-virulent

No capsule so they are vulnerable to the immune system

S Strain (Hint: 3)

Smooth colonies

Virulent

Have a capsule that allows them to evade the immune system

What was the question proposed in the Griffith Experiment?

Can an extract of dead bacterial cells genetically transform living cells?

Describe the 4 Steps of the Griffith Experiment

1.)    Control: Living S strain injected into mouse; mouse dies

2.)    Control: Living R strain injected into mouse; mouse lives

3.)    S strain killed by heating and injected into mouse; mouse lives

4.)    Dead S strain cells and Living R strain cells injected into mouse; mouse dies

What was the conclusion of the Griffith Experiment

A non-living chemical substance in the heat killed S-strain can genetically transform the non-virulent R strain into live, virulent S strain bacteria!

Transforming Principle (Hint: 2)

Griffith did not know what the substance that caused the R strain to be transformed into S strain, but called it the transforming principle

Hypothesis: Whatever the transforming principle was it was a good candidate for the long sought genetic material

Avery, MacLeod, and McCarty Experiment (Hint: 2)

Used the process of elimination to identify the transforming principle

Extract of heat killed S strain cells were treated with enzymes that destroy protein (proteases), DNA (DNase), and RNA (RNase)

Describe the 4 steps of the Avery, MacLeod and McCarty Experiment

1. Make an extract of heat killed S strain cells

2. Treat three separate tubes with the following enzymes:

   • Protease

   • RNase

   • DNase

3. Add each treated extract to R strain cells

4. Inject mice

What was the result of the Avery, MacLeod and McCarty Experiment?

Protease and RNase treated extracts transform the cultures to S strain, but DNase does not

Protease

Destroys protein

DNase

Destroys DNA

RNase

Destroys RNA

Hershey-Chase Experiment (Hint: 3)

Performed by Alfred Hershey and Martha Chase

Offered further proof of DNA as the genetic material

Worked with bacteriophages

Describe the 4 steps of the Hershey-Chase Experiment

1.)    Grow phage in either _­­³⁵S or ³²P to radioactively label proteins and DNA

2.)    Let phage infect E. coli cells – inject the genetic material into the cells

3.)    Use a blender to knock off the viral coat (CRUCIAL STEP)

4.)    Centrifuge to spin down the bacterial cells

³⁵S (Hint: 2)

Labels proteins

Stays in supernatant

³²P (Hint: 2)

Labels DNA

In the pellet with bacterial cells

Bacteriophage

Virus that infect bacteria

Erwin Chargaff

Discovered Chargaff’s Parity Rule

Chargaff’s Parity Rule (Hint: 2)

In DNA, the composition of bases (ATCG) differed between organisms BUT the amount of A=T and C=G

At the time, the reasons for this was unknown, but was one of the fundamental observations that nucleotides form base pairs

Rosalind Franklin and Maurice Wilkins (Hint: 6)

Pioneer in structural biology

Studied X-ray diffraction pattern of DNA

Conclusion: DNA is a double helical structure with distinctive regularities

0.34 nm between bases

3.4 nm per turn

10 bases per turn of DNA

X-Ray Diffraction (Hint: 4)

X-ray crystallography

Crystals of a substance are bombarded with X-rays, which are diffracted (bounce off)

The Spacing of the atoms within the crystal determines the diffraction pattern, which appears as spots on a photographic film

The diffraction pattern provides information about the structure of the molecule

James Watson and Francis Crick (Hint: 3)

Solved the structure of DNA by using the available evidence from biochemistry and the X-ray diffraction images of Franklin

Built models until they got one that matched the available evidence

No experiments, just theory

What are the 3 incorrect theories of inheritance?

Theory of Pangenesis

Theory of Preformation

Blending Theory of Inheritance

Theory of Pangenesis (Hint: 3)

Proposed by the Greek physician Hippocrates

“Seeds” produced by all parts of the body are collected in the reproductive organs then passed to the offspring at the moment of conception

Probably the most ancient theory of inheritance

Theory of Preformation (Hint: 2)

Homunculus simply develops in the womb

Thought women’s role was to “incubate” the men (shows bias of the time)

Homunculus

“little man” that early microscopists thought they saw in the sperm

Blending Theory of Inheritance

Factors that control heredity traits are malleable and can blend together from generation to generation

List the 4 characteristics of the genetic material?

Contains complex information: Must contain the information necessary to construct a complete organism

Replication: Must be copied faithfully so the information can be passed on to subsequent generations

Transmission of a trait: Must transmit specific traits to subsequent generations

Variation: Must vary in such a way that accounts for known differences in the appearance of organisms

In humans, 20% of bases in DNA are C. What percentage of the bases are expected to be T?

30%