Nucleic acids unit-5 D.Pharm 2nd year, biochemistry and clinical pathology. Definition, purine and pyrimidine bases Components of nucleosides and nucleotides with examples Structure of DNA (Watson and Crick model), RNA and their functions

1. Branch -Pharmacy
Biochemistry and Clinical Pathology
(ER20-23T)
Nucleic acids
• Definition, purine and
pyrimidine bases
• Components of nucleosides
and nucleotides with
examples
• Structure of DNA (Watson
and Crick model), RNA and
their functions

3. Nucleic acid
Nucleic acids (DNA and RNA) are formed by the
polymerisation of nucleotide subunits. Nucleotides are
made up of a ribose sugar, a nitrogenous base, and
phosphate group(s). Deoxyribonucleic Acid (DNA) and
Ribonucleic Acid (RNA) are the two types of nucleic
acids that act as sources and carriers of genetic
information.
Johann Friedrich Miescher (a Swiss researcher)
discovered DNA in 1869. In the year 1944, three
scholars Avery, Macleod, and MacCarty first
demonstrated that DNA carries genetic information.

4. FUNCTIONS OF NUCLEIC ACID
1. DNA is required for replication and heredity.
2. It is reserve bank of genetic information
3. They are responsible for maintaining the identity of
different species of organisms overmillions of years
4. Various cellular function is under the control of DNA
5. They take part in protein synthesis from RNA in body.
6. Nucleotides are precursors of the nucleic acids,
deoxyribonucleic acid (DNA) and ribonucleic acid
(RNA).
7. The nucleic acids are concerned with the storage and
transfer of genetic information.

12. PURINE BASES PRESENT IN THE
PLANTS-
Plants contains certain methylated proteins-
 Caffeine (1,3,7-trimethylxanthine-2,6-dioxypurine). It is
found in coffee. It acts as a stimulant.
 Theophylline (1.3-dimethylxanthine 2,6-dioxypurine) which
is present in tea leaves. It acts as bronchial smooth muscle
relaxant.

13. PYRIMIDINES
There are minor pyrimidines are also present in nucleic acids and also
minor & unusual bases are often found in DNA & RNA. These include
methyl cytosine present in DNA & dihydrouracil(used in the treatment of
cancer) present in tRNA.
1. Modification of Cytosine is
a) 5-methylcytosine
b) 5-hydroxymethylcytosine
2. Modification of Uracil is
a) Dihydroxyuracil
PHOSPHATE
Phosphate groups esterified to the sugar.
1. When a base combines with a pentose sugar, a nucleoside is formed.
2. When the nucleoside is esterified to a phosphate group, it is called a
nucleotide or nucleoside monophosphate.

17. FUNCTION OF NUCLEOTIDES
1.It is important components of nucleic acids (which are long chains of
nucleotides).
2. Source of ATP (Adenosine TriPhosphate) which is central to energy
metabolism.
3. Source of GTP (Guanosine Tri Phosphate) which drives protein synthesis.
4. Source of CTP (Cytidine Tri Phosphate) which drives lipid synthesis.
5. Source of UTP (Uridine Tri Phosphate) which drives carbohydrate
Metabolism.
6. It plays an important role for energy transport coenzymes (NAD+, NADP+,
and FAD+).
7. It play an important role for chemical intracellular messengers (e.g., Cyclic
AMP, a cyclic nucleotide that carries messages from the cell membrane to
molecules within the cell, to stimulate essential reactions and regulators of
cellular metabolism and reproduction)

