Genetic material Anant Mohan Sharma All cell have the capability to give rise to the cell and the encoded information in living cell is passed from one generation to another. The information encoded material is the genetic material or hereditary material of the cell.  The genetic material is long sequence of nucleic acids that contain the genetic instruction. Nucleic acid are macromolecules in the form of DNA or RNA. Experimental evidences Griffith’s experiment Avery, MacLeod &McCarty experiment Hershey & Chase experiment RNA as genetic material DNA structure Z- DNA V. Sasisekharan RL model Types of RNA

1. Genetic
material
Anant Mohan Sharma
M.Sc. biotech 1st sem

2. Introduction
1
Experimental
Evidences
2
Structure of
DNA
3
Type of RNA
4
DNA Vs.
RNA
5

3. LET’s BEGIN NOW

4. Introduction
 All cell have the capability to give rise to the cell and
the encoded information in living cell is passed from
one generation to another. The information encoded
material is the genetic material or hereditary material
of the cell.
 The genetic material is long sequence of nucleic
acids that contain the genetic instruction. Nucleic
acid are macromolecules in the form of DNA or
RNA.

5. Experimental
evidences

6. Griffith’s experiment
 In 1928, Frederick Griffith performed an experiment using pneumonia bacteria and mice.
 He used two strains of Streptococcus pneumoniae.
 (1) Smooth; The cells of strains forming smooth (S) colonies have a smooth glittering
appearance due to presence of strain-specific polysaccharides (a polymer of glucose
and glucuronic acid) capsule. Such strains are able to produce pneumonia and are
called virulent.
 (2) Rough ; The cells of stain lack this capsule and they produce dull rough (R) colonies.
Such stains are termed as avirulent since they cannot produce pneumonia.
He performed a series of experiment on mice with different strain of Streptococcus
pneumoniae as follow-

8. Griffith’s conclusion
 Griffith concluded that the live R strain bacteria must
have absorbed genetic material from the dead S strain
bacteria, and since heat denatures protein, the protein
in the bacterial chromosomes was not the genetic
material. This evidence pointed to DNA as being the
genetic material.

9. Avery, MacLeod &McCarty experiment
 In 1944, Oswald Avery, Colin
MacLeod, and Maclyn McCarty
revisited Griffith's experiment and
concluded the transforming factor was
DNA.
 They treated highly purified extract
from Type IIIS cells with Dnase,
protease, Rnase, lipase and tested for
its ability to transform Type II R cells
to Type IIIS.
 Only Deoxyribonuclease had any
effect on the transforming activity of
the DNA preparation.

10. Hershey & Chase
experiment
 In 1952, Alfred Hershey and Martha Chase did an
experiment to proof that genetic information is
carried by DNA.
 They uses bacteriophage because people knew
that viruses were composed of DNA (or RNA) inside
a protein coat/shell called a capsid. And viruses
replicate by taking over the host cell metabolic
functions to make more virus.
 They radiolabeled phage DNA with radio-isotope
32P where as protein coat was labelled with 35S.

12. A sample of an E.coli culture was infected with labelled T2 phage. After a short
incubation period, the suspension was spun for a few minutes in warring Blender at
10,000 rpm. This treatment served the connections between the viruses and bacteria.
The resulting suspension was centrifuged The pellet contained infected bacteria,
where as supernatant contained smaller particles. These fractions were analyzed for
32P and 35S to determine the location of the phage DNA and the protein coat.
The results of the experiment were:
 1. Most of the phage DNA was found in the bacteria.
 2. Most of the phage protein was found in the supernatant.
 3. The blender treatment did not prevent the infection.
 4. The progeny of T2 phage contained the parental 32P and not the parental 35S.

