2. Contents
Nucleic acids
DNA – introduction
Double helical model of DNA
Molecular structure of DNA
Nucleotides and nucleosides
features of DNA molecule
Types of DNA
Significance of DNA
4. Nucleic acid
1st
is0lated by fredrich miescher in 1868from nuclei of
cells and called it nuclein
Strong acids found in the nucleus hence their name.
also occurs in mitochondria and plasmid.
Giant macromolecules having complex structure and
composed of large no. of nucleotide molecules.
in a nucleic acid the phosphate component of one
nucleotide is joined to the sugar component of
another molecule by phosphodiester bond
5. DNA
DNA is the genetic material and forms the molecular
basis of heridity in all organisms. In certain viruses ,
such as tobacco mosaic virus RNA is the genetic
material .
In prokaryotes dna occurs in the cytoplasm but in
case of eukaryotes it is confined to the nucleus and
the main component of the chromosomes.
The DNA content is fairly constant in all the cells of a
given species
6. Structure of DNA
A polymer of deoxyribonucleotides
Double-stranded
INDIVIDUAL deoxynucleoside TRIPHOSPHATES ARE
COUPLED BY PHOSPHODIESTER BONDS
A “double helical” structure
Common axis for both helices
Right handed helix
Antiparallel relationship between 2 dna strands
7. DNA is a double-stranded helix
James Watson and Francis Crick worked out the three-
dimensional structure of DNA in the year 1952.
Figure 10.3A, B
9. Nucleotide
Nucleotides consists of
1)A pentose sugar (deoxy
ribose in case of DNA)
2)A nitrogenous base
Purines-
a)Adenine
b) Gaunine
Pyrimidines
a)Cytosine
b)Thymine
3) A phosphate group
10. Ribose and Deoxyribose sugar
Ribose sugar is present in RNA while Deoxyribose sugar is the characteristic
feature of DNA
11. Dna has 4 kind of bases
Pyrimidines
Thymine (T) Cytosine (C)
Purines
Adenine (A) Guanine (G)
12. Type of Nucleotides
Nucleotides are composed of – a pentose sugar,
aphosphate gp and a nitrogenous base.
There are four types of nucleotides in DNA
Adenosine monophosphate ( Adenyic acid )
Gaunosine mono phosphate(gaunilic acid)
Cytidine monophosphate ( cytidic acid)
Thymidine monophosphate (thymidic acid)
14. Molecular structure of DNA
The deoxyribose sugar of one nucleotide is joined to the
phosphate group of adjacent nucleotide with glycosidic
linkage to form a poly nucleotide chain
17. Features of DNA helix
Dna consists of helix in which two polynucleotide chains
and are coiled about same axis
Bases are set in a plane at a right angle to the long axis.
Two polypeptide chain which runs opposite directions
have complementary base pairing.
Distance between two base pairs is 3.4 A and since each
turn is about 34 A there are 10 pairs in each turn
18. STRUCTURE OF THE DOUBLE HELIX
4 MAJOR FORMS
B-DNA
A-DNA
C-DNA
Z-DNA
B-DNA IS BIOLOGICALLY THE MOST COMMON
RIGHT-HANDED (20 ANGSTROM (A) DIAMETER)
COMPLEMENTARY BASE-PAIRING (WATSON-
CRICK)
A-T
G-C
EACH BASE PAIR HAS ~ THE SAME WIDTH
10.85 A
19. Types of DNA
type A-DNA B-DNA C-DNA Z-DNA
Relative
humidity
75% 92% 66% Relativy low
humidity
Ionic
concentration
Na+ ,
K+,CS
+
Very low ionic
concentration
Presence of
lithum ion
Very high
ionic
concentrtion
Base pairs per
turn
12bp 10 bp 9.33 bp 11 bp
handed right right right left
Helix
diameter
25.5 2o 23 18.4
20. Significance of DNA
DNA is the blueprint that stores the information
needed to construct the components of cells in the
body.
DNA is the reserve bank of genatic information it
preserves the identity of a specie generation after
generation.
The apperance of an organism is determined by his
DNA.
21. Why Is DNA Important
The simplest answer for “Why Is DNA Important?” is
that DNA is the prerequisite for life’s inception. It
dictates life in two manners. Firstly, it transfers
hereditary information from generation to generation.
Secondly, it controls the production of proteins. DNA
even determines the structure of the cell, meaning
whether it would be a nerve cell or eye cell etc.
22. RNA
RNA molecules are also polynucleotides with a sugar-
phosphate backbone and four kinds of bases. The
main differences between RNA and DNA are:
RNA molecules are single-stranded
The sugar in RNA is a ribose sugar (as opposed to
deoxy-ribose) and has an OH at the 2' C position
highlighted in red in the figure below (DNA sugars
have H at that position)
Thymine in DNA is replaced by Uracil in RNA. T has
a methyl (-CH3) group instead of the H atom
25. Types of RNA
1. mRNA
Linear molecule.
Carries message (information) from DNA about the
sequence of a particular amino acid to be joined to
form a polypeptide.
Forms about 5% of the total rna of a cell
Its length is the largest of all types of rna.
Because the variation in size in mRNA population in a
cell it is also called hnRNA (hetrogenous nuclear
RNA)
Methylated cap & a poly A tail
27. 2.rRNA
It is greatly coiled in combination with protiens.
Forms a large and small subunits of ribosome.
Forms 80% of the total RNA
rRNAs are found within the large and small
ribosomal subunits.
A ribosome also has 3 binding sites called A, P, and E.
The A site in the ribosome binds to an aminoacyl-
tRNA (a tRNA bound to an amino acid).
28. The A site in the ribosome binds to an aminoacyl-
tRNA (a tRNA bound to an amino acid).
The amino (NH2) group of the aminoacyl-tRNA,
which contains the new amino acid, attacks the ester
linkage of peptidyl-tRNA (contained within the P
site), which contains the last amino acid of the
growing chain, forming a new peptide bond. This
reaction is catalyzed by peptidyl transferase.
30. 3. tRNA
Has many varieties each variety carries a specific
amino acid to the messanger rna on the ribosome to
form a polypepide.
It form 15% of the total rna of the rna of cell.
Its size is the smallest and it folds to assume a clover
leaf like structure.
Non-standard base pairing and other base-base
interactions.
Secondary & tertiary folding.
Intercalation & Mg2+
binding.
31.
32. Significance of RNA
The most essential functiuon of RNA is protien
synthesis by the process of translation
In eukaryotes, noncoding RNA comes in several
varieties,
most prominently transfer RNA (tRNA) and
ribosomal RNA (rRNA). As previously mentioned,
both tRNA and rRNA have long been known to be
essential in the translation of mRNA to proteins.
