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dna structure
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DNA STRUCTUREDNA STRUCTURE
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
The Sugars The Sugars
The Bases The Bases
PURINES
PYRIMIDINES
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:
Nucleotides and Nucleotides and NucleosidesNucleosides
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
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
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
DNA Stabilization– DNA Stabilization– Complementary Base PairingComplementary Base Pairing
DNA Stabilization-Base DNA Stabilization-Base StackingStacking
DNA Stabilization--H-bonding DNA Stabilization--H-bonding between DNA base pair stacks between DNA base pair stacks
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
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
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.
FORMS OF DNAFORMS OF DNA
Supercoiling Supercoiling
RNA RNA
TypesTypes mRNAmRNA tRNAtRNA rRNArRNA
It’s still an RNA worldIt’s still an RNA world snRNAsnRNA siRNAsiRNA RibozymesRibozymes
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