Genes are made of DNA (11.1)
Objectives
1.
Describe Griffith's experiments and conclusion.
2.
Describe Avery's experiments and conclusion.
3.
Explain how experiments with viral DNA further supported Avery's
conclusion.
Key Terms

virus

bacteriophage
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Griffith's "Transforming Factor"
Is the Genetic Material
- Griffith showed that although a deadly strain of bacteria could be made harmless
by heating it, some factor in that strain is still able to change other harmless
bacteria into deadly ones. He called this the "transforming factor."
Avery Shows DNA Is the Transforming Factor
- To test whether protein was the transforming factor, they treated Griffith's
mixture of heat-treated deadly strain and live harmless strain with proteindestroying enzymes, then DNA destroying enzymes.
Virus Experiments Provide More Evidence
-
In 1952, biologists Alfred Hershey and Martha Chase conducted a series of
experiments using viruses.
-
virus: package of nucleic acid wrapped in a protein coat that must use a host
cell's machinery to reproduce itself
-
bacteriophage: virus that infects bacteria; also called a "phage"
Virus Experiments Provide More Evidence
- When only phage protein coats were labeled, most of the radioactivity was
detected outside the cells. But when phage DNA was labeled, most of the
radioactivity was detected inside the cells.
- Hershey and Chase offered further evidence that DNA, not proteins, is the
genetic material. Only the DNA of the old generation of viruses is
incorporated into the new generation.
Concept Check 11.1
1. How did Griffith's experiments indicate the presence of a "transforming factor"
in bacteria?
2. What did Avery's experiments add to the knowledge gained from Griffith's
experiments?
3. Describe the experimental design that allowed Hershey and Chase to
distinguish between the two options for genetic material.
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Nucleic acids store information in their
sequence of chemical units. (11.2)
Objectives


Identify the building blocks of DNA.
Describe DNA's structure and the rules for base pairing in DNA.
Key Terms

deoxyribonucleic acid (DNA)

nucleotide

nitrogenous base

pyrimidine

purine

double helix
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The Building Blocks of DNA
-deoxyribonucleic acid (DNA): molecule responsible for inheritance;
nucleic acid that contains the sugar deoxyribose
-nucleotide: building block (monomer) of nucleic acid polymers.
(Contains 3 parts)
1. A ring-shaped sugar called deoxyribose
2. A phosphate group
3. A nitrogenous base: a single or double ring of carbon and nitrogen
atoms with functional groups.
Nitrogenous Bases
-The bases thymine (T) and cytosine (C) are single-ring structures called
Pyrimidine
-Adenine (A) and guanine (G) are larger, double-ring structures called
Purines
Figure 11-6
DNA contains four different nitrogenous bases. Thymine and cytosine have single-ring structures.
Adenine and guanine have double-ring structures.
DNA Strands
-Nucleotides are joined to one another by covalent bonds that connect the
sugar of one nucleotide to the phosphate group of the next.
-sugar-phosphate "backbone.“
Figure 11-7
Nucleotide monomers join together by covalent bonds between the sugar of one nucleotide
and the phosphate of the next, forming a sugar-phosphate backbone.
DNA's Structure
The Double helix and Complementary Base Pairs
p.231
-double helix: two strands of nucleotides wound
about each other; structure of DNA
Figure 11-8
The bases pair up between the two intertwined sugar-phosphate backbones,
forming the double helix discovered by Watson and Crick. A pairs with T, and G pairs with C.
Concept Check 11.2
1. What are the three parts of a nucleotide? Which parts make up the backbone
of a DNA strand?
2. List the two base pairs found in DNA.
3. If six bases on one strand of a DNA double helix are AGTCGG, what are the
six bases on the complementary section of the other strand of DNA?
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