3. Understanding Genetics
We resemble and differ because of
Genetic configurations
Parents - Son - Daughter, how they
resemble each other.
They breed true from Generation to
Generation
But vary in small proportions in
progeny.
Bacteria too obey the laws of Genetics
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4. Beginning of Bacterial
Genetics
4
• The principles of Genetics were applied to
bacteria and viruses
• Advances in Genetic process also of lead
to fundamental advances in Biology and
Biochemistry.
A Birth of New Branch of Science
Molecular Biology
5. 5
DNA
( Deoxyribonucleic Acid )
• DNA is composed of Many Units of
Adenine – Thymine A – T
Guanine – Cytosine G - C
A+ T
G+C proportion differ for each species
DNA replicates first unwinding at one end to form a
fork
Each strand of fork acting as template for the
synthesis of complementary strand
6. DNA
• A DNA molecule is
composed of two
chains of Nucleotides
wound together in the
form of a Double
Helix
• Each chain has back
bone of Deoxyribose
and Phosphates
residues arranged
alternatively 6
7. Structure of DNA
• Attached to each
Deoxyribose and
phosphate residues
arranged alternatively
• Attached to each
Deoxyribose are of four
nitrogen bases
• Purines - Adenine,
Guanine
• Pyramidine
Thymidine and Cytosine
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8. 8
How RNA differs from DNA
• RNA contains - Sugar Ribose instead
of Deoxyribose
• Uracil is present instead of Thymine
9. 9
Knowledge on DNA lead to
advances in Molecular Biology
• Central dogma of Life – Deoxyribonucleic acid
• DNA carries the Genetic information
• DNA is transcribed to RNA –Proteins-Enzymes
DNA is a store house of Protein synthesis DNA acts
a Template for synthesis of mRNA
Virus differs from other as they contains either
DNA or RNA
10. What is a Gene
• Gene is a sequence
of DNA carrying
codons specifying for
particular polypeptide.
• DNA contains many
Genes ( A
combinations of
hundreds and
thousands of
Nucleotides )
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11. Bacterial Chromosome
• Contains a Double stranded molecules of
DNA arranged in circular form.
• Length 1,ooo microns.
• Bacterial DNA contains about
4,000kilobases
• I kb = 1000 base pairs ( A-T ) ( G-C)
• Humans have about 3,000 kb pairs.
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12. 20
Extra chromosomal
Genetic Elements
Bacteria posses Extra chromosomal
genetic elements
Not Essential for survival of Bacteria
But makes the Bacteria Resistant to
antibiotics, and makes them survive
Able to produce toxins
13. Plasmids
• Plasmids are circular
DNA molecules present
in the cytoplasm of the
Bacteria
• Capable of Autonomous
replication
• Can transfer genes from
one cell to other
• Act as vectors in Genetic
engineering.
• Can also present in
Yeasts
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15. 15
Plasmids
• Plasmid seem to be ubiquitous in bacteria, May
encode genetic information for properties
1 Resistance to Antibiotics
2 Bacteriocins production
3 Enterotoxin production
4 Enhanced pathogen city
5 Reduced Sensitivity to
mutagens
6 Degrade complex organic molecules
16. Plasmids
• Can be integrated
with Chromosomal
DNA
• Episomes -
Integrated form of
plasmid with DNA
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17. Potentials of Plasmids
• Plasmids can be self
transmissible and
Non transmissible
• Transfers the Sex and
Drug resistance with
the help of restriction
endonucleases
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19. Mutations in Bacteria
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• Bacteria Multiply by asexual binary fission
• Altered Nucleotide sequence expresses new or
altered characteristics
• Selective value to the organism
• Evolutionary value
• Acquires Antibiotic resistance grows in body
without inhibition
• Become a prominent organism
• Phenotypic variation occurs when genes
changes in response to the environment but
reversible.
20. The three bacterial sexual
processes
– 1. Conjugation: direct transfer of
DNA from one bacterial cell to
another.
–2. Transduction: use of a
Bacteriophages (bacterial virus) to
transfer DNA between cells.
–3. Transformation: naked DNA is
taken up from the environment by
bacterial cells
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21. What is Transformation
• Transformation is defined as transfer of Genetic
information through the activity of DNA
• Griffith experiment
Mice injected with Live non capsulated ( R )
Pneumococci
with heat killed capsulated (S) Pneumococci
Lead to death of Mice with isolation of Live
capsulated Pneumococci
It means that some factor from Dead
pneumococci transferred to live non pathogenic
Pneumococci
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25. DNA transfer through
Bacteriophages
• When the Phage
particle infects
another bacteria
DNA transfer is
effected and the
recipient cell
acquires new
characters coded
by donor DNA
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26. Conjugation
• A process by which a Donor cell or male cell
makes contact with another cell, the recipient or
Female cell.
• DNA is directly transferable
• Plasmid Carry genetic information necessary for
conjugation to occur.
• Only cell that contain such plasmids can act as
donor. the cell lacking a corresponding plasmid
act as recipient.
• Requires direct contact between donor and
recipient
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27. Conjugation
• The ability to conjugate is
conferred by the F plasmid. A
plasmid is a small circle of DNA
that replicates independently of
the chromosome. Bacterial cells
that contain an F plasmid are
called “F+”. Bacteria that don’t
have an F plasmids called “F-”
57
28. Conjugation - Transferring
genes with plasmids
• Plasmids mediating
conjugation carry
genes coding for
properties, of 1-2
microns long
protein appendage
termed Pilus on the
Donor cell
28
