This document discusses nucleotides, nucleosides, nucleic acids, and their structures and functions. Some key points: - Nucleotides are composed of a nitrogenous base, sugar (ribose or deoxyribose), and phosphate. Nucleosides lack the phosphate. - Purine nucleosides contain adenine or guanine, while pyrimidine nucleosides contain cytosine, uracil, or thymine. - Nucleotides and nucleosides play important roles in cell signaling, energy storage, and as components of nucleic acids and coenzymes. - Nucleic acids DNA and RNA are polymers of nucleotides. DNA has the sugar deoxyrib

1. NUCLEOTIDES, NUCLEOSIDE AND
NUCLEIC ACIDS

2. NUCLEOSIDE
A nucleoside is composed of purine and pyrimidine
base and sugar.
 Nucleosides are classified based on the nitrogneous
base present as purine nucleosides or pyrimidine
nucleosides
In the case of purine nucleosides, the sugar is
attached to N-9 of purine ring where as in pyrimidine
nucleosides the sugar is attached to N-1 of pyrimidine
ring.
The type of linkage is N-glycosidic and sugar can be
ribose or deoxyribose.

3. PURINE NUCLEOSIDE
 They contain purine bases adenine and guanine.
 Adenosine is nucleoside of adenine and guanosine is the nucleoside of
guanine.
If adenine is linked to deoxyribose then it is named as deoxy adenosine
Adenosine = Adenine+Ribose
Guanosine = Guanine+Ribose

4. UNUSUAL NUCLEOSIDES
 Ribothymidine and pseudouridine are examples of unusual
nucleosides.
 Ribothymidine consist of thymine and ribose. It is present in
ribonucleic acids (RNA) which is not usually found.
 Pseudouridine is an unusual nucleoside of uracil.
 In this nucleoside carbon–carbon bonding occurs between
uracil and ribose instead of the carbon –nitrogen bond.

5. Pyrimidine nucleosides
 These nucleosides are composed of pyrimidine bases.
 Cytosine, Uracil and thymine are pyrimidine nitrogenous bases.
 Cytidine is nucleoside of cytosine.
Uridine and thymidine are nucleosides of uracil and thymine
respectively.
Cytidine = Cytosine + Ribose
Uridine = Uracil + Ribose
Thymidine = Thymine+ Ribose

6. NUCLEOTIDES
 They are phosphorylated nucleosides.
 A nucleotide consist of nitrogenous base, sugar and phosphate.
Nucleotide = Purine or Pyrimidine base + Sugar + Phosphate

7. IMPORTANT BIOLOGICAL FUNCTIONS OF NUCLEOTIDES
AND NUCLEOSIDES.
1. Nucleotides are involved in signal transduction.
2. Nucleotides are required for the formation of nucleic acids.
3. Nucleotides are high energy compounds.
4. Nucleotides are components of some water soluble vitamin
coenzymes.
5. Nucleotides serve as second messengers. Many hormones
mediate their action through second messengers.
6. Some nucleotides function as donors of sugars, nitrogenous
compounds and phosphates.
7. Nucleosides function as carriers or donors of groups.
8. Nucleoside analogs are used as anti cancer agents.
9. Some nucleotides function as alarmones. They alarm cell when
something goes wrong in the cell.

8. Synthetic analogs of purines, pyrimidines and nucleosides
 Some synthetic purine and pyrimidine analogs are used as anticancer
agents and antiviral gents.
 Purine analogs are mercaptopurine, thioguanine, aminopurine etc.
 Pyrimidine analog is 5- fluro uracil.
 Nucleoside analogs are used as anticancer agents, antiviral agents
and mutagens.
 Deazauridine, 6-aza uridine, ara-A, ara-C and fluro deoxyuridine are
nucleoside analogs used as anticancer agents.
 Azidothymidine(AZT), dideoxy cytidine and iododeoxyuridine are
used as anti viral agents.
 Bromodeoxy uridine is used as mutagen.

9. Pharmacologically important purines
Caffeine of coffee, theophylline of tea and theobromine of tea are
some purines of pharmacological importance.
 Caffeine and theophylline act as CNS stimulants.
 Inhalers used by asthma patients contains theophylline. It releives
nasal and bronchial congestion of these patients.

10. Nucleotides of biochemical ( Physiological) importance
 Cells present in various organs of human body and other mammals
contain several free nucleotides.
These free nucleotides are involved in many biochemical or biological
processess

11. Adenine nucleotides and their physiological importance
1. Adenosine triphosphate (ATP), adenosine diphosphate (ADP) and
adenosine
monophosphate (AMP) are most important adenine nucleotides.
2. ATP, ADP, and AMP are high energy compounds.
3. ATP is popularly called as 'energy currency' of cell. Energy
exchange in biochemical reactions occurs through ATP.
4. ADP is required for the formation of ATP in electron transport
chain and in energy yielding reactions.
5. cAMP, a cyclic nucleotide of adenine is known as second
messenger. Many hormones action occurs through cAMP.
6. Many coenzymes of water soluble vitamins contain adenine
nucleotides. For example NAD, FAD, NADP, coenzyme A and
cobamide coenzymes.

