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