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BIOL332 > Story of DNA > Flashcards

Story of DNA Flashcards

1
Q

What did Hunt know?

A

Knew about genes + Linkage + chromosomes

Knew chromosomes contain genes and they are hereditary material BUT they didn’t know what they were made of

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2
Q

Griffith experiment (overall)

A

Transforming Principal –> Griffith claimed there must be a “transforming principle” that converted Pseudomonas from rough to smooth

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3
Q

Griffith experiment

A

Transforming Principle

Griffth = was a bacteriologist trying to develop a vaccine for Pnuemonia
- Had a strain of Step Pnumoniae (causes Pnumonia)

Strains:
1. Non-viraent R (rough) –> Mouse doesn’t die
2. Virulent (Smooth) –> mouse dies

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4
Q

Griffith Experiment results

A

Heat kills smooth strain – virulent strain but killed first

Rough – can get non-virulent strain from alive mice

Smooth – get strain from dead mouse

Heat killed smooth –> get no virus from mouse

Rough strain and heat killed smooth strain –> Can get virulent smooth strain from mouse

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5
Q
A

If have strep not causing virus and inject self with virulent = will turn non-virulent in body to virulent

Means that this is a bad vaccine strategy

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6
Q

What are possibilities to cause Transforming principle

A

DNA
Proteins
RNA
Lipids (Fats)
Polysaccarides

They knew the transforming principle happened + knew these molecules existed but didn’t know how they work together

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7
Q

Research in great depression

A

Research into DNA was stalled due to the Great Depression – no money to do research

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8
Q

Oswald Avery Colin + Macleod-Maclyn Mccarty (overall)

A

Looking at what causes Transforming Principle

They repeated Griffth’s experiment + they added enzymes (proteases) that could degrade specific substances to mixtures prior to injections
- They took heat killed smooth + rough + dofferent enzymes (one added proteases; one added RNAs etc.)

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9
Q

Results of Oswald Avery Colin + Macleod-Maclyn Mccarty experiment

A

Result: DNA prevents Smooth from converting rough to smooth = DNA is transforming principle

Showed DNA = what the transforming principle is == only one where when we take it away (when degrade it) the mouse lives

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10
Q

Critism in Oswald Avery Colin + Macleod-Maclyn Mccarty experiment

A

Overall – “HOW could 4 nucleotides explain ALL heredity”
- Proteins are more complicated than DNA and proteins do stuff so it was though that special proteins were likely the important hereditary material
- No one believed them because biochemists knew Amino Acids make proteins –> Knew DNA only had 4 nucleotides – thought 4 nucleotides was way to simple to cause the Transforming principle = thought it was protein
- People believed Amino Acids were what was important

Criticism:
1. Your DNA preps are not pure –> 1% of proteins still present even the best of DNA preps

Issue with criticism = bas to make a conclusion then find science that supports it

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11
Q

What did biochemists show (during DNA story)

A

At the time there was a lot of research with radioactive materials

Shows:
1. Proteins have sulfar; DNA does not
2. DNA has phosphate groups; proteins do not

BOTH have Nitrogen

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12
Q

Bacteriophage Cycle

A

Phage sits on E.Coli and injects something in cell and virus does not actually enter cell
- There is something in cell that makes more cirus

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13
Q

Alfred hershey + Martha Chase Experiment (Overall)

A

Hershey + Chase = were viroligists studying bacteriaphage

Knew that phage was simple + comprised only of protein and DNA (no lipids or carbs)
- Knew enough to transform something –> could replicate virus with something

Hypothesis – Either protein or DNA is the heretible material

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14
Q

Use of bacteria Phage

A

Good system to figure out if hereditary material is DNA or protein

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15
Q

Hershey + Chase experiment

A

Used radiolabeled Proteins and DNA

Labeled:
Proetins – 35S –> Only thing that has sulfar
DNA – 32P – only thing with phosphorous
- Virus took radiolabeled DNA

If proteins was the Transforming principle the s35 would be in the cell (radioactive would be in the supernatenet)
- Have rediolabel in celll if proetins ate labeled

If DNA was the Tranforming principle then P32 would be in the infected cell (radioactivity would be in pellet)
- Only radioactive in cell if have radioactive DNA

Results:
When phage has radioactive sulfar –> Radioactivity was in the supernatenet

When DNA was labeled –> radioactivity was in pellet

SHOWS that DNA was injected into E.coli – allows virus to replicate itself

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16
Q

Blender experiment

A

Part of Hershey Chase Experiments

Virus sticks to cell –> could isolate bacteria but radioactive virus will still be on the cell = put in blender
- Blender helps virus detatch from cell

THEN centrifuge –> cells pellet to bottom and the supernatent should have the virus no longer attatched

AFTER blender:
If portein is TP – radioactive in the pellet

If DNA is TP then Radioactive would be in the pellet

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17
Q

What allows Virus to replicate itself

A

Clear DNA injected into the pellet allows Virus to replicate itself

18
Q

What happened after discovered DNA was the hereditary material?