12. 7. PAPS (Phospho adenosine phosphosulfate) serve as donor of
sulfate in biosynthetic reactions.
8. ATP is required for replication and protein biosynthesis.
9. Some adenosine nucleotides are involved in blood pressure
and platelet function.
10 Diadenosine nucleotides are neurotransmitters.
11. Oligoadenylate mediates action of interferon.
12. Poly adenylate serve as tail of mRNA

13. Guanine nucleotides and their physiological importance
1. Like ATP, ADP; Guanosine triphosphate (GTP) and guanosine
diphosphate (GDP) also exist in cells.
2. GTP and GDP are high energy compounds.
3. Cyclic GMP or cGMP mediates actions of several hormones.
4. GTP and GDP are components of G-proteins which are involved
in signal transduction
of several physiological processes like taste, odor, vision, metabolic
regulation etc.
5. GTP is required for replication and protein biosynthesis.
6. Guanine nucleotides are required for catalytic function of
ribonucleic acids or ribozymes.
7. Mucopolysacharide formation requires guanine nucleotides.

14. Cytosine nucleotides of physiological importance
1. CTP (Cytidine triphosphate), CDP (Cytidine diphosphate) and
CMP(Cytidine monophsphate), are high energy compounds.
2. Cyclic CMP or cCMP also occurs in cells.
3. CDP, CMP serve as donor of nitrogenous compounds during
biosynthesis.
4. CMP-NANA serve as donor of NANA in the biosynthesis of
gangliosides.
5. CDP- choline serve as donor of choline in phospholipids
biosynthesis.

15. Uracil nucleotides of physiological importance
1. UTP(Uridine triphosphate), UDP (Uridine diphosphate) and
UMP (Uridine monophosphate) are high energy compounds.
2. UDP- Glucuronic acid serve as donor of glucuronic acid in the
synthesis of mucopolysacharides, bilirubin diglucuronide and
detoxification reactions.
3. UDP is carner of sugar and aminosugars needed for synthesis
of glycogen, gangliosides, glycoproteins etc.

16. Thymine nucleotides of physiological importance
1. TTP(thymidine triphosphate), TDP(thymidine diphosphate) and
TMP( thymidine monophosphate) are high energy compounds.
2. TTP and d TTP are used for the synthesis of nucleic acids.

17. Hypoxanthine and xanthine
These are purine bases not found in nucleic acids. But their nucleotides have
important role in metabolism.
1. IDP (inosine diphosphate), IMP (inosine monophosphate) are nucleotides of
hypoxanthine. They are high energy compounds.
2. IMP is intermediate in purine nucleotide biosynthesis.
3. XMP (xanthosine monophosphate) is an intermediate in purine nucleotide
biosynthesis.

18. NUCLEIC ACIDS
 Two types of nucleic acids are found in cells. They are deoxy
ribonucleic acid (DNA) and ribonucleic acid (RNA).
 Pentose sugar in DNA is deoxyribose where as in RNA it is ribose.
 Due to deoxyribose nucleotides present in DNA are known as
deoxy ribonucleotides. They are designated as dADP, dATP; dGDP,
dGTP, dTTP, dTDP, dCTP, dCDP etc.
 Both DNA and RNA are polymers of nucleotides and often
referred as polynucleotides.

19. DNA structure
1. It consist of two polynucleotide chains.
2. These polynucleotide chains coil along long axis in the form
double helix.
3. Each polynucleotide is made up of four types of nucleotides.
4. Individual nucleotides are joined by phosphodiester bonds.
5. Four types of nucleotides are present in two chains. They are
adenylicacid, guanylic acid, cytidylic acid and thymidylic acid.
6. Each polynucleotide chain or strand has direction or polarity
and 5‘ and 3'ends.
7. These ends may be in either free form or phosphorylated
form.

20. 8. The two strands are complementary to each other.
9. Base composition of a strand is complementary to opposite
strand. If thymine is found in one strand adenine appears in
opposite strand and vice versa. Like wise if guanine appears in one
strand cytosine is found in opposite strand and vice versa.
10. Further bases of opposite strands are involved in pairing. It is
popularly known as base pairing rule. Adenine of one strand pairs
with thymine of opposite strand through two hydrogen bonds.
Guanine of a strand pairs with cytosine of opposite strand through
three hydrogen bonds.

