Chapter Two Flashcards
Explain part one of the Griffith Experiment.
In the first part of Griffith Experiment, two strains of Bacteria were chosen.
The first strain was called the rough strain because it had a mutation in one of its genes that did not allow the glycocalyx to form (slimy layer). The second strain had no mutation
The rough strain was not virulent because it had no protection. And the smooth strain was.
Subsequent injection into rat populations showed this.
Explain the second part of the Griffith Experiment and its significance.
In the second part, the smooth strain, which previously had been virulent, was put in a tube and boiled. When injected, the now dead strain had no effect on the mice.
The notable part of this experiment was when the alive rough strain was mixed with the dead smooth strain.
When injected, this killed mice.
The significance of this experiment was that something had been passed by the dead strain to the living strain to overcome the mutation in the R strain, making the glycocalyx - allowing the strain to kill mice.
List the following for the Griffith Experiment:
- Dependent Variable
- Independent Variable
Dependent Variable is whether or not the mice died.
Independent variable is whether the strain was rough, smooth, or a combination of dead and alive.
Explain how Avery expanded upon the work of the Griffith Experiment.
The mix of dead smooth strain bacteria and alive rough strain contained all the macromolecules, and the DNA of the s-strain was somehow mixed with the alive r-strain. They wanted to see what macromolecule was passed (at the time scientists thought it must be protein that is passed on)
They then took the extract and treated it with various enzymes including proteases, DNAases and RNAases.
Each time they mixed the two strains they added a different enzyme.
They saw that, only when the DNAase was added, did the mixture lack a glycocalyx.
Explain the work of the Hershey-Chase Experiment.
In this experiment, bacterial viruses (phages) were used to infect an ecoli host.
Phages simply contain DNA to give instructions to their host, and a structure that is built of protein.
One group used radioactive phosphates (p32) to “mark” the DNA of the progeny in the ecoli.
In the second group, radioactive sulfur was used to mark that of the phages bodies.
The idea of the experiment was to determine if phages passed proteins or DNA to their progeny.
These marked phages were then put in a medium of ecoli that did not contain any isotopes. They wanted to see if the marked phages would produce progeny that contained isotopes. To ensure no compounding variables, the ecoli was scraped to ensure all they saw was the progeny.
They saw that only radioactive phosphates were passed into progeny. Meaning that DNA was only passed and that proteins were not.
What are the purines?
They are the nitrogenous bases of nucleotides and they include Adenine and Guanine.
What are the pyrimidines.
C’s and T’s are pyrimidines.
Cytosine and Thymine and Uracil.
What is a nucleoside?
A nucleoside is the unit for nucleic acids minus the phosphate.
Why is Ribose a tad bit bigger than Deoxyribose?
Because it has an extra Oxygen on the second carbon.
How are chromosomes ordered (for the most part)?
They are ordered by size, except chromosome 21 is actually the smallest.
ex. trisomy 21
errors in the number of chromosomes (say three) is actually impossible to have offspring if the chromosome pair is larger.
You will never see a trisomy of chromosome 1.
In complementary base pairs, which is the strongest and why?
Cytosine to Guanine is the strongest because it contains three hydrogen bonds instead of two seen in Adenine and Thymine.
How did Rosalind Franklin contribute to determining the structure of DNA?
She was an expert in X-ray diffraction, and was recruited to work on the structure of DNA.
She shot X-rays through a pure extract of DNA and the particles show where the structure lies.
She discovered that it was symmetric and that it had major and minor grooves.
Because she was smart, she knew this meant that it must be a helical shape.
How did Francis/Crick expand on the Franklins work?
They were chemists who knew, because it was symmetric, that they only way it could be structured was for one of the strands to be upside-down.
How many base pairs are there in one human cell?
3.5 billion.
How long would it take you to read a book of all the base pairs in a human cell if you treated it like your full time job?
It would take you 30 years.