A

The race to solve the structure of DNA began

Before this = started to find the structure of proteins + knew DNA was the hereditary material

19
Q

Chargaff

A

Found:
1. Number of As = Numbers of Ts
2. Number of Gs = Number of Cs

Reason = because of H-bonds holding them together

True in all species BUT different species can have different G-C content

20
Q

How do we find structure of DNA

A

X-ray Diffraction –> get structure of DNA

Steps:
Take structure –> Blast with X-ray –> Anything that hits DNA/protein is refracted light in different directions –> get seperation of light on image film –> can deduce distance away from the mean
- From parameters you can work backwards to find the structure

21
Q

Issue with X-Ray diffraction

A

Get the structure of DNA BUT DNA can take different forms

Issue: DNA is dynamic but X-ray need one static structure
- Initial X-ray pictures were a mess (the result of a mixture of DNA forms in crystals) – couldn’t interpret
- Because DNA can take many forms

22
Q

Forms of DNA

A

DNA can take several forms – A, B, and Z

***Need different forms during different times – DNA can be dynamic

23
Q

A form of DNA

A

More compact

Favored under low water conditions

dsRNA

Some DNA/RNA hybrids

24
Q

Z form of DNA

A

Less compact

Transient structure

No major/minor groove

Favored under high dGC + High salt

Induced by negitive supercoiling

25
Q

Structure of DNA is…

A

DNA structure is Dynamic –> Need to unwind to get to DNA

During unwinding = need to change shape of DNA

26
Q

The race to solve the structure

A

Rosalind Franklin – X-ray Crystolographer
- Did not get along with Wilkins

Maurice Wilkins – X-ray Crytsolographer

James Watson + Crick – Crystologrpher
- Watson/Crick + Pauling –> were talking in Mens club – they all wanted to get the answer before Linnus Pauling

Linnus Pauling – Got nobel prize for covalent theory

27
Q

Linnus Pauling

A

Trying to find structure of DNA – He built a model and then tried to get the data to match the model

Model = Triple elix

28
Q

Rosalin Fraklin

A

It was HER image that helped solve the actual structure of DNA
- She was an X-Ray crystolograoher – meticulous

Approach – she would not build model before data –> She wanted to get the data and then build the model – “Purist”

Contirbutions:
1. Coal and Graphite sturctures – Looking at structure if Carbon
2. DNA structure
3. Virus Structures (Polio)

2 Nobel prizes were awarded to others after her death for DNA and Viral Structures

29
Q

Wilkins model

A

First double helix model BUT the bases point outwards
- Nucleotides face outwards

***Made Rosolin mad because this did not match the data

30
Q

Wilkins + Rosolin Relationship

A

They did not get along

Wilkins thought Rosalion would be a teachnition BUT she thought she would be equal
- She got mad at Wilkins about his model because the data did not match the model he built

31
Q

Photo 51 (Story)

A

Roslin took image – Wilkins saw the image and brought it to the mens club and shared it with Watson + Crick

After seeing the pictire Watson/Crick realized that this meant that DNA has double helic were the nucelotides face inwards – solved the structure once they saw the picture

They solved the structure after they saw the picture – From this image W/C new that DNA was a double helix (not triple) and they knew the distance between the bases and that the bases were pointing inwards

32
Q

W/C model

A

After seeing the picture – built a new model that had the bases pointing inwards stacking together in wats that were consistent with Franklins Photo
- They published the model without Photo 51
- Rosolin saw the paper and asked where the data was –> She left Wilkins lab because she was so fed up

W/C got all of the credit

33
Q

Rosolin after picture

A

Left Wilkins lab + She published work but it was placed at the end of the journal + lacks novelty
- She did publish her work – including the location of water molecules in the same issue but it was put after the W/C paper and lacked notoriety

W/C got all of the credit

THEN Franklin moved to a new instatute where she worked in the structures of RNA viruses and polio virus

She dies of Ovarian Cancer – Hypothesized that it was due to radiation damage + Ashkenazi Jew

34
Q

Sexism in Science

A

W/C + Wilkins did not acknowledge contrubution of Roslin Franklin BUT W/C + Wilkins got nobel prize

35
Q

Watson was…

A

SEXIST – made many sexist + Racist + Abelist commensts and never apologized for his beleifs
- Wouldm’t hire someone that was overweight
- Thought women shouldn’t work in a lab with men
- Promoted genetic screening to increase buety + inteligence + Behaviores (Eugenics)
- Proposed that all traits were entirelly genetiocs and linked to different races

He was forced to retire from Cold Spring Harbour + CSHL tittles revoked

36
Q

What did DNA strcuture provide

A

The Structure of DNA provided a way to understand how DNA can be copied during inheritance

“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for genetic material”

37
Q

Overall Timeline

A
38
Q

DNA Structure

A

Typically found in the B double helix conformation

10 BP/turn

Has major + Minor grooves

39
Q

Use of Major/Minor Grooves

A

Major and Minor grooves provide protein recognition sites

Bind to major – Sequence specific DNA binding proteins typically bind to major groove
- Example = Transcription Factors

Bind to minor – Non-specific DNA Binding proteins typically bind to minor groove
- Example – Histones

40
Q

Where does transcription occur

A

Eurochromatin – regions of transcriptional activity

Shows chromatin can be remodeled

Example – Chromosomal puffs in Drosphilla show states of de-condensing in regions being actively transcribed

BIOL332 (25 decks)

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