21. DNA double helix
one
helical
turn
34 Å
major
groove
12 Å
minor
groove
6 Å
backbone: deoxyribose and phosphodiester linkage
bases

22. 11. Due to the presence of three hydrogen bonds GC pair is
stronger than AT pair.
12. This base pairing makes copying mechanism simple and
easier.
13. Complementary nature of two strands and base pairing rule
are most outstanding features of Watson-Crick model.
14. The base pairs are stacked. The pitch of the helix is 34 A and
contain ten base pairs. The width of the helix is 20 A .
15. Due to the presence of hydrogen bonds throughout the
molecule DNA is highly stable.
16. Major and minor grooves are present on the double helix.
17. Watson- Crick model DNA is known as B-DNA.

23. Functions DNA
1. DNA is genetic material of living organisms. It contains all the information
needed for the development of entire organism or individual.
2. DNA is transferred from parent to the offspring or generation to
generation.
3. DNA contains information required for formation of individuals proteins.
4. Information is present in DNA in the form of genes.
5. Amount of DNA present in the cell of an organism depends on complexity
of organisms.
6. Human cells contain more DNA than bacterial cells or viruses.
7. DNA amount in given cell is independent of nutritional or metabolic state
of the organism.
8. DNA flows from generation to generation in any given species.
9. DNA determines physical fitness of an organism or susceptibility to disease.

24. RNA
There are three types of RNAs in cells. They are present in prokaryotes
as well as eukaryotes.
They are
(1). Messenger RNA or mRNA
(2). Transfer RNA or tRNA
(3). Ribosomal RNA or rRNA.

25. MESSENGER RNA
1. Majority of mRNA molecules are linear polymers.
2. They contain about 1000-10, 000 nucleotides.
3. They have 3' or 5' free or phosphorylated ends
4. Life span of m RNA molecules varies from few minutes to days.
5. Some RNAs have secondary structure.
6. Intra strand base pairing among complementary bases leads to
folding of linear molecules
into hair pin like secondary structure.
7. In some m RNA at 5'and 3' ends special nucleotides or sequences
occurs.
8. Poly A tail is present in some mRNAs at 3' end.
9. At 5' end some mRNA are capped. Methylated GTP is cap.
10. At 5' and an AG rich shine – Dalgarno sequence is present in
some mRNAs

26. Functions
1. mRNA carries genetic information from nucleus to cytoplasm.
2. Generally one mRNA contains information for formation one
protein.
3. The sequence of mRNA is complementary to strand from which it is
copied.
4. In mRNA genetic information is present in the form of genetic
code.
5. Occasionally one mRNA contains information for the formation of
more than one protein.

27. Transfer RNA (tRNA)
 It is smallest of all RNAs and contains up to 100 nucleotides.
 It contains several unusual bases like pseudouridine, dihydro
uracil, mythylated adenine and guanine and isopentenyl adenine etc.
 Due to intra strand base pairing between complementary bases
tRNA molecules exist in characteristic secondary structure shape.
 Secondary structure of tRNAs is in the form of clover leaf.

28. Structural features of tRNA
1. It contains an aminoacid arm at 3' end CCA is characteristic sequence of
aminoacid arm.
2. An arm containing unusual pseudouridine and ribothymidine. Hence it is
known as TφC arm
in which pseudouridine is indicated with psi ( φ ) symbol.
3. An anticodon arm containing IGC sequence. Generally this arm recognizes
codon on mRNA.
4. Dihydrouridine (UH ) arm or DHU arm that contains dihydrouracil.
5. A guanine containing 5'end.

29. Functions
1. It serve as adaptor molecule in protein biosynthesis. It carries amino
acids to site of protein synthesis.
2. For every aminoacid one specific tRNA molecule exist.
3. Stability of eukaryotic and prokaryotic tRNA varies.

30. Ribosomal RNA ( rRNA)
 It is found in combination with proteins in ribosomes. It contains about 100-600
nucleotides.
 Prokaryotic and eukaryotic ribosomes contain several RNA that differ in
sedimentation coefficient.
 Due to intra strand base pairing between complementary bases secondary
structures are found in rRNA molecules.
They are known as domains. 16S rRNA with 1500 nucleotides has
four major domains.

31. Functions
1. It is involved in initiation of protein synthesis.
2. It is required for the formation of ribosomes.

32. Differences between DNA and RNA
• DNA
1. Double stranded molecule
2. Found in combination with proteins.
3. Pentose sugar is deoxyribose.
4. Sum of the purine bases is equal to
sum of pyrimidine bases. A+G=C+T
5. Pyrimidine base uracil is absent.
6. Only one form of DNA
predominantly occurs.
7. Resistant to alkaline hydrolysis.
8. Modified bases are usually absent.
9. Lacks catalytic activity.
• RNA
1. Single stranded molecule.
2. Except rRNA other RNAs exist as free
molecules
3. Pentose sugar is ribose.
4. Sum of purine bases is not equal to sum
of pyrimidine bases.
5. Thymine a pyrimidine base is not usually
found.
6. More than three types of RNAs occurs.
7. Easily hydrolyzed by alkali.
8. Unusual and modified bases are found.
9. Some RNAs act as enzymes or posses
catalytic
activity