8.1 Study Guide Flashcards
Who was the first person to demonstrate and document the Process of Bacterial Transformation and in what year?
Frederick Griffith in 1928
What disease was Griffith researching?
Pneumonia
Why was Griffith’s experiment important?
His “Transforming Principle” experiment was the first experiment which suggested that bacteria can transfer genetic information through a process called transformation.
Describe Griffith’s experiment.
Injected several variations of Streptococcus Pneumoniae bacteria into mice then looked for infection and death.
Experiment:
Group 1- Live R-STRAIN (Mouse lived),
Group 2- Live S-STRAIN (mouse died),
Group 3- Heat-Killed S-STRAIN (Mouse lived),
Group 4- Heat-Killed S-STRAIN and Live R-STRAIN (mouse died), Group 5- Live S-STRAIN from Group 4 (Mouse Died).
Conclusions: R-STRAIN was transformed by S-STRAIN inheriting some “transforming principle” that made it deadly.
Griffith called the process of one strain of bacteria acquiring a “factor” from another bacteria ______?
Transformation
Both the Rough Strain of bacteria and the Heat Killed Smooth Strain did not kill the infected mouse alone. Why did they become deadly once combined?
The Rough Strain of bacteria picked up the genetic material/ traits of the dead smooth strain making it deadly.
What did Griffith think could have been passed from one bacteria type to another?
Proteins, DNA, carbohydrates and lipids
What was the most significant conclusion of Griffith’s experiments with pneumonia in mice?
Bacteria are capable of transferring genetic information through transformation.
What was the Avery-McCloud McCarty Experiment Purpose?
Building off the Griffith Experiment to identify the “Transforming Factor” aka the “Molecule of Inheritance” aka “Genetic Material”. Proving it was either Protein or DNA.
Describe the Avery-McCloud McCarty Experiment.
- Isolated the transforming principle
- Ran many tests (Solubility, Temperature, pH Change, UV, Nitrogen:Phosphorus Ratio, Precipitation
- Compared the results of the tests to known Biological Molecules and determined Proteins, RNA or DNA most likely and Carbohydrates and Lipids were eliminated
- Heat Killed S-STRAIN with Carbohydrates and Lipids removed was added variations of the R-STRAIN described in step 5.
- R-STRAIN was injected into mice looking for infection and death. If the mouse dies then transformation occurred-
Group 1 - Live R-STRAIN (Control) -Mice Died
Group 2- Live R-Strain - No Protein - Mice Died - Proteins not transformation material
Group 3- Live R-STRAIN-No RNA- Mice Died - RNA not transformation material
Group 4 - Live R-STRAIN -No DNA - Mouse lived - DNA is the transformation material
In the Avery-McCloud-McCarty Experiments did transformation still occur without the Proteins?
Yes
In the Avery-McCloud-McCarty Experiments did transformation still occur without the RNA?
Yes
In the Avery-McCloud-McCarty Experiments did transformation still occur without the DNA?
No
Why did the Avery-McCloud-McCarty Experiments conclude that DNA was most likely responsible for transformation?
Transformation only stopped with DNA wasn’t present (it was able to occur without proteins and RNA)
After Avery and team discovered the transforming factor was it immediately accepted by scientist?
No, scientists were skeptical that DNA was the transforming material/ genetic material because they thought the structure of DNA was too simple to be responsible for genetic traits.
What did the Henry-Chase experiments study?
Bacteriophages (viruses that attack bacteria)
What do bacteriophages do to bacteria?
Attached to the bacteria and inject DNA giving the bacteria instructions to make lots of copies of the Bacteriophage
Describe the Hershey-Chase experiment.
- Radiolabeled Bacteriophage with Sulfur 35S (found in Protein) or Phosphorous 32P (found in DNA)
- Each batch of bacteriophage was used to infect a different culture of bacteria.
- After infection, the cultures were centrifuged removing the bacteriophage as the supernatant and isolating the bacteria as a pellet.
- Radioactivity was measured in the pellet and supernatant.
- Large amount of 32P (DNA) were found in the pellet (bacteria) and 35S (Protein) in the Supernatant.
- Conclusion that DNA, not protein, was injected into the bacteria and made up the genetic material of the bacteriophage.
Why does a virus infect a host cell with genetic material?
This is how the virus reproduces
In the Henry-Chase experiment what is the Independent Variable?
Which molecule is radioactively tagged
In the Henry-Chase experiment what is the Dependent Variable?
Whether or not radioactivity is found in the bacteria
In the Henry-Chase experiment, what claim can you make about the virus’s genetic material? What evidence from the experiment supports this?
Viruses use DNA as their genetic material - only radioactive phosphorous (tagged DNA) was found inside of bacterial host cells, no radioactive sulfur (tagged protein) got inside
What are Chargaff’s two Rules?
Rule 1: In any double stranded DNA, the # of guanine units ~ # of cytosine units and the # of adenine ~ # of thymine.
Rule 2: The relative amounts of A, C, G and T varies from one species to the next and accounts for genetic diversity between species
If the DNA has 36% cytosine (C) what percentage of guanine (G), adenine (A) and thymine does the DNA have?
then guanine (G) = 36%. This leaves 100% - (36% + 36%) = 28% for the combination of adenine (A) and thymine (T) or 14% each.
Who discovered that certain bases always pair up in the middle of a DNA strand?
Watson and Crick
What does “A” (Adenosine) pair with?
“T” (Thymine)
What does “G” (Guanine) pair with?
“C” (Cytosine)
What did Watson and Crick learn from Rosalind Franklin’s x-ray crystallography photo of DNA?
- DNA strands were helical
- The distance between nucleotides
- Ten nucleotides between each turn of the DNA molecule
- DNA bases face the inside of the helix
- Phosphate groups face the outside of the helix
- DNA contained two strands
What are the three parts of a nucleotide?
- Sugar
- Phosphate Group
- Nitrogenous Base
What parts of the nucleotides make up the backbone of the DNA strands?
sugar-phosphate backbone
Purines are made up of how many rings?
One
What two nucleotides are purines?
Thymine (T) and Cytosine (C)
Pyrimidines are made up of how many rings?
Two
What two nucleotides are pyrimindines?
Adenosine (A) and Guanine (G)
Purines always pair with pyrimidines to form the _______?
Double Helix structure of DNA
What bonds hold the strands of DNA together?
Weak Hydrogen Bonds between Nitrogenous Bases
What bonds hold the sugar, phosphate and nitrogenous base together?
Strong Covalent Bonds
How do the bonds fit the mechanism for copying DNA?
Weak Hydrogen Bonds facilitate strand separation and base pairing allowing the double helix to easily unwind and separate during replication.
Directionality of DNA is important. The Carbons in the Sugar (Deoxyribose) are numbered with C1’ connected to _____ then C2’-C4’ _________ ending with C5’ bonded to _________.
The Nitrogenous base
Clockwise around Ribose
The Phosphate Group
Nucleotides are bonded from phosphate to sugar between which two Carbons in the sugar (Deoxyribose)?
C3’ and C5’
“Antiparallel” in reference to DNA means that
the two strands of a DNA double helix run in opposite directions to each other
one strand is oriented 5’ to 3’ and the other strand oriented 3’ to 5’,
allows for complementary base pairing between the two strands
What are the two main differences between DNA Nucleotides and RNA Nucleotides?
- DNA contains the sugar deoxyribose while RNA contains ribose
- DNA has the base thymine (T) while RNA has uracil (U) in place of thymine
