Bio 2100 Latest Exam 4 Assignment
Questions and Verified Answers
(2025).
Why were proteins originally assumed to be the genetic material of the cell? - Answer -
proteins were identified as a class of macromolecules with great heterogeneity and specificity of
function, which are essential requirements for hereditary material
-little was known about nucleic acids, whose physical and chemical properties seemed too
uniform
Griffith - Answer Had two strains of strep bacteria: a pathogenic one and a nonpathogenic
one; found that when he killed the pathogenic bacteria with heat and then mixed the cell
remains with living bacteria of the nonpathogenic strain, some of the living cells became
pathogenic (TRANSFORMATION) --> this newly acquired trait of pathogenicity was inherited by
all of the descendants of transformed bacteria
Transformation - Answer A change in genotype and phenotype due to the assimilation of
external DNA by a cell; transforming substance is DNA
Bacteriophages - Answer viruses that infect bacteria
Hershey and Chase's Experiment With Phages - Answer Experimented with T2, one of many
phages that infect E.coli; used a radioactive isotope of sulfur to tag protein in one batch of T2
and a radioactive isotope of phosphorus to tag DNA in a second batch --> because protein, but
not DNA, contains sulfur, radioactive sulfur atoms were incorporated only into the protein of the
phage; separate samples of nonradioactive E.coli cells were then infected with the protein-
labeled and DNA-labeled batches and observed after onset of infection
RESULTS: radioactive phage DNA entered the bacterial cells, but phage proteins did not; shows
that DNA must be the genetic material
Components of DNA molecules - Answer a nitrogenous base (A, T, G, or C), a pentose sugar
(deoxyribose), and a phosphate group
Chargaff - Answer analyzed the base composition of DNA from a number of different
organisms and found that it varies from one species to another; found that in each species, the
, (2) For each species, the percentages of A and T bases are roughly equal, as are those of G and C
bases
Which bases are purines and which basis are pyrimidines? - Answer Purines (two rings): A and
G
Pyrimidines: C, U, and T
Rosalind's X-ray Diffraction Image of DNA - Answer pattern in this photo implied that the helix
was made up of two strands, forming a double helix; sugar-phosphate bones are located on the
outside of the DNA molecule; her model put negatively charged phosphate groups facing the
aqueous surroundings, while the relatively hydrophobic nitrogenous bases were hidden in the
interior
Watson and Crick's Model of DNA - Answer DNA is a double helix; antiparallel (subunits of the
two sugar-phosphate backbones run in opposite directions)
A must pair with T and G must pair with C in order for a uniform diameter to produced (as seen
in the X-ray image); base pairing is also dictated by the fact that adenine can form two hydrogen
bonds with thymine and only thymine and guanine can form three hydrogen bonds with
cytosine and only cytosine
Given a polynucleotide sequence such as GAATTC, explain what further information you would
need in order to identify which is the 5' end. - Answer You would need to know which end has
a phosphate group on the 5' carbon (5' end) or which end has an -OH group on the 3' carbon (3'
end)
Based on his previous results (living S cells result in dead mouse, living R cells result in healthy
mouse, and heat-killed S cells result in healthy mouse), what result was Griffith expecting when
mixing the heat-killed S cells with the living R cells? - Answer He was expecting the mouse to
remain healthy because neither type of cell alone would kill the mouse
Overview of DNA Replication (Steps) - Answer (1) The parental molecule has two
complementary strands of DNA. Each base is paired by hydrogen bonding with its specific
partner
(2) First, the two DNA strands are separated. Each parental strand can now serve as a template
for a new, complementary strand
(3) Nucleotides complementary to the parental strand are connected to form the sugar-
phosphate backbones of the new "daughter" strands
Questions and Verified Answers
(2025).
Why were proteins originally assumed to be the genetic material of the cell? - Answer -
proteins were identified as a class of macromolecules with great heterogeneity and specificity of
function, which are essential requirements for hereditary material
-little was known about nucleic acids, whose physical and chemical properties seemed too
uniform
Griffith - Answer Had two strains of strep bacteria: a pathogenic one and a nonpathogenic
one; found that when he killed the pathogenic bacteria with heat and then mixed the cell
remains with living bacteria of the nonpathogenic strain, some of the living cells became
pathogenic (TRANSFORMATION) --> this newly acquired trait of pathogenicity was inherited by
all of the descendants of transformed bacteria
Transformation - Answer A change in genotype and phenotype due to the assimilation of
external DNA by a cell; transforming substance is DNA
Bacteriophages - Answer viruses that infect bacteria
Hershey and Chase's Experiment With Phages - Answer Experimented with T2, one of many
phages that infect E.coli; used a radioactive isotope of sulfur to tag protein in one batch of T2
and a radioactive isotope of phosphorus to tag DNA in a second batch --> because protein, but
not DNA, contains sulfur, radioactive sulfur atoms were incorporated only into the protein of the
phage; separate samples of nonradioactive E.coli cells were then infected with the protein-
labeled and DNA-labeled batches and observed after onset of infection
RESULTS: radioactive phage DNA entered the bacterial cells, but phage proteins did not; shows
that DNA must be the genetic material
Components of DNA molecules - Answer a nitrogenous base (A, T, G, or C), a pentose sugar
(deoxyribose), and a phosphate group
Chargaff - Answer analyzed the base composition of DNA from a number of different
organisms and found that it varies from one species to another; found that in each species, the
, (2) For each species, the percentages of A and T bases are roughly equal, as are those of G and C
bases
Which bases are purines and which basis are pyrimidines? - Answer Purines (two rings): A and
G
Pyrimidines: C, U, and T
Rosalind's X-ray Diffraction Image of DNA - Answer pattern in this photo implied that the helix
was made up of two strands, forming a double helix; sugar-phosphate bones are located on the
outside of the DNA molecule; her model put negatively charged phosphate groups facing the
aqueous surroundings, while the relatively hydrophobic nitrogenous bases were hidden in the
interior
Watson and Crick's Model of DNA - Answer DNA is a double helix; antiparallel (subunits of the
two sugar-phosphate backbones run in opposite directions)
A must pair with T and G must pair with C in order for a uniform diameter to produced (as seen
in the X-ray image); base pairing is also dictated by the fact that adenine can form two hydrogen
bonds with thymine and only thymine and guanine can form three hydrogen bonds with
cytosine and only cytosine
Given a polynucleotide sequence such as GAATTC, explain what further information you would
need in order to identify which is the 5' end. - Answer You would need to know which end has
a phosphate group on the 5' carbon (5' end) or which end has an -OH group on the 3' carbon (3'
end)
Based on his previous results (living S cells result in dead mouse, living R cells result in healthy
mouse, and heat-killed S cells result in healthy mouse), what result was Griffith expecting when
mixing the heat-killed S cells with the living R cells? - Answer He was expecting the mouse to
remain healthy because neither type of cell alone would kill the mouse
Overview of DNA Replication (Steps) - Answer (1) The parental molecule has two
complementary strands of DNA. Each base is paired by hydrogen bonding with its specific
partner
(2) First, the two DNA strands are separated. Each parental strand can now serve as a template
for a new, complementary strand
(3) Nucleotides complementary to the parental strand are connected to form the sugar-
phosphate backbones of the new "daughter" strands
