Chapter 27 Nucleosides, Nucleotides, and Nucleic Acids I Irene Lee Case Western Reserve University...
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Chapter 27 Nucleosides, Nucleotides, and Nucleic Acids I Irene Lee Case Western Reserve University Cleveland, OH ©2004, Prentice Hall Organic Chemistry 4 th Edition Paula Yurkanis Bruice
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Transcript of Chapter 27 Nucleosides, Nucleotides, and Nucleic Acids I Irene Lee Case Western Reserve University...
Chapter 27
Nucleosides,Nucleotides,
and Nucleic Acids I
Irene LeeCase Western Reserve University
Cleveland, OH©2004, Prentice Hall
Organic Chemistry 4th Edition
Paula Yurkanis Bruice
Nucleic Acids
In nucleic acid, the phosphate group is phosphodiester
The Bases in Nucleic Acids
Adenine, guanine, cytosine, and thymine are found in DNA
Adenine, guanine, cytosine, and uracil are found in RNA
Nucleosides = Base + Sugar
Nucleotides = Base + Sugar + Phosphate
Different Forms of Nucleotides
The energy released from ATP hydrolysis is used to drivethe phosphorylation of D-gluose (coupled reactions)
ATP as a Chemical Energy Source
Breakage of the Phosphoanhydride Bond in ATP
Without ATP, the OH– group cannot be displaced
This reaction does not occur without ATP because of the poor leaving group
Phosphoryl Transfer Reaction Mechanism I
Phosphoryl Transfer Reaction Mechanism II
Phosphoryl Transfer Mechanism III
P
O
-O O-O P
O
O-O-
+ H2O P
O
-OO-
OH2
Pyrophosphate can be further hydrolyzed to phosphate
Why is the hydrolysis of a phosphoanhydride bond soexergonic?
1. Greater electrostatic repulsion in ATP
2. More solvation in the products
3. Greater resonance stabilization in the products
P
O
-O O-O P
O
O-
P
O
-OO-
P
O
-OO-
OH
+
The interactions between ATP, Mg2+, and arginine and lysine residues at the active site of an enzyme
Since all the negative charges in ATP are neutralized, ATP is readily approached by nucleophiles
Other Important Nucleotides
Cyclic AMP serves as a link between several hormonesand certain enzymes that regulate cellular function
The Nucleic Acids
Biosynthesis of DNAoccurs in the 5’ 3’direction
Complementary Base Pairing in DNA
The sugar–phosphate is on the outside, and the basesare on the inside
The DNA Double Helix
Hydrolysis of RNA
The Three Helical Forms of DNA
Hydrogen bonding and base stacking interactions hold the DNA helix together
Replication of DNA
Transcription of DNA
• A stretch of bases representing a portion of a gene is called an exon
• A stretch of bases that contain no genetic information is called an intron
• mRNA is spliced prior to leaving the nucleus
A Transfer RNA
The Proposed Mechanism for Aminoacyl-tRNA Synthetase
The Substrate-Binding Site for tRNAHis
A protein is synthesized from its N-terminal end to itsC-terminal endEach amino acid is specified by a three-base sequenceknown as the genetic code
Translation
Why does DNA contain thymine instead of uracil?
The synthesis of thymine is energetically expensive
Because cytosine can be converted to uracil ….
Having T’s in place of U’s in DNA allows the U’s that arefound in DNA to be recognized as mistakes
DNA Sequencing
Laboratory Synthesis of DNA
OligonucleotideSynthesis with
Phosphoramidites
The amino groups of the bases must be protected
Removal of the Protecting Group by Ammonia
Utilization of H-phosphatemonomer to synthesize DNA strand
Hoogsteen Base Pairing
