Download 10.5 DNA replication

10.2 DNA and RNA are polymers of nucleotides
• DNA is a nucleic acid, made of long chains of
nucleotides
Phosphate
group
Nitrogenous
base
Sugar
Phosphate
group
Nitrogenous base
(A, G, C, or T)
Nucleotide
Thymine (T)
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate backbone
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Figure 10.2A
• DNA has four kinds of bases, A, T, C, and G
Thymine (T)
Cytosine (C)
Pyrimidines
Adenine (A)
Guanine (G)
Purines
Figure 10.2B
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• RNA is also a nucleic acid
– RNA has a slightly different sugar
– RNA has U instead of T
Nitrogenous base
(A, G, C, or U)
Phosphate
group
Uracil (U)
Sugar
(ribose)
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Figure 10.2C, D
10.3 DNA is a double-stranded helix
• James Watson and Francis Crick worked out
the three-dimensional structure of DNA, based
on work by Rosalind Franklin
Figure 10.3A, B
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• The structure of DNA consists of two
polynucleotide strands wrapped around each
other in a double helix
1 chocolate coat,
Blind (PRA)
Twist
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Figure 10.3C
• Hydrogen bonds between bases hold the
strands together
– Each base pairs with a complementary partner
– A pairs with T
– G pairs with C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Three representations of DNA
Hydrogen bond
Ribbon model
Partial chemical structure
Computer model
Figure 10.3D
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DNA REPLICATION
10.4 DNA replication depends on specific base
pairing
• In DNA replication, the strands separate
– Enzymes use each strand as a template to
assemble the new strands
A
Nucleotides
Parental molecule
of DNA
Both parental strands serve
as templates
Two identical daughter
molecules of DNA
Figure 10.4A
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• Untwisting and replication of DNA
Figure 10.4B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10.5 DNA replication: A closer look
• DNA replication begins at specific sites
Origin of replication
Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
Figure 10.5A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Each strand of the
double helix is
oriented in the
opposite direction
5 end
3 end
P
P
P
P
P
P
P
P
Figure 10.5B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
3 end
5 end
• How DNA
daughter
strands are
synthesized
• The
daughter
strands are
identical to
the parent
molecule
DNA polymerase
molecule
5 end
Daughter strand
synthesized
continuously
Parental DNA
5
3
Daughter
strand
synthesized
in pieces
3
5
P
5
3
P
DNA ligase
Overall direction of replication
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
3
5
Figure 10.5C