19. For purine- sine
For pyrimidine- idine

25. Phosphate groups –hydrophilic
Bases- Hydrophobic

31. The model having following characteristics.
1. DNA structure is the well-known double helix formed by Watson-Crick base-pairing of C with G and A with T.
2. This is known as B-form DNA, and is the most favourable and common state of DNA;
3. Its highly specific and stable base-pairing is the basis of reliable genetic information storage.
4. Double helical structure of DNA was proposed by Watson & Crick in 1953. The DNA is a right handed double
helix.
5. It consists of two polydeoxyribonucleotide chains twisted around each other on a common axis of symmetry.
6. The chains are paired in an antiparallel manner, that is, the 5'-end of one strand is paired with the 3'-end of the
other strand. The two strands are antiparallel, i.e., one strand runs in the 5' to 3' direction while the other runs in 3' to
5' direction. The width (or diameter)of a double helix is 20A° (2 nm).
7. Each turn of helix is 34 Aº (3.4 nm) with 10 pairs of nucleotides, each pair placed at a distance of about 3.4 Aº.
8. The DNA helix, the hydrophilic deoxyribose-phosphate backbone of each chain is on the outside of the molecule,
whereas the hydrophobic bases are stacked inside.
9. The polynucleotide chains are not identical but complementary to each other due to base pairing.
10. The two strands are held together by hydrogen bonds. A=T,G≡C. The hydrogen bonds are formed between a
purine & pyrimidine.
11. The spatial relationship between the two strands in the helix creates a major (wide)groove and a minor (narrow)
groove.
12. These grooves provide access for the binding of regulatory proteins to their specific recognition sequences along
the DNA chain. DNA helix proves Chargaff's.
13. The genetic information resides on one of the two strands known as template strand or sense strand.
14. The opposite strand is antisense strand.
THE DNA DOUBLE HELIX

37. FUNCTIONS OF DNA
1. It plays an important role for store of genetic information.
2. Genetic information is the source of information for the synthesis
of all protein molecules.
3. The information is copied or transcribed into RNA molecules.
4. Proteins are then synthesized in the process involving the
translation of the RNA
5. DNA provides the inherited information by the daughter cell.
DNA provide template for the replication of information into
daughter DNA molecule.
6. DNA's role as genetic material and an understanding of its
chemistry allows us to manipulate to enhance quality of life.
7. These are also known as the building blocks of proteins.
8. DNA is required for coding of proteins.

39. RNA
Like proteins, the structure of RNA can also be divided into
primary, secondary, tertiary and quaternary structures:
1) The primary structure of RNA includes sequencing of bases
within RNA molecules.
2) The secondary structure of RNA consists of helical regions and
various kinds of bulges, loops, and junctions within the helical
regions. This region is stabilised by Watson-Crick base pairing.
3) The tertiary structure includes the arrangement of these
secondary structures into a 3D structure. These three structures are
often compact and stabilised by metal cations. The tertiary structure
includes pseudo-knots and high order tertiary interactions.
4) The quaternary structure includes the arrangement of RNA
strand with respect to other RNA strands or with protein molecules.

41. FUNCTIONS OF RNA
1) Ribonucleic acid (RNA) functions in converting genetic information from genes into
the amino acid sequences of proteins.
2) RNA translates the DNA message to a format that can be read by ribosomes, or the
cellular organelles that assemble proteins (process known as translation).
3) RNA also plays a role in engage the correct amino acids to the protein meeting sites.
4) RNA differs from DNA in that it is a single strand does not contain regions of double
helical structure.
5) Messenger RNA provides a template for protein synthesis by ribosome with a sequence
of amino acids corresponding to the sequence stored in DNA.
6) Transfer RNA brings amino acids from the mRNA to the ribosome.
7) They make up ribosome to assemble proteins.
8) Ribosomal RNA associates with a set of proteins to form ribosomes.
9) Synthesis of RNA is usually catalyzed by an enzyme RNA polymerase using DNA as a
template a process known as transcription.
10) RNA is the transfer of genetic information from the nucleus to the cells.

42. MULTIPLE CHOICE QUESTIONS
1. RNA is-
a. Double strand b. single strand
c. . Tetra strand. d. None of these
2. DNA is-
a. Double strand b. single strand
c. Tetra strand d. None of these
3. RNA does not consists of
a. Adenine b. Guanine
c. Thymine d. Aliphatic
4 The combination of a base and sugar is called
a. Adenine b. ribosomes
c. Nucleotides d. Nucleosides
5. Double helical structure of DNA was proposed by
a Watson & Crick b Watson
c Crick d Tswett

43. QUESTIONS
1. What is nucleotide
2. What is nucleoside
3. What is nucleic acid
4. What are nitrogenous bases
5. What is the difference between DNA and RNA
6. Discuss the structure and function of DNA
7. Discuss the structure and function of RNA
8. Explain the differences between nucleotides and
nucleosides