2. 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
5. Prokaryotes Vs Eukaryotes
Genetics
Prokaryotes Eukaryotes
Prokaryotes are haploid eukaryotes are often diploid
contain a single circular
chromosome.
eukaryotes have linear chromosomes,
usually more than 1
Prokaryotes often contain
“plasmids”.
Doesnot contain plasmids
In prokaryotes, translation is
coupled to transcription:
translation of the new RNA
molecule starts before
transcription is finished
In eukaryotes, transcription of genes
in RNA occurs in the nucleus, and
translation of that RNA into protein
occurs in the cytoplasm. The two
processes are separated from each
other.
6. 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
7. 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
8. Structure of DNA
Attached to each
Deoxyribose and
phosphate residues
arranged alternatively
Attached to each
Deoxyribose are of four
nitrogen bases
Purines - Adenine,
Guanine
Pyrimidines
Thymidine and Cytosine
9. How RNA differs from DNA
RNA contains - Sugar Ribose instead of
Deoxyribose
Uracil is present instead of Thymine
Types of RNA
Messenger RNA mRNA
Ribosomal RNA rRNA
Transfer RNA tRNA
10. What is a Code in
Genetics?
Code is a unit consists of sequence of three
Bases
Code is triplet A-T- C
A code can make single Amino acid
More than one code present for making
similar sequence of Amino acid
AGA make Arginine
AGC, CGU, CGG, also code for similar Amino
acid
Some Codons UAA don't code for any Amino
acid called as Nonsense codon
11. What is a Gene?
Gene is a sequence of
DNA carrying codons
specifying for particular
polypeptide.
DNA contains many
Genes(combinations of
hundreds and
thousands of
Nucleotides )
12. Bacterial Chromosome
Contains a Double stranded molecules
of DNA arranged in circular form.
Length 1,000 microns.
Bacterial DNA contains about
4,000kilobases
1 kb = 1000 base pairs (A-T) (G-C)
13. 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
& also able to produce toxins
14. Plasmids
Plasmids are circular
DNA molecules present
in the cytoplasm of the
Bacteria
Their size varies from 1
kbp to over 400
kilobase pairs (kbp).
Capable of Autonomous
replication
Can transfer genes from
one cell to other
Act as vectors in Genetic
engineering.
15. Plasmids
Plasmid seem to be ubiquitous in bacteria, May encode
genetic information for properties
1 Resitance to Antibiotics
2 Bacteriocins production
3 Enterotoxin production
4 Enhanced pathogenicity
5 Reduced Sensitivity to mutagens
6 Degrade complex organic molecules
16. Plasmids are classified
1. by their ability to be transferred to
other bacteria
Conjugative
The sexual transfer of plasmids to another
bacterium through a pilus.
Non-conjugative
Non-conjugative plasmids don’t initiate conjugaison.
They can only be transferred with the help of
conjugative plasmids.
17. Mobilisable
An intermediate class of plasmids are mobilisable, and
carry only a subset of the genes
These plasmids can 'parasitise' another plasmid,
transferring at high frequency
presence of a conjugative plasmid
Incompatibility groups:
Several types of plasmids could coexist in a single cell.
On the other hand, related plasmids are often
'incompatible', resulting in the loss of one of them from the
cell line.
18. 2. Function
1. Fertility-(F) plasmids,
They are capable of conjugation (they contains the genes for
the pili).
2. Resistance-(R) plasmids,
Contain gene (s) that can build resistance against one or
several antibiotics or poisons.
3. Col-plasmids,
Contain genes coding for colicines, proteins that can kill other
bacteria. .
19. 4. Degradative plasmids,
able to digest unusual substances, e.g., toluene or
salicylic acid
5. Virulence plasmids
turn a bacterium into a pathogen.
6. Addiction system.
These plasmids produce both a long-lived poison and a
short-lived antidote.
Daughter cells that retain a copy of the plasmid survive
while a daughter cell that fails to inherit the plasmid dies
or suffers a reduced growth-rate because of the lingering
poison from the parent cell.
20. Plasmids
Can be integrated
with Chromosomal
DNA
Episomes
-Integrated form of
plasmid with DNA
21. Potentials of Plasmids
Plasmids can be self
transmissible and
Non transmissible
Transfers the Sex
and Drug resistance
with the help of
restriction end
nucleases
22. Genotypic & Phenotypic variation
Genome – Sum total of Gene that make
up the genetic apparatus of cell
established as Genotype.
