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Section 10-1
VOCABULARY REVIEW
1. A virulent strain of a bacterium is one that causes
disease.
2. Transformation is the transfer of genetic material
from one cell to another cell or from one organism
to another organism.
3. A bacteriophage is a virus that infects bacteria.
MULTIPLE CHOICE
1. a 2. c 3. d 4. a 5. b
SHORT ANSWER
1. to show that live R cells are not virulent
2. to show that live S cells are virulent and can kill a
mouse
3. to show that heat-killed S cells do not cause disease
4. to show that something in the heat-killed S culture
was acting on the live R cells to kill the mouse;
experiment 3 showed that it was not the killed S
cells themselves that killed the mouse.
5. The slippery capsule prevents the cells of the
defense system from capturing and destroying
the bacterial cells.
STRUCTURES AND FUNCTIONS
1. Experiment 2
2. Experiment 1
Section 10-2
VOCABULARY REVIEW
1. A purine is a nitrogenous base with two rings of
carbon and nitrogen atoms. Examples may include
adenine or guanine.
2. A pyrimidine is a nitrogenous base with one ring
of carbon and nitrogen atoms. Examples may
include cytosine or thymine.
3. A complementary base-pair is a pair of nitrogenous
bases connected to each other by hydrogen
bonds. Examples may include adenine-thymine
and cytosine-guanine.
4. A nitrogenous base is a base in DNA containing
nitrogen and carbon.
MULTIPLE CHOICE
1. c 2. d 3. a 4. b 5. b
SHORT ANSWER
1. The three parts are a deoxyribose sugar, a phosphate
group, and a nitrogenous base. The phosphate
group and the base are connected to different parts
of the sugar.
2. Since guanine and cytosine are complementary,
another 15% of the nucleotides must contain
cytosine. The remaining 70% of the nucleotides
(100%–30%) must contain adenine and thymine in
equal proportions (35% each), since they are complementary
to each other.
3. Complementary base pairing is important because
the hydrogen bonds between the bases hold the
two strands of DNA together and because it serves
as a way for DNA to replicate.
4. The X-ray diffraction photographs showed that the
shape of the DNA molecule was a double helix.
STRUCTURES AND FUNCTIONS
a, deoxyribose; b, guanine; c, adenine;
d, phosphate group
Section 10-3
VOCABULARY REVIEW
1. A replication fork is a Y-shaped region that results
when the two strands of DNA separate during
replication.
2. A helicase is an enzyme that separates the strands
of DNA during replication.
3. Semi-conservative replication produces a new
DNA molecule with one original strand and one
new strand.
MULTIPLE CHOICE
1. b 2. a 3. b 4. d 5. c
SHORT ANSWER
1. Replication occurs simultaneously at many origins
along the DNA.
2. Producing exact copies ensures that when a cell
divides, the offspring cells will receive the same
genetic information as the parent cell.
3. Cancer can result when errors occur in the replication
of DNA in genes that control how a cell
divides. A mass of cancerous cells called a tumor
can result.
4. The hydrogen bonds break easily, making it easier
for the two strands in the molecule to separate
during replication. The strong covalent bonds
ensure that the sequence of nucleotides remains
fixed in each strand.
STRUCTURES AND FUNCTIONS
Part a: helicase enzymes separate DNA strands;
Part b: DNA polymerase enzymes add complementary
nucleotides to each original strand of DNA and covalent
bonds form between adjacent nucleotides;
Part c: DNA polymerases finish replicating DNA and
fall off, two DNA molecules identical to original DNA
molecule have formed.
Section 10-4
VOCABULARY REVIEW
1. A codon is a sequence of three mRNA nucleotides
that codes for a specific amino acid or a start or
stop signal.
2. Translation is the process of assembling polypeptides
from information encoded in mRNA.
3. An anticodon is a sequence of three tRNA
nucleotides that pairs with a specific codon.
MULTIPLE CHOICE
1. a 2. d 3. b 4. b 5. b
SHORT ANSWER
1. The anticodons are UAC, GUA, CGU, and UCA.
(The last three nucleotides in the mRNA sequence
are a stop codon, which has no anticodon.) The
polypeptide will initially contain four amino acids.
2. The tRNA that pairs with the start codon on
mRNA carries methionine.
3. RNA contains ribose; DNA contains deoxyribose.
RNA usually contains uracil in place of thymine.
RNA is single stranded; DNA is double stranded.
4. All of the codons from the deletion point to the
end of the transcript would be shifted by one
nucleotide, so the sequence of amino acids specified
from that point on would be different.
Translation would terminate prematurely if the
shift resulted in a new stop codon before the end
of the transcript.
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Modern Biology Study Guide Answer Key
STRUCTURES AND FUNCTIONS
a, polypeptide or protein; b, peptide bond;
c, amino acid; d, tRNA; e, anticodon; f, codon; g, mRNA
or transcript; h, ribosome