SU 5
DNA and its role in
heredity
Hillis et al., Chapter 13
Sections 13.1-13.4
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Chapter 13 DNA and Its Role in Heredity
Key Concepts
13.1 Experiments Revealed the Function of DNA as Genetic Material
13.2 DNA Has a Structure That Fits Its Function
13.3 DNA Is Replicated Semiconservatively
13.4 Errors in DNA Can Be Repaired
13.5 The Polymerase Chain Reaction Amplifies DNA
Consistent
width of 2 nm
Figure 13.6
DNA Is a
Double
Helix 3.4 nm and
10 bp in
one full turn
Figure 13.7 Each DNA Strand Consists of a
Sugar–Phosphate Backbone
Concept 13.2 DNA Has a Structure That Suits Its
Function
• Purines – 2 rings
• Adenine (A)
• Guanine (G)
• Pyrimidines – 1 ring
• Cytosine (C)
• Thymine (T)
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How many turns in a double-stranded DNA molecule that
contains 10 000 bases.
(Reminder: 10 bp per full turn)
A. 500 turns
B. 1 000 turns
C. 5 000 turns
D. 10 000 turns
E. Cannot be determined
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How many turns in a double-stranded DNA molecule that
contains 10 000 bases.
(Reminder: 10 bp per full turn)
• 10 000 bases = 10 000 / 2 = 5 000 bp
• 10 bp in one turn, so 5 000 / 10 = 500 turns
If a sequence in one strand of DNA is 5ʹ-AGCTGCTGA-3ʹ,
what is the sequence in the complementary strand?
A. 5ʹ-AGCTGCTGA-3ʹ
B. 3ʹ-AGCTGCTGA-5ʹ
C. 5ʹ-TCGACGACT-3ʹ
D. 3ʹ-TCGATGACT-5ʹ
E. 5ʹ-TCAGCAGCT-3ʹ
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If a sequence in one strand of DNA is 5ʹ-AGCTGCTGA-3ʹ,
what is the sequence in the complementary strand?
A. 5ʹ-AGCTGCTGA-3ʹ
B. 3ʹ-AGCTGCTGA-5ʹ 5ʹ-AGCTGCTGA-3ʹ
C. 5ʹ-TCGACGACT-3ʹ 3’-TCGACGACT-5’
D. 3ʹ-TCGATGACT-5ʹ
E. 5ʹ-TCAGCAGCT-3ʹ
5’-TCAGCAGCT-3’
In this double-stranded DNA molecule, the 10 bases on one strand are:
5ʹ-AGCTGCTGAA-3ʹ
How many phosphodiester bonds would there be in this DNA molecule?
Rank Responses
1
2
3
4
5
6
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In this double-stranded DNA molecule, the 10 bases on one strand are:
5ʹ-AGCTGCTGAA-3ʹ
How many phosphodiester bonds would there be in this DNA molecule?
5ʹ-AGCTGCTGAA-3ʹ
5ʹ-A X G X C X T X G X C X T X G X A X A-3ʹ
(Bases – 1) = 9 per strand x 2 strands = 18 Bonds
In this double-stranded DNA molecule, the 10 bases on one strand are:
5ʹ-AGCTGCTGAA-3ʹ
How many hydrogen bonds would there be in this DNA molecule?
Rank Responses
1
2
3
4
5
6
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In this double-stranded DNA molecule, the 10 bases on one strand are:
5ʹ-AGCTGCTGAA-3ʹ
How many hydrogen bonds would there be in this DNA molecule?
5ʹ-AGCTGCTGAA-3ʹ
5ʹ - A G C T G C T G A A - 3ʹ
2 3 3 2 3 3 2 3 2 2 = 25
3ʹ - T C G A C G A C T T - 5ʹ
• Please complete this replication bubble by adding as
Homework many relevant labels as you can possibly do:
Chapter 13 DNA and Its Role in Heredity
Key Concepts
13.1 Experiments Revealed the Function of DNA as Genetic Material
13.2 DNA Has a Structure That Fits Its Function
13.3 DNA Is Replicated Semiconservatively
13.4 Errors in DNA Can Be Repaired
13.5 The Polymerase Chain Reaction Amplifies DNA
DNA
replication
models
Which of the following statements best describes the key distinction between the
three proposed models of DNA replication before Meselson and Stahl’s experiment?
A. The semiconservative model suggests that each daughter
DNA molecule consists of entirely new strands, while the
conservative model suggests that parental strands remain
together.
B. The dispersive model proposes that DNA replication occurs
randomly throughout the molecule, while the conservative
model proposes the original double helix is fully preserved.
C. The conservative model and dispersive model both suggest
that DNA strands are entirely new in the daughter molecules.