13. RNA as genetic material
Some viruses contain an RNA core rather than a DNA core.
 In 1956, it was demonstrated that when purified RNA from tobacco mosaic virus (TMV) is spread
on tobacco leaves, the characteristic lesions caused by this virus subsequently appear on the
leaves. Thus, it was concluded that RNA is the genetic material of this virus.
 Soon afterward, another type of experiment with TMV was reported by Heinz Fraenkel-Conrat
and B. Singer.
 These scientists discovered that the RNA core and the protein coat from wild-type TMV and other
viral strains could be isolated separately. In their work, RNA and coat proteins were separated
and isolated from TMV and a second viral strain, Holmes ribgrass (HR).
 Then, mixed viruses were reconstituted from the RNA of one strain and the protein of the other.
When this “hybrid” virus was spread on tobacco leaves, the lesions that developed corresponded
to the type of RNA in the reconstituted virus—that is, viruses with wild-type TMV RNA and HR
protein coats produced TMV lesions, and vice versa. Again, it was concluded that RNA serves as
the genetic material in these viruses.

15. DNA structure
 DNA is a long thread like unbranched polymeric
molecule of heredity. DNA molecule composed of
repeating sub units called nucleotides. Each
nucleotide composed of (i) a phosphate group (ii) a
five carbon deoxyribose sugar (iii) cyclic nitrogen
containing compound called nitrogenous base.
 The correct structure of DNA was proposed by
J.D.Watson and F.H.C Crick (1953). The double
helix model proposed by them is based on two
evidence.
 On the basis of Chargaff’s chemical data and
crystallographic data by Wilkins and Franklins,
Watson and Crick proposed the structure of DNA.
The important features of their model are-

16. 1. DNA exists in double helix in which two polynucleotide chain coiled about one
another in a spiral way.
2. Each polynucleotide chain consists of sequence of nucleotides linked together by
phosphodiester bonds and two polynucleotide chains held together by hydrogen
bonding between bases.
3. The base pairs are stacked between two chains perpendicular to the axis of the
molecule similar to the steps of a spiral staircase. The base pairs in DNA stacked
3.4 A° apart with 10 base pairs per turn (360°) of the double helix.
4. The base pairing in DNA molecule is specific i.e. Adenine pairs with Thymine (A=T)
and Cytosine pair with Guanine (C=G). So each base pair consists one purine and
one pyrimidine.
5. The two strands of the DNA are complementary in nature (non-identical) i.e. once
the sequences of bases is one strand is known, the sequences of bases in the other
strand is also known because of specific base pairing. The complementary nature is
very important for storing and transmitting the genetic information.

17. 6. The purine and pyrimidine bases are on the inside of the helix where as the
phosphate and deoxyribose unit are on the outside. The sugar phosphate
backbones of the two complementary strands are antiparallel. Among two
strand of DNA, one strand go from 3’ carbon of one nucleotide to 5’ carbon of
the adjacent nucleotide. Whereas the complementary strand go from 5’ to 3’
carbon. This mechanism is very important in considering the mechanism of
replication of DNA.
7. The high degree of stability of DNA is due to more number of hydrogen bonds.

18. Pentose sugar
Ribose sugar
Deoxyribose sugar

19. Nitrogenous base

20. Z- DNA
 Z-DNA mostly found in alternating purine- pyrimidine sequence (CG and TG)
 Z-DNA is thinner (18 A ) than B-DNA.
 The bases are shifted to the periphery of the helix and there is only one deep, narrow
groove equivalent to the minor groove in B-DNA.
 In B-DNA , where a repeating unit is 1b.p , but in Z-DNA the repeating unit is 2b.p.
 The backbone follows a zigzag pathway as opposed to smooth path in B-DNA.
 The sugar and glycosidic bond conformation alternate.
 C2’ end in anti and C3’ in syn configuration.
 Electrostatic interaction play a crucial role in Z-DNA formation. Therefore Z-DNA is
stabilized by high salt concentration or polyvalent cation, that shield interphosphate
repulsion better than monovalent.

