This document discusses the genetic material in microbes. It begins by covering how Gierer and Schramm discovered that tobacco mosaic virus (TMV) contains RNA as its genetic material after isolating RNA from TMV and showing it was sufficient to infect tobacco plants. It then discusses the properties DNA must have to serve as a genetic material, including being present in all cells, able to store and transmit information stably, replicate accurately, and direct cell functions. The document concludes by covering the chemical stability of DNA, which depends on hydrogen bonding between bases and interactions between the hydrophobic bases that stack inside the helix.

1. SEMESTER- V - PAPER – XII- MICROBIAL GENETICS
UNIT- 1- THE GENETIC MATRIAL
1. Discovery of RNA as a viral Genetic Material
i. Gierer and Schramm Experiment ( TMV )
2. Properties of DNA as a Genetic Material
3. Chemical Stability of DNA and its Information Content
By
Asst. Prof. Santosh Napte
Dept. Of Microbiology ,
Sambhajirao Kendre Mahavidhyalaya, Jalkot, Dist. -
Latur

2. 1. Discovery of RNA as a viral Genetic Material
Gierer and Schramm Experiment ( TMV )
All living organisms have DNA as a genetic material except some
viruses.
In such viruses the genetic material is RNA---- ss RNA or dsRNA is
present enveloped by protein coat.

3. Human Diseases caused by RNA Viruses
Sr. No. Name of Disease Causative agent ( Name of
RNA Virus )
Ss RNA or ds RNA
1. SARS ( Severe Acute Respiratory
Syndrome )
SARS-CoV Ss RNA
2. Influenza ( Flu ) Influenza Virus Ss RNA
3. Hepatitis Hepatitis A, B, C, D and
E Virus
Ss RNA
4. Measels Measels morbillivirus Ss RNA
5. AIDS HIV Ss RNA
6. COVID- 19 Novel Corona Virus ( nCoV
)
Ss RNA

4. Plant Diseases caused by RNA Viruses
Sr. No. Name of Disease Causative agent ( Name of
RNA Virus )
Ss RNA or ds RNA
1. Tobacco Mosaic Virus ( TMV ) Mosaic diseas in tobacco Ss RNA
2. Tomato Spotted Wilt Virus (TSWV
)
Spots and Wilting Ss RNA
3. Cucumber Mosaic Virus ( CMV ) Cucumber Mosaic Ss RNA
4. Potato Virus Y ( PVY ) Leaf drop , necrotic
lessions
Ss RNA

5. Gierer and Schramm Experiment ( TMV )
• Alfred Gierer and
Gerhard Schramm ----
RNA isolated from TMV is
sufficient to infect
tobacco plants and the
production of new TMV
particles.
• This confirms that RNA
carries genetic
information in viruses

6. Gierer and Schramm Experiment ( TMV )

8. 2. Properties of DNA as a Genetic Material
Any substance must fulfill following properties
and functions to qualify as a genetic material.......
1. Must be present in all cells.
2. Must contain all biologically useful information in a stable
form.
3. Must be able to store information in a coded form to control
and express all biological functions.
4. Should be able to replicate properly and form true copies of
next generation.
5. Should be able to generate its own type and also new
different types of molecules.

9. 6. should also be capable of variations through
recombination and mutations and resulting variations
must be stable and inheritable.
7. Should be capable of express in a different way so
that different parts of an organism can take a specific
forms and functions though the genetic material is
same.

10. 2. Properties of DNA as a Genetic Material
Any substance which form the heritable material must fulfill some essential requirements and
DNA was found to fulfill all requirements that’s why DNA acts as a genetic material.
These essential requirements includes..
Ability to store genetic
information and to transmit it to
the cell as per requirement.
Ability to transfer its
information to daughter cells
minimal error.
Physical and chemical stability
in order that information is not
lost.
Capability for genetic change,
though without major loss of
parental information.

11. 2. Properties of DNA as a Genetic Material........Continues...
Present in all cells of organisms. Each
somatic cell of given organism have
double amount of DNA as compared to
their gametic cells.
Shows wide variety due to unlimited
variety of sequences.
Replicates properly during interphase of
cell division and daughter DNAs have
same genetic information as like parent
DNA.
Sometimes causes mutations in the
genes.
Stores genetic information in the form of
triplet code and expresses this by
transcription and translation to produce
proteins which in turn controls all
metabolic activities and structure of cells.

12. 2. Properties of DNA as a Genetic Material........Continues...
Responsible for the process
of differentiation it
means different genes
remain functional in different
cells so that acquire specific
structure and functions.
If damaged , can repair itself
so that the genetic
information get preserved.

13. SEMESTER- V - PAPER – XII- MICROBIAL
GENETICS
UNIT- 1- THE GENETIC MATRIAL
Chemical Stability of DNA and its Information Content
By
Asst. Prof. Santosh Napte
Dept. Of Microbiology ,
Sambhajirao Kendre Mahavidhyalaya, Jalkot, Dist. - Latur

14. Chemical Stability of DNA and its Information Content
 Stability of DNA double helix depends on
Hydrogen bonds between bases,
Hydrogen bonds between bases and surrounding water molecules,
Base-stacking interactions between adjacent bases.
 Slight variations in the DNA sequence can affect the stability of the DNA
duplex. For example, mutations due to errors occur during DNA
replication can result in mismatches that forms unstable duplexes.
But proofreading enzymes recognizes this mutation and replace it with
the correct nucleotide .
 To gain an insight into DNA duplex stability scientists have studied the
structure and thermodynamic stability of a variety of DNA duplexes by
using a combination of physical methods including X-ray
crystallography, ultraviolet (UV) melting and NMR.

15. Factors Affecting Stability of DNA Double Helix
 In long lived organisms a single DNA molecule may have to
last one hundred years or more.
 The information contained in the molecule is passed on to
successive generations for millions of years with only small
changes.
 Thus DNA molecule must have great stability.
DNA duplex stability is determined primarily by hydrogen
bonding, but base stacking also plays an important role.
1. Hydrogen bonding.
2. Hydrophobic Interactions
3. Ionic Interactions / Force
4. Base Stacking Interactions.

17. Factors Affecting Stability of DNA Double Helix
1. Hydrogen bonding

19. 2. DNA stability—Hydrophobic Interactions
 Present between the planer base pairs sabilizes bases on the inside of the helix, so
provide stability to the structure but do not contribute to the specificity.
 Hydrophobic interactions are important for the folding, stability and biological
activity.

20. Factors Affecting Stability of DNA Double Helix
3 . Ionic Interactions
Ion- ion repulsion of the negatively charged
phosphate makes DNA duplex unstable.
But the presence of Mg 2+ and cationic proteins
with abundant arginine and lysine residues
stabilizes the double helix.
Double stranded helix structure thus promoted
by having phosphates on outside interact with
water and counter ions such as K+ and Mg++.