PyrimidinesPyrimidines& PurinesPurines

Pyrimidines and Purines

In order to understand the structureand properties of DNA and RNA, weneed to look at their structuralcomponents.

We begin with certain heterocyclicaromatic compounds called pyrimidinesand purines.

• Double helix,• Double strands,

DNADNA

…this structure was proposed in1953 by two Nobel prize winners:

The main role of DNA is the long-termstorage of genetic information (DNA asgenetic material)

RNA

Pyrimidines and PurinesPyrimidine and purine are the names ofthe parent compounds of two types ofnitrogen-containing heterocyclicaromatic compounds.

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NN

NN

NN

NN

NNHH

PyrimidinePyrimidine PurinePurine

Pyrimidines that occur in DNA arecytosine and thymine. Cytosine anduracil are the pyrimidines in RNA.

Important Pyrimidines

HHNN

NNHH

OO

OO

UracilUracil

HHNN

NNHH

OO

OO

CHCH33

ThymineThymine

HHNN

NNHH

NNHH22

OO

CytosineCytosine

Important PurinesAdenine and guanine are the principal

purines of both DNA and RNA.

AdenineAdenine

NN

NN

NNHH22

NN

NNHH

GuanineGuanine

OO

HHNN

NNHH

NN

NN

HH22NN

Caffeine and Theobromine

Caffeine (coffee) and theobromine (coffeeand tea) are naturally occurring purines.

CaffeineCaffeine

NN

NN

OO

NN

NN

HH33CC

OO

CHCH33

CHCH33

TheobromineTheobromine

OO

HHNN

NNNN

NN

CHCH33

CHCH33

OO

NucleosidesThe classical structural definition is that a

nucleoside is a pyrimidine or purine N-glycoside of D-ribofuranose or 2-deoxy-D-ribofuranose.

Informal use has extended this definition toapply to purine or pyrimidine N-glycosides ofalmost any carbohydrate.

The purine or pyrimidine part of a nucleosideis referred to as a purine or pyrimidine base.

Uridine and AdenosineUridine and adenosine are pyrimidine and purine

nucleosides respectively of D-ribofuranose.

UridineUridine(a (a pyrimidinepyrimidine nucleoside) nucleoside)

AdenosineAdenosine(a (a purinepurine nucleoside) nucleoside)

OO

NNHOCHHOCH22

HHNN

OO

OHOHHOHO

OO

NN NN

NN NNHOCHHOCH22 OO

OHOHHOHO

NNHH22

Nucleotides

They are phosphoric acid esters ofnucleosides.

Adenosine 5'-Monophosphate (AMP)

Adenosine 5'-monophosphate (AMP) isalso called 5'-adenylic acid.

NN NN

NN NN

OO

OHOHHOHO

NNHH22

OCHOCH22PPHOHO

OO

HOHO

Adenosine 5'-monophosphate (AMP) isalso called 5'-adenylic acid.

NN NN

NN NN

OO

OHOHHOHO

NNHH22

OCHOCH22PPHOHO

OO

HOHO1'1'

2'2'3'3'

4'4'5'5'

Adenosine 5'-Monophosphate (AMP)

Adenosine Diphosphate (ADP)

NN NN

NN NN

OO

OHOHHOHO

NNHH22

OCHOCH22PPOO

OO

HOHO

PP

OO

HOHO

HOHO

Adenosine Triphosphate (ATP)

NN NN

NN NN

OO

OHOHHOHO

NNHH22

OCHOCH22PPOO

OO

HOHO

PP

OO

HOHO

OOPP

OO

HOHO

HOHO

ATP Stores Energy

AMPAMP

ADPADP

ATPATP Each step is endothermic. Energy for each step comes

from carbohydrate metabolism(glycolysis).

Reverse process is exothermicand is the source of biologicalenergy.

ΔG° for hydrolysis of ATP toADP is –35 kJ/mol

Adenosine 3'-5'-CyclicMonophosphate (cAMP)

Cyclic AMP is an important regulatorof many biological processes.

NN NN

NN NN

OO

OHOHOO

NNHH22

CHCH22

PPOO

HOHO

OO

To be continuedTo be continued……