Hereditary constitution of cell this
transmitted to its progeny
Phenotype – is the physical expression
of genotype in a environment & can
change according to environment.
23. Phenotypic variation
Exhibit – different phenotypes
Appearance differs in different situations.
Eg: Typhoid bacilli flagellated normally
But grown in Phenol agar don't grow flagella so
flagella are lost physical variation
Lactose fermentation in E.coli dependent on Beta
Galactosidase
When lactose present - test is positive
When lactose is absent - test turns negative
24. Genotypic variations
Stable, heritable and not influenced by
environment
May occur by
Mutations
Genotypic by transfer of genes
Transformation
Transduction(Lysogenic conversion)
Conjugation
25. Mutations
Mutation is a Random, Undirected,
Heritable variation
Caused by alteration in the Nucleotide
sequence at some point of DNA which can
occur due to
Addition
Deletion
Substitution
of one or more bases
26.
27. Mutation Rate
Different types of mutations can occur at
different frequencies. For a typical
bacterium, mutation rates of 10–7
to 10–11
per base pair are generally seen
Although RNA and DNA polymerases
make errors at about the same rate, RNA
genomes typically accumulate
mutations at much higher frequencies
than DNA genomes.
29. Multiple Mutations
Causes extensive chromosomal rearrangement
Missense mutation
Triplet code is altered so as to specify an
aminoacid different from that normally located at
particular position in the protein.
Nonsense mutation
Deletion of nucleotide within a gene may
cause premature polypeptide chain termination
by nonsense codon
Transversion is Substitution of purine for
pyramidine or vice versa in the base pairing
31. Replica Plating Method
A common way to find bacterial mutants is
replica plating, which means making two
identical copies of the colonies on a petri plate
under different conditions.
For instance, if you were looking for trp-
auxotrophs, one plate would contain added
tryptophan and the other plate would not have
any tryptophan in it.
Bacteria are first spread on the permissive
plate, the plate that allows both mutants and wild
type to grow, the plate containing tryptophan in
this case..
32. They are allowed to grow for a while, then a
copy of the plate is made by pressing a
piece of velvet onto the surface of the
plate
then moving it to a fresh plate with the
restrictive condition (no tryptophan).
The velvet transfers some cells from each
colony to an identical position on the
restrictive plate.
33. Colonies that grow on the permissive plate
but not the restrictive plate are (probably)
trp- auxotrophs, because they can only grow
if tryptophan is supplied
35. Transmission of Genetic material
( Gene Transfer )
Different Mechanisms
Transformation
Transduction
Conjugation
36. Transformation
Transformation is defined as transfer of Genetic
information through the activity of free DNA
first experiment that showed DNA was the
genetic information
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
38. Certain prokaryotes exhibit competence, a state
in which cells are able to take up free DNA
released by other bacteria.
Incorporation of donor DNA into a recipient cell
requires the activity of single-stranded binding
protein, RecA protein, and several other
enzymes.
Only competent cells are transformable
39.
40. 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
41. 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
44. Pilus helps Conjugation
Different types of Pilus
are specified by different
types of plasmids and
can help in aid of
plasmid classification.
Only one strand of
circular DNA of the
plasmid nicked upon at
a specific site and
passed into a recipient.
Spread to all other cells.
45. F factor
Transfer factor that
contains the genetic
information necessary
for synthesis of Sex
Pilus and for self
transfer without any
other identifiable
genetic materials such
as drug resistance
46. F+
called as Donor bacteria can transform F-
into F+
cell
Can be Episomes able to exist in some cells in the
integrated state in the donor cell chromosome
Can transform chromosomal genes to recruitment
with high frequency are known as Hfr cells
Conversion of F+
cells into Hfr state is reversible.
F factor incorporates some chromosomal genes
and is called as F’
Sexduction : process of transfer of host genes
through F’ factor
48. 48
Historical
Lederberg & Zinder
Transduction was first discovered in 1952 by
Joshua Lederberg and Norton Zinder
Joshua Lederberg Norton
Zinder
49. How transduction was discovered
49
Studied in Salmonella typhimurium
Plated two auxotrophic strains (LA-2 and LA-22)
individually on minimal medium, no cells grew.
