dna and rna are large macromolecules with several levels of complexity nucleotides form the...
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• DNA and RNA are large macromolecules with several levels of complexity
• Nucleotides form the repeating units
• Phosphodiester bonds link nucleotides to form a strand
• Two strands interact to form a double helix
• The double helix interacts withproteins resulting in 3-D structuresin the form of chromatin
NUCLEIC ACID STRUCTURE
3D structure
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9-25Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or displayFigure 9.8
Nucleotide Components
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9-27Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
• Base + sugar nucleoside – Example
• Adenine + ribose = Adenosine• Adenine + deoxyribose = Deoxyadenosine
• Base + sugar + phosphate(s) nucleotide– Example
• Adenosine monophosphate (AMP)• Adenosine diphosphate (ADP)• Adenosine triphosphate (ATP)
Combining all the parts
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9-28Figure 9.10
Base always attached here
Phosphates are attached there
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Figure 9.9 The structure of nucleotides found in (a) DNA and (b) RNA
A, G, C or T A, G, C or U
dNMP NMP
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Nucleotide Polymerization Reaction: Phosphodiester Bond Formation
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9-30Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or displayFigure 9.11
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9-31Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
• 1953, James Watson and Francis Crick discovered the double helical structure of DNA
• The scientific framework for their breakthrough was provided by other scientists including– Linus Pauling– Rosalind Franklin– Erwin Chargaff
Events Leading to DNA Structure Determination
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Linus Pauling
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Rosalind Franklin• Helical• Double stranded• 10 base pairs per turn
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X-ray Diffraction Pattern of DNA
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9-35Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
• It was assumed the four bases: A, G, C and T were in a repeating, tetranucleotide configuration
• Therefore, there should be the same amount of A, G, C & T in any molecule of DNA form any source
• Chargaff carefully determined the exact percentages of nuceotides in DNA from several sources
Erwin Chargaff’s Experiment
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Erwin Chargaff’s Data
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• % A = % T & %G = %C• However %AT DID NOT = %GC• This observation became known as Chargaff’s rule
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Watson & Crick Model DNA Structure
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Base Pairing Key to DNA Structure
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Features of the DNA Double Helix
NH2
T
2 nm
One nucleotide0.34 nm
One completeturn 3.4 nm
O
O
HH
NN
H
H
HHOOO
OPO–
NH2
HN
N
NH
N
HH
H
OH
HHOOO
O–
PO–
HH
H
HHOOO
OPO–
NH2
O
O
H H
NN
H2N
HN
N
NH
N
H H
H
HHO
OOO–
PO
H H
H
HHO OO
O–
PO
H N
NH
N
N
H H
H
HHO
OOO–
PO–
H2N
HO5end 3end
3hydroxyl3end 5 end
5phosphate
TA
T A
T AP
PP
P
P
S
S
S
S
SS
S
S
A
C G
G
C G
C G
G
G
C
C
G C
GC
G C
C
P
PS
P
PP
P
P
S
SS
S
S
PP
P
P
PP
P
P
S
S SS
S
S
S
S
SP
S
S
P
PP
S
SS
SP
CH2
CH2
CH2
H2N
CH2
CH2
CH2
A
P
S
P
P
H
CH3H
NNHO
O
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Space-filling model of DNA
Ball-and-stick model of DNA
Minorgroove
Majorgroove
Minorgroove
Majorgroove
Features of the DNA Double Helix
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Major Helical Conformations of DNA
A-DNA B-DNA
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A26
0
Melting Point Curve: Tm is Proportional to %GC
Tm= 68.9 + (0.41)(%GC)
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The Three-Dimensional Structure of DNA
Figure 9.21
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• The primary structure of an RNA strand is much like that of a DNA strand
• RNA is made as a single strand only, however it may form a double stranded structures
• RNA strands can be a 10s to1000s of nt in length
• RNA is made from a DNA template - only one of the two strands of a DNA helix is used as the template
• RNA contains uracil rather than thymine
RNA Structure
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9-58Figure 9.22
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Figure 9.23
RNA Secondary Structures
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Figure 9.24
RNA Tertiary Structure – a tRNA
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