BCH 4053 Biochemistry I
Fall 2001
Dr. Michael Blaber


Lecture 18

Nitrogenous bases, nucleosides, nucleotides, polynucleotides


Polymers of nucleic acids serve as the repository of genetic information in living systems

The "Central Dogma":

Nitrogenous Bases

Nitrogenous bases found in nucleic acids are derivatives of either pyrimidines or purines:

Common pyrimidines

Common purines

Properties of purines and pyrimidines

 

The Pentoses of Nucleotides and Nucleic Acids

Ribonucleic acids (RNA) and deoxyribonucleic acids (DNA) contain 5-carbon sugars (ribose) in addition to a purine or pyrimidine nitrogenous base

 

Nucleosides are Formed by Joining a Nitrogenous Base to a Ribose Sugar

A ribose and nitrogenous base are covalently joined by a glycosidic bond to form a nucleoside molecule:

Conformation of the nitrogenous bases in nucleoside molecules

 

Nucleotides are Nucleoside Phosphates

A nucleotide is formed when phosphoric acid is esterified to a sugar hydroxyl of a nucleoside

Summary of terms:

Base

Nucleoside

Nucleotide

RNA
(mono-Pi)

DNA
(mono-Pi)

Code

Adenine

(deoxy-)Adenosine

(deoxy-)Adenylic acid

AMP

dAMP

A

Guanine

(deoxy-)Guanosine

(deoxy-)Guanylic acid

GMP

dGMP

G

Cytosine

(deoxy-)Cytidine

(deoxy-)Cytidylic acid

CMP

dCMP

C

Thymine

Thymidine

Thymidylic acid

 

dTMP

T

Uracil

Uridine

Uridylic acid

UMP

 

U

 

Cyclic nucleotides

Nucleoside monophosphates can have two ester bonds to the phosphoric acid, and these can be within the same molecule via an ester bond to both the 5' and 3' hydroxyl groups of the ribose sugar:

 

Nucleoside diphosphates and triphosphates

Additional phosphoric acid groups can be linked to the existing phosphate in nucleotide monophosphates to produce di- and tri-phosphates.

 

Oligonucleotides are polymers of nucleic acids via 3'à 5' phosphodiester bonds

Oligonucleotides are synthesized by polymerase enzymes and NTP's or dNTP's

Shorthand for writing oligonucleotide sequences

 


© 2001 Dr. Michael Blaber