A1.2 HL Investigating the DNA Molecule
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What type of viruses were used in the Hershey-Chase experiment?
Bacteriophages (viruses that infect bacteria).
What did the Hershey-Chase experiment demonstrate about genetic material?
DNA, not protein, is the hereditary material.
Where was the radioactivity found in each batch after infection?
Sulfur (protein) → liquid; Phosphorus (DNA) → pellet (inside bacteria).
How were proteins and DNA labeled in the Hershey-Chase experiment?
Protein was labeled with radioactive sulfur (³⁵S), DNA with radioactive phosphorus (³²P).
State the two key rules from Chargaff’s work.
1) A=T, 2) G=C.
What assumption did Hershey and Chase make about DNA across organisms?
DNA is the same in viruses, bacteria, and eukaryotes in function.
How would results differ if protein carried genetic information? - hershey and chase
Radioactive protein would enter bacteria instead of DNA.
What did Albrecht Kossel discover in Chargaff’s Rules?
The five nucleotide bases: A, T, C, G, U.
What was the tetranucleotide hypothesis?
DNA made of repeating ATCG units, equal proportions, unable to store info.
How did Chargaff’s data contradict the tetranucleotide hypothesis?
Amounts of A ≠ C ≠ G ≠ T; A=T, G=C; sequences vary → DNA stores information.
How did Chargaff measure base composition?
Acid hydrolysis → chromatography → UV-vis spectroscopy.
How did Chargaff measure base composition?
Acid hydrolysis → chromatography → UV-vis spectroscopy.
How does base variability allow DNA to store genetic information?
Different sequences of bases encode different traits.
Which base pairs with cytosine in DNA?
Guanine.
Which base pairs with thymine in DNA?
Adenine.
What are the three components of a nucleotide? (Refer to diagram for flashcard)
Phosphate group, pentose sugar, nitrogenous base.
Two differences between DNA and RNA?
DNA: Thymine, deoxyribose; RNA: Uracil, ribose.
How many hydrogen bonds hold A-T and C-G together?
A-T = 2; C-G = 3.
Why is water important for life?
Solvent for reactions, medium for metabolism, maintains temperature stability.
Match water properties: cohesion, adhesion, thermal, solvent
Cohesion → insects on water; Adhesion → capillary action; Thermal → water temp stable; Solvent → plasma transport.
keywords for hershey chase expirement
Bacteriophage, E. coli, isotopes (³⁵S, ³²P), centrifugation, pellet, supernatant, hereditary material
keywords for chargaffs rule
Paper chromatography, base composition, complementary, species variation, falsify hypothesis
keywords for DNA structure and function
Hydrogen bonds, complementary base pairing, nucleotide, phosphate, pentose sugar, nitrogenous base