Plated a mixture of the two auxotrophic strains on
minimal medium, cells grew into colonies.
Thus, genetic exchange was taking place between
the two cell types.
www.bio.ilstu.edu
52. GENERALIZED TRANSDUCTION
process by which any bacterial gene may be
transferred to another bacterium via a
bacteriophage.
typically carries only bacterial DNA and no
viral DNA
53. Generalised Transduction
53
1. A lytic bacteriophage adsorbs
to a susceptible bacterium.
2. The bacteriophage genome
enters the bacterium. The
genome directs the bacterium's
metabolic machinery to
manufacture bacteriophage
components and enzymes
www.2dix.com
54. 54
3. Occasionally, a
bacteriophage head or capsid
assembles around a fragment of
donor bacterium's nucleoid
instead of a phage genome by
mistake.
steps in Generalised Transduction (cont’d)
4. The bacteriophages are released.
www.2dix.com
55. steps in Generalised Transduction (cont’d)
55
5. The bacteriophage
carrying the donor
bacterium's DNA adsorbs
to a recipient bacterium
6. The bacteriophage inserts the
donor bacterium's DNA it is
carrying into the recipient
bacterium .
www.2dix.com
56. 56
steps in Generalised Transduction (contd)
7. The donor bacterium's DNA is exchanged for some
of the recipient's DNA.
www.2dix.com
57. SPECIALIZED TRANSDUCTION
Discovered by Morse et al
Process by which a restricted set of bacterial
genes are transferred to another bacterium
Partially coded prophage DNA is called a
"heterogenote".
58. Specialised Transduction
58
1. A temperate bacteriophage
adsorbs to a susceptible
bacterium and injects its
genome .
2. The bacteriophage inserts its
genome into the bacterium's
nucleoid to become a prophage.
www.2dix.com
59. steps in Specialised Transduction (cont’d)
59
3. Occasionally during
spontaneous induction, a small
piece of the donor bacterium's
DNA is picked up as part of the
phage's genome in place of
some of the phage DNA which
remains in the bacterium's
nucleoid.
4. As the bacteriophage
replicates, the segment of
bacterial DNA replicates as part
of the phage's genome. Every
phage now carries that segment
of bacterial DNA.www.2dix.com
60. steps in Specialised Transduction (cont’d)
60
5. The bacteriophage adsorbs to
a recipient bacterium and injects
its genome.
6. The bacteriophage genome
carrying the donor bacterial
DNA inserts into the recipient
bacterium's nucleoid.
www.2dix.com
61. Genetic Mechanisms of Drug
Resistance
Bacteria acquire drug resistance through several
Mechanisms
Mutations
Genetic transfer
Transformation,
Transduction
Conjugation
Several Biochemical Mechanisms
Decreasing permeability of drugs,
Attaining alternative pathways
Produce enzymes and inactivate drugs
63. Transposons and Insertion
Sequences
Transposons and insertion sequences are
genetic elements that can move from one
location on a chromosome to another by a
process called transposition.
a type of site-specific recombination.
64.
65.
66. Transposition is linked to the presence of
special genetic elements called transposable
elements. Transposition can be either
replicative or conservative
67.
68.
69. Summary
A DNA molecule is composed of two chains of
Nucleotides wound together in the form of a Double
Helix
Gene is a sequence of DNA carrying codons specifying
for particular polypeptide
Plasmids are circular DNA molecules present in the
cytoplasm of the Bacteria
Phenotype variation – is the physical expression of
genotype in a environment & can change according to
environment
Genotype variation – Stable, heritable and not
influenced by environment
70. Mutation – alteration in the Nucleotide sequence at some
point of DNA which can occur due to Addition, Deletion,
Substitution of one or more bases
Replica plating
Transformation – is defined as transfer of Genetic
information through the activity of free DNA
Conjugation – process by which a Donor cell or
male cell makes contact with another cell, the
recipient or Female cell.
71. Transduction – is defined as transfer of portion of DNA
from one bacteria to another by Bacteriophages
Generalised transduction – process by which any
bacterial gene may be transferred to another bacterium
via a bacteriophage
Specialised transduction – Process by which a
restricted set of bacterial genes are transferred to another
bacterium