D. The semiconservative and dispersive models both propose
that newly synthesized DNA is evenly mixed with old DNA, but
the conservative model suggests completely new molecules
with the old DNA being lost.
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Meselson and Stahl: Which model is true?
15 N – 14 N – 14 N –
Heavy! Light! Light!
This is the results of size separation before the start of the
experiment. What does this tell you about the DNA in the cells?
A. The DNA molecules all are
heavy (15 N only)
B. The DNA molecules all are light
(14 N only) 14 N –
C. The DNA molecules are a Light!
mixture of light and heavy (15 N
and 14 N)
15 N –
Heavy!
Meselson and Stahl: Which model is true?
15 N – 14 N –
Heavy! Light!
This is the results of size separation after one round of
replication. What does this tell you about the DNA in the cells?
A. The DNA molecules all
are heavy (15 N only)
B. The DNA molecules all 14 N –
are light (14 N only) Light!
C. The DNA molecules are a
mixture of light and heavy
(15 N and 14 N) 15 N –
Heavy!
Which replication model(s) does this finding support?
A. Conservative
replication 14 N –
B. Semiconservative Light!
replication
C. Dispersive
replication 15 N –
Heavy!
Meselson and Stahl: Which model is true?
15 N – 14 N – 14 N –
Heavy! Light! Light!
This is the results of size separation after two rounds of
replication. What does this tell you about the DNA in the cells?
A. The DNA molecules all are
heavy (15 N only)
B. The DNA molecules all are light
(14 N only)
C. The DNA molecules are a
mixture of light and heavy (15 N
and 14 N)
Which replication model(s) does this finding support?
A. Semiconservative
replication
B. Dispersive
replication
Semiconservative model
In the Meselson and Stahl experiment, what result after two
generations of bacterial growth in 14N medium would have
supported the dispersive model of DNA replication?
A. Two bands, one at the density of 15N DNA and
another at 14N DNA.
B. A continuous gradient of DNA densities,
gradually shifting from 15N to 14N over
multiple generations.
C. A single band at an intermediate density
between 15N and 14N DNA.
D. Two bands, one at an intermediate density and
another at the density of 14N DNA.
Semiconservative DNA replication
DNA always consists of one old strand and one new strand.
That means that for replication, each strand of a double
helix is replicated in its entirety.
Figure 13.10
Figure 13.10
The incoming nucleotide shown here is cytosine. What will it
pair with, through which type of bond?
A. Pair with a C, through H-bonds.
B. Pair with a G, through H-bonds.
C. Pair with an A, through H-bonds
D. Pair with a T, through H-bonds
E. Pair with a C, through phosphodiester bonds.
F. Pair with a G, through phosphodiester bonds.
G. Pair with an A, through phosphodiester bonds.
H. Pair with a T, through phosphodiester bonds.
Figure 13.10
The incoming nucleotide shown here is a cytosine. It will be
added to the chain backbone through what type of bond,
and can be joined to which base?
A. H-bonds, joined to cytosine.
B. H-bonds, joined to guanine.
C. H-bonds, joined to any nucleotide.
D. Phosphodiester bonds, joined to cytosine.
E. Phosphodiester bonds, joined to guanine.
F. Phosphodiester bonds, joined to any base.
Figure 13.10
Figure 13.10
What drives the formation of the phosphodiester bond?
A. An enzyme
B. Energy from ATP
C. Energy from a triphosphate
D. Base-pairing
Figure 13.10
Therefore, to which end must the new nucleotide be added?
A. To a free 3’-OH group on the 3’ end
B. To a free 5’-OH group on the 5’ end
C. To a free 3’-phospate on the 5’ end
D. To a free 5’-phosphate on the 5’ end
E. It does not matter – a free 3’-OH group
or a free 5’-phosphate group
Figure 13.10
Which enzyme adds new nucleotides to the growing DNA
molecule?
A. RNA polymerase
B. DNA polymerase
C. Primase
D. Helicase
E. Ligase
F. Single stranded binding
proteins
Take-home message
Nucleotide polymers are always
added in the 5’ to 3’ direction (relative
to the new DNA strand) by making a
new phosphodiester bond through
linking an incoming 5’ P to a free 3’ OH
Take-home message
Nucleotide polymers are always
added in the 5’ to 3’ direction (relative
to the new DNA strand) by making a
new phosphodiester bond through
linking an incoming 5’ P to a free 3’ OH
Lessons learned
• DNA is made 5’ to 3’ through a phophodiester bond
• The energy for this reaction is provided by a tri-phosphate
on the incoming nucleotide
• New H-bonds are formed in the center of the double
helix
• This allows correct pairing maintaining the antiparallel
orientation of DNA
• A polymerase is used to make new nucleotide chains
• DNA polymerase for DNA replication
• Please complete this replication bubble by adding as
Homework many relevant labels as you can possibly do:
