Exam 1: Lecture 4 Flashcards Preview

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-single celled prokaryotic organisms
-no nucleus
-transcription and translation not spatially separated as they are in eukaryotic cells



-ancestors of viruses that only infect bacterial cells
-particles contain DNA genome that is packaged into the head of the phage
-upon attachment to a bacterial cell wall by the legs of the phage the baseplate comes in contact with the cell wall and a hole is burrowed into the membrane
-genome passes through the neck and body of the phage and is then injected into the bacterial through the baseplate
-bacterial replication machinery will duplicate the phage genome while the transcription and translation machinery will generate viral mRNAs and proteins


Fredrick Griffith (Transforming Principle)

-published the results of an experiment that demonstrated that a substance within one strain of bacterial cells could alter the character of a second bacterial strain
-used a pathogenic strain of bacteria (S) and a non-pathogenic strain (R). Mice injected with a living S strain would die of a respiratory infection while mice injected with the R strain were unaffected
-heat killed and fragmented the S bacteria and performed two key experiments. Injection of the heat killed/fragmented S strain, on its own, had no effect. However, mice would contract and die of a respiratory infection if they were injected with a mixture of heat killed/fragmented S strain and living population of the R strain
-concluded that the R strain was transformed by a substance from the heat killed/fragmented S strain-->"The Transforming Principle"
-results confirmed Mendel’s theories on inheritance and were the foundation for later experiments the proved that the transforming substance was DNA.
-demonstrated for transformation of bacteria for the first time


X-ray Crystallography

-the structure of complex molecules can be determined by bombarding a crystal (of the subject of interest) with a beam of x-rays.
-when the beam hits the crystal, it is diffracted towards a piece of film.
-resulting image corresponds to atomic structure of substance in question.
-used to determine atomic structure of DNA, proteins, and viruses, and molecular nature of protein-nucleic interactions
-information derrived from structure is used to make drugs/antibodies/vaccines/theraputic anti-cancer drugs.


Rosalind Franklin

-used x-ray crystallography to generate diffraction pattern for crystal of DNA
-in process of solving the structure when Watson and Crick stole her research and solved it themselves.


Watson and Crick

-their structure of DNA was based on Franklin's diffraction pattern and gave her no credit when the won the nobel prize
-at the time of solving, they knew DNA contained nucleotide bases, sugar molecules, and phosphate groups
-they determined that it is composed of two polynucleotide chains that are wound into a double helix.


DNA Double Helix Properties

-comprised of 2 polynucleotide chains
-within in single strand individual nucelotides are joined together through phosphodiester bonds
-the two strands that comprise the double helix are joined together by hydrogen bonding between purine and pyrimidine bases.
-major groove: where DNA binding proteins interact with DNA here
-minor groove: histone proteins interact here


Major Groove

-place where many DNA binding proteins and transcription factors sit down


Minor Groove

-not much chemical information so non-sequence specific proteins sit here


DNA Nucleotide Sturcture

-DNA comprised of 4 building blocks called nucleotides. each consists of purine or pyrimidine base, a sugar moiety and phosphate group.
-purine bases are A and G
-pyrimidine bases are T and C
-based on x-ray diffraction it was determined that the purine bases form hydrogen bonds with pyrimidines.


Erwin Chargaff (Base Pairing and Phosphodiester Bonds)

-isolated nucleic acids from variety of tissues and organisms and determined the percentage of each nucleotide.
-amount of adenine equaled amount of thymine and amount of cytosine was equal to amount of guanine.
-Watson and Crick ripped him off to to postulate that adenine bases formed hydrogen bonds with thymine and cytosine formed hydrogen bonds with guanine.
-amount of each nucleotide differs amongst tissues and organisms but A:T and C:G ratios is always 1:1
-polynucleotide chain is held together by phosphodiester bonds


Double Helix Dynamics: Antiparallel

-poly nucleotide strands oriented anti-parallel to each other
-3' means that #3 carbon will be bound to phosphate group of the next nucleotide
-5' means the #5 carbon will be bound to the deoxyribose sugar in the adjacent nucleotide


Interaction of Bases in Double Helix

-A:T bases interact through 2 hydrogen bonds
-C:G bases interact through 3 hydrogen bases
-amount of energy it takes to separate nucleotides is directly proportional to the number of hydrogen bonds with G:C pairs taking more energy/heat to separate than A:T pairs


Oswald Avery

-repeated Griffity's experiments but conducted set of controls that proved nucleic acid is the hereditary material
-heat killed and fragmented pathogenic S bacterial strain
-employed biochemical methods to separate nucleic acid, protein and lipid fractions
-mixed each fraction with non pathogenic R strain and injected each mixture into mice
-mixtures containing R bacterial strain and either the protein or lipid had no effect
-mice died with mixtures of living R bacteria and nucleic acid from heat killed/fragmented pothegenic S strain were injecte
-transforming agent=DNA


Hershey and Chase

-proved nucleic acid was transforming agent and hereditary material with differen approach
-parasiic interaction between bacteriophage and bacteria.
-phage coat proteins labeled with radioactive sulfur and genome labled with radioactive phosphorus.
-bacteriophage allowed to attach to bacterial cell wall and inject genome into cytoplasm
-empty phage particles removed
-new phage particles later isolated from bacterial cells
-some contained radioactively labeled genomes derived from original phage particles
-others contained non-radioactive genomes-generated by bacterial replication machinery.
-both types of tenomes packaged within non-radioactive phage particles-generated by host transcription translation machinery (not radioactive so not original particles)
-show phage genome was transforming agent and hereditary material