The four important characteristic of genetic material:
- The genetic material must contain complex information
–> store large amounts information - The genetic material must replicate faithfully
–> At each cell division, the genetic material must be correctly and accurately passed down - The genetic material must encode phenotype
–> The genetic material – genotype – must have the capacity to be expressed as a phenotype - The genetic material must have the capacity to vary
–> Genetic material must have the capacity to vary
Johann Friedrich Miescher
- He studied Pus – WBC matter and have large nuclei
- He established that nuclear material contained a novel substance that was slightly acidic and high in phosphorus
- Miescher called its nuclein –> latter called nucleic acid
Albrecht Kossel
Determined that DNA contained four nitrogenous bases: Adenine, Cytosine, Guanine, and Thymine
Phoebus Aaron Levene
- He discovered that DNA consist of a large number of repeating units called nucleotide
- He incorrectly proposed that DNA consists of a series of four-nucleotide units, each containing all four bases – adenine, guanine, cytosine, and thymine – in a fixed sequence
- This concept, known as tertanucelotide hypothesis, implied that the structure of DNA was not variable enough to make it the genetic material
Erwin Chargaff
- He discovered that DNA from different organisms varies greatly in base composition…this finding disapproved tertanucelotide hypothesis
- The amount of adenine is always equal to the amount of thymine A = T
- The amount of guanine is always equal to cytosine G = C
- The amount of purines = pyrimidines
- A+G/T+C = ~1
Mendel
Identified the basic rules of heredity
Explain Fred Griffith Experiment
- Type IIIS virulent bacteria are injected into a mouse –> The mouse dies
- Type IIR noonvirulent bacteria are injected into a mouse –> The mouse lives
- Heat-killed Type IIS bacteria are injected into the mouse –> The mouse lives
- A picture of type IIR bacteria and heat-killed type IIIS bacteria is injected into a mouse –> The mouse dies***Interesting
Conclusion: A substance in the heat-killed virulent bacteria genetically transformed the type IIR bacteria, and now there are live virulent IIS bacteria in the dead mouse in observation #4
Transforming Principle
Substance responsible for transformation
–> DNA
What are something that Griffith considered?
- He considered the possibility that he had not sufficiently sterilized the type IIS bacteria and thus a few live bacteria remained in the culture
–> Not really because Heat-killed bacteria indeed cause NO HARM - IIR bacteria had mutated to the virulent S form
–> Not really because too many mutations
Explain Oswald Avery, Colin MacLeod, and Maclyn McCarty Experiment
Objective: They succeeded in isolating and partially purifying the transforming substance: they showed that it has chemical compositions close to DNA and quiet different from proteins
- Used heat to kill virulent bacteria, homogenize and filter
- Treat samples with enzymes that destroy proteins, RNA, or DNA
- Add the treated samples to cultures of type IIR bacteria
- Cultures treated with protease or RNaases contained transformed type IIS bacteria
- Culture treated with DNases did not
Conclusion: Because only DNase destroyed the transforming substance, the transforming substance is DNA
Phage
Reproduced by attaching to the outer wall of a bacteria cell and injecting its DNA into the cell, where it replicates and directs the cell to synthesize phase protein
T2 Phage
50% protein and 50% DNA
Isotopes
Different forms of an element that have the same number of proteins and electrons but differ in the number of neutrons in the nucleus
–> P32 for bacteria and S35 for protein
Explain Alfred Hershey and Martha Chase Experiment
Experimental Question: Which part of the bacteriophage – its DNA or its protein – serves as the genetic material and is transmitted to phage progeny?
- Infect E.coli grown in medium containing S35 and Infect E.coli grown in medium contain P32 in different container
- S35 is taken up in phage protein, which contain sulphur and not phosphorous, and P32 is taken up in phage DNA, which contains Phosphorous not sulphur
- Phages with S35 infect unlabeled E.coli, and Phages with P32 infect unlabelled E.coli in a different container or vessel
- The protein coats are sheared off, and proteins are separated from bacteria cells by centrifugation –> The bacteria cells contain the progeny phages***
- After centrifugation, S35 is recovered in the virus coats and the infected bacteria pellet contained P32
Since…no radioactivity is detected in phage proteins for S35…the protein was not transformed to progeny
The radioactivity was indicating in phage progeny, DNA had been transmitted to the progeny
Conclusion: DNA — NOT protein – is the genetic material in bacteriophages
X-ray Diffraction
Method for analyzing the three-dimensional shape and structure of a chemical substance in which crystals of the substance are bombarded with X-rays, which hit the crystals, bounce off, and produce a pattern of spots on the detector
The spots provide information about molecular structure
Rosalind Franklin
She discovered the structure of DNA through X-ray diffraction technique
James Watson and Francis Crick
They deduced the structure of DNA based on Rosalind Franklin’s x-ray diffraction image
- Two strands run antiparallel
- Right-handed helix
- sugars and phosphates on the outside…with nitrogenous bases in the inside
Explain Heinz Fränkel-Conrat and Sea Singer – Tobacco Mosaic Virus Experiment
*** The tobacco mosaic virus possesses a single molecule of RNA surrounded by a helically arranged cylinder of protein molecules
Rationale: Fraenkel-Conrat found that after separating the RNA and the protein of TMV, he could remix the RNA and protein of different strains of TMB and obtain, intact, infection viral particles
- They degrade both TMV viruses to yield RNA and protein coat
- They mismatch the RNA and protein coat of Type A and Type B to Create hybrid viruses
- They infect the hybrid viruses on tobacco plants
- The type of RNA in the hybrid parent TMV determined the RNA and protein of the progeny viruses
- They determined that the genetic material of TMV was RNA
Conclusion: Viruses contain Genetic Material
B-DNA
Right-handed helical structure of DNA hat exists when water is abundant; the secondary structure described by Watson and Crick and probably the most common DNA structure in cells
A-DNA
Right-handed helical structure of DNA that exists if less water is present
Hairpin
Secondary structure formed when sequences of nucleotides on the same polynucleotide strand are complementary and pair with each other
