dna structure lecture
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dna structureTRANSCRIPT
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DNA STRUCTUREDNA STRUCTURE
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NUCLEIC ACIDSNUCLEIC ACIDS
Nucleic acids are polymersNucleic acids are polymers Monomer---nucleotidesMonomer---nucleotides
Nitrogenous basesNitrogenous bases PurinesPurines PyrimidinesPyrimidines
Sugar Sugar RiboseRibose DeoxyriboseDeoxyribose
PhosphatesPhosphates +nucleoside=nucleotide+nucleoside=nucleotide
}Nucleosides
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The Sugars The Sugars
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The Bases The Bases
PURINES
PYRIMIDINES
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Bases of DNA (and RNA)Bases of DNA (and RNA)Bases of DNA (and RNA)Bases of DNA (and RNA)
RNA only DNA only
Purines:
Pyrimidines:
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Nucleotides and Nucleotides and NucleosidesNucleosides
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Chemical Structure of DNA and RNA
Chemical Structure of DNA and RNA
Figure 4.1
RNA DNA
Nucleotide
Nucleoside
1’
2’
4’
The C is named 1’-5’
Resume
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Nucleotides and Nucleotides and NucleosidesNucleosides
BASEBASE NUCLEOSIDENUCLEOSIDE DEOXYNUCLEOSIDEOXYNUCLEOSIDEDE
AdenineAdenine AdenosineAdenosine 2-2-deoxyadenosinedeoxyadenosine
GuanineGuanine GuanosineGuanosine 2-2-deoxyguanosinedeoxyguanosine
CytosineCytosine CytodineCytodine 2-deoxycytodine2-deoxycytodine
UracilUracil UridineUridine Not usually found Not usually found
ThymineThymine Not usually foundNot usually found 2-deoxythymidine2-deoxythymidine
Nucleotides are nucleosides + phosphate
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make up 13-34% of the dry weight in bacteriadeoxyribonucleic acid (DNA) and ribonucleic acid (RNA)
O
C C
C C
Base
H
H or OH
H H
H
H
CH2OP
OH
O
HO
Nucleotide: a building block
Sugar:• RNA – ribose (OH)• DNA – deoxyribose (H)
Bases:• adenine (A), cytosine (C), guanine (G), thymine (T)• RNA uses uracil (U) instead of thymine
Nucleoside: base + sugar
• certain nucleotides serve as a storage of energy and reducing powere.g. ATP -> ADP -> AMP
hydrolysis (energy is released)
Nucleic Acids
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DNA Stabilization– DNA Stabilization– Complementary Base PairingComplementary Base Pairing
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DNA Stabilization-Base DNA Stabilization-Base StackingStacking
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DNA Stabilization--H-bonding DNA Stabilization--H-bonding between DNA base pair stacks between DNA base pair stacks
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Advantages to Double HelixAdvantages to Double Helix
Stability---protects bases from attack Stability---protects bases from attack by Hby H22O soluble compounds and HO soluble compounds and H22O O itself.itself.
Provides easy mechanism for Provides easy mechanism for replicationreplication
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G-C ContentG-C Content
A=T, G=C, but ATA=T, G=C, but AT≠GC≠GC Generally GC~50%, but extremely Generally GC~50%, but extremely
variablevariable EX.EX.
Slime mold~22%Slime mold~22% Mycobacterium~73%Mycobacterium~73%
Distribution of GC is not uniform in Distribution of GC is not uniform in genomesgenomes
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CONSEQUENCES OF GC CONSEQUENCES OF GC CONTENTCONTENT
GC slightly denser GC slightly denser Higher GC DNA moves further in a Higher GC DNA moves further in a
gradientgradient Higher # of base pairs=more stable Higher # of base pairs=more stable
DNA, i.e. the strands don’t separate DNA, i.e. the strands don’t separate as easily. as easily.
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FORMS OF DNAFORMS OF DNA
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Supercoiling Supercoiling
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RNA RNA
TypesTypes mRNAmRNA tRNAtRNA rRNArRNA
It’s still an RNA worldIt’s still an RNA world snRNAsnRNA siRNAsiRNA RibozymesRibozymes