BIOC 2580 Study Guide - Erwin Chargaff, Photo 51, The Double Helix

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1 Dec 2011

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Bioc 2580 final exam notes: dna double helix. Identified dna as genetic material: dna extracted from virulent strain of bacteria injected into non virulent strain of same bacteria resulted in bacterium being transformed into virulent strain, confirmed that the information for virulence was carried in dna. Found that in all cellular dnas the number of a residues were equal to the number of t residues. Same for c and g: known as chargaff"s rules: Sum of purine residues = sum of pyrimidine residues: % of gc and at varied among different organisms. Applied methods of x ray crystallography to study dna: obtained first useful x ray diffraction images. Contains a lot of information about average structure of components of the dna. Had 2 periodicities along the long axis: primary - 3. 4 a secondary 34 a. First need to isolate dna for x ray crystallography. Difficult dna is very long in chromosomes and easily sheared.

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In the Avery, McCleod, and McCarty experiment, live or heat killed virulent S strain bacterial cells (kill mice) and avirulent R strain bacterial cells (do not kill mice) were mixed with each other and with various enzymes before injecting into mice. Which of the following combinations of treatments would result in a transformation event such that transformed bacteria generated after the mixing of these materials would kill mice when injected into them?

i. heat killed S bacteria + heat killed R bacteria + protease
ii. heat killed S bacteria + heat killed R bacteria + RNAse
iii. heat killed S bacteria + heat killed R bacteria + DNAse
iv. heat killed S bacteria + live R bacteria + protease
v. heat killed S bacteria + live R bacteria + RNAse
vi. heat killed S bacteria + live R bacteria + DNAse
vii. heat killed R bacteria + live S bacteria + protease
viii. heat killed R bacteria + live S bacteria + RNAse
ix. heat killed R bacteria + live S bacteria + DNAse

a.i, ii, iv, v, vii, viii

b.iv, v

c.iii, vi, ix

d.vii, viii

e.iv, v, vii, viii

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What are the differences between virulent and temperate bacteriophages? Select all that apply

Prophages that encode virulence factors are always temperate bacteriophages.

Temperate bacteriophages respond differently to healthy and unhealthy host cells.

Only temperate bacteriophage genomes are inherited by bacterial cell division.

Only temperate bacteriophages are capable of lysogeny.

Virulent bacteriophages infect humans as well as bacteria.

Specialized transduction is only performed by temperate bacteriophages.

Generalized transduction is only performed by virulent bacteriophages.

Prophages that encode virulence factors are always virulent bacteriophages.

Only virulent bacteriophages are capable of the lytic cycle.

A representative virulent bacteriophage is T4; a representative temperate bacteriophage is Î».

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4. The table is from work done by Oswald Averyâs research group regarding transformation. The âtransforming principle preparationâ column on the left refers to the heat-treated smooth (virulent) bacteria. SIII refers to smooth bacteria. R refers to rough (nonvirulent). (this table can be search on google by typing the question. Please search to view it because I can't be able to post it. Thanks)

a. Which of the following best describes transformation?

A. The uptake of foreign material into a cell.

B. The conversion of a non-disease-causing bacteria into a disease causing one.

C. The transfer of novel DNA into a cell.

b. Which of the following best describes how Avery contributed to our understanding that DNA is the genetic material based on his transformation experiments?

A. He showed that non-disease causing bacteria could become disease causing bacteria.

B. He showed that addition of a nuclease to a cell sample could block transformation.

C. He showed that addition of a ribonuclease to a cell sample could block transformation.

D. He showed that addition of a protease to a cell sample could block transformation.

c. Which of the following conclusions would you make based on the table above? Select all that apply. A. DNA, and not RNA or protein, is our genetic information.

B. More âtransforming principle preparationâ results in more transformation.

C. All replicates of the experiment produced identical results.

D. Without âtransforming principle preparationâ added to the reaction, transformation cannot happen.

BIOC 2580 Study Guide - Erwin Chargaff, Photo 51, The Double Helix

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