21. V. Sasisekharan RL model
 During 1976-80, V. Sasisekharan and his coworkers, of Indian Institute of Science,
Bangalore, emphasized that the right handed form (R) of double helical B-DNA can
not easily explain the unwinding of the duplex due to topological difficulties. They
suggested that right handed (R) and le handed (L) double helices are equally likely
and therefore proposed a new RL model. In this model a B-DNA structure with
alternating right handed and left handed segments of approximately five base pairs, in
a repeat of ten base pairs, was proposed.is model provides for conformation flexibility.
There is strong experimental evidence available in favour of RL model, although one
does not know the possible maximum continuous lengths of right handed and left
handed segment of DNA.
 The combination of B-DNA with Z-DNA is an example of RL Model. In such structure,
bends are formed at place where right and left segment are joined. The bend region
satisfy the allowed stereochemistry and retain the base pairing scheme of watson and
crick, however an unusual kind of stacking arrangement result in the bend region
called inverted stacking.

22. DNA Supercoiling
 “Supercoiling” means the coiling of a
coil.
 DNA is coiled in the form of a double
helix, with both strands of the DNA
coiling around an axis. The further
coiling of that axis upon itself produces
DNA supercoiling.
 When there is no net bending of the
DNA axis upon itself, the DNA is said to
be in a relaxed state.
 Supercoiling can arise in any helical
structure in which the 2 end are
constrained in some way.

23. Type of DNA

24. Types of RNA
 RNA or ribonucleic acid is a polymer of
nucleotides which is made up of a ribose
sugar, a phosphate, and bases such as
adenine, guanine, cytosine, and uracil. It is a
polymeric molecule essential in various
biological roles in coding, decoding, regulation,
and expression of genes.

25. Types of RNA
Messenger RNA (mRNA)
mRNA transcribes the genetic
code from DNA into a form that
can be read and used to make
proteins. mRNA carries genetic
information from the nucleus to
the cytoplasm of a cell.
Ribosomal RNA (rRNA)
rRNA directs the translation of
mRNA into proteins
Transfer RNA (tRNA)
Transfer RNA brings or transfers
amino acids to the ribosome that
correspond to each three-
nucleotide codon of rRNA. The
amino acids then can be joined
together and processed to make
polypeptides and proteins.
MicroRNAs
MicroRNAs are small ncRNAs
of ~22 nucleotides (nt). These
RNA species mediate post-
transcriptional gene silencing
through RNA interference
(RNAi)

26. SnoRNA
SnoRNA is involved in making
ribosomes and telomeres
siRNA
small, bind to complementary
RNA sequences targeting them
for destruction
SnRNA
Small nuclear RNA involved
with the processing of larger
precursor RNA molecules
XIST RNA
inactivates one of the two X
chromosomes in females

27. DNA Vs. RNA
Parameter DNA RNA
1. Name Deoxyribonucleic acid Ribonucleic acid
2. Function Store genetic information
and hereditary
Convert genetic information
into protein
3. Structure Double strand ; helix Single stranded helical
4. Molecular wt. 2 to 6 million 25k to 2 million
5. Length L0onger than rna Variable in length(in range
kb)
6. Sugar Deoxyribose sugar Ribose sugar
7. Nitrogenous base A-T::G-C A-U::G-C
8. Geometry Mainly in B form Helix geomety in A form
9. Stability Highly stable Less stable
10. purine: pyrimidine Always 1:1 highly variable

28. Parameter DNA RNA
11. Chargaff’s rule Follow Do not follow
12. Histone interaction Associated with histone Not associated
13. Location In nucleus, mitochondria
and chloroplast
Found in nucleus,
mitochondria, chloroplast
and cytoplasm
14. Grooves Comparatively small Large grooves
15. Catalytical activity No enzyme activity Some rna act as enzyme
16. UV radiation Extremely sensitive Less sensitive
17. Sugar pucker C2’ endo C3’ endo form
18. Alkaline condition Stable Unstable

29. Thank you