1. BIOCHEMISTRY OF NUCLEIC ACIDS
GATLUAK JAMES KEDOK JIEK JANY

2. Learning Objectives
A) Introduction
B) Classification
C) Chemical Nature
D) Biological Role

3. A) Introduction
Friedrich Miescher who discovered nucleic acids in 1871
Nucleid acids are polymers that consists of nucleotide residues.
Located in nucleic of cell.
Hereditary determinants of living organisms.
Elemental comosition – carbon, hydrogen, oxygen, nitrogen and phosphorus.

4. B) Classification/Types of Nucleic Acids
1. Deoxyribonucleic Acid (DNA)
2. Ribonucleic Acid (RNA)
Central Dogma of Life
DNA  RNA  Protein
DNA to DNA = Replication
DNA to RNA = Transcription
RNA to Protein = Translation
1. Deoxyribonucleic Acid (DNA)
Function: storage of genetic material.
2. Ribonucleic Acid (RNA)
> Function: to transfer genetic information from nucleus to cytoplasm fro protein
synthesis. There are 3 types of RNA:

5. a) Messenger RNA (mRNA)
Function: It is a complementary copy of selected region of the DNA. It carries the
genetic message from the nucleus to the cytoplasm and acts as the template for
protein synthesis.
b) Ribosomal RNA (rRNA)
Function: rRNA along with proteins forms the ribosomes which is the site of
enzyme synthesis. Some of them have catalytic and coenzyme functions as well.
c) Transfer RNA (tRNA)
Function: Transfer the amino acids to the site of protein synthesis.

6. Properties of Nucleic Acids
Nucleic acids are soluble in alcohol, slightly soluble in cold water, but readily
dissolve in hot water and dilute alkalis, forming alkali salts. They are precipitated
by HCL and by excess of acetic acid.
Feulgen test differentiates the DNA from RNA, if the deoxyribose sugar is present,
a red colour is produced with the dye. Ribose sugars do not exhibit this reaction.

7. Chemical Nature of Nucleic Acid
Nucleic Acid Structure or Composition of Nucleic Acid:
Nucleic acids are polynucleotides.
Their building blocks are nucleotides.
Nucleic acids are polymers of nucleotides.
Nucleotides are made up of Phosphate and Nucleosides.
Nucleosides are made up of Sugar and Bases.
Bases constitute Purines and Pyrimidines.
Sugar constitutes Ribose and Deoxyribose.

8. Nucleotides
Hydrolysis of nucleic acids gives nucleotide, which can be considered the units that make
up the polymer. Phosphate esters of nucleotides. A nucleotide consists of three parts:
1. Heterocyclic base
2. Sugar
3. Phosphoric Acids
Nucleotide = nucleoside + phosphate
When ribose or 2- deoxyribose is combined with purine or pyrimidine base, Nucleoside
is formed.
NUCLEOTIDE:
1. Phospahte.
2. Sugar (Ribose or Deoxyribose).
3. Base (a) Purines [Adenine(A), Guanine(G)] (b) Pyrimidines [Cytosine(C), Thymine(T),
Uracil(U).

9. Phosphoric Acid
Molecular formula H₃PO₄
Contains 3 noncovalent hydroxyl group and a divalent oxygen atom.
All linked to pentavalent phosphorous atom.
Sugar
The sugar in nucleotide, and so in nucleotide acids, is a Pentose.
In RNA = nucleotide, the sugar is Ribose.
In DNA = nucleotide, it is Deoxyribose.
The prefix deoxy – means without oxygen.

10. Heterocyclic or Nitrogen Bases
Present in nucleic acids are divided into two types- Purines and Pyrimidine.
The two purines present both DNA and RNA are adenine and guanine.
The Pyrimidines cytosine is present in both DNA and RNA, whereas thymine is found in
DNA only and Uracil is present in RNA only.
Pyrimidine
Six-membered heterocyclic ring containing 2 nitrogen atoms.
Two nitrogen atom at position 1 and 3
Three double bonds
Purines
Six-membered pyrimidine ring fused to five member imidazole ring.
Two nitrogen atom at position 1 and 3 in the pyrimidine ring and other two at position 7
and 9 in the imidazole ring.

11. Hydrolysis of Nucleic Acid Under Alkaline Condition
The covalent backbone of DNA and RNA is subject to slow non enzymatic hydrolysis of
the phosphodiester bond.
The experiment showed that in the test tube, RNA is hydrolyzed rapidly under alkaline
condition but DNA is not.
It has been found that the 2-hydroxyl group in RNA which is absent in DNA is ndirectly
involved in the process.
This explains that RNA is susceptible to alkaline attack but DNA is not.
Cyclic 2-3 monophosphate nucleotides are the first product of the reaction of alkali on
RNA and are rapidly hydrolyzed further to yield a mixture of 2- and 3- nucleotide
monophosphates.