Bacterial genetics

Bacterial Genetics describes about Transformation, Transduction, Conjugation processes in details and about the mutation occur in microbes.

1. Bacterial Genetics Bacterial Genetics
By – Mr. Gunjal Prasad N.By – Mr. Gunjal Prasad N.
M.Sc. Medical Microbiology, PGDCRA. M.Sc. Medical Microbiology, PGDCRA.
P.D.V.V.P.F’s Medical College,P.D.V.V.P.F’s Medical College,
Ahmednagar.Ahmednagar.

2. INTRODUCTIOINTRODUCTIO

GENETICSGENETICS (Definition) – The study of Heredity & Variation (Definition) – The study of Heredity & Variation
between generation is known as between generation is known as Genetics.Genetics.
Deals with mechanism of transmission of hereditary Deals with mechanism of transmission of hereditary
materials (Genes).materials (Genes).

All characteristics are maintained in the DNA.All characteristics are maintained in the DNA.

Chromosomal DNA plays major role in maintenance of this Chromosomal DNA plays major role in maintenance of this
characters constant from one generation to another.characters constant from one generation to another.
This is maintained by the most accurate replication of its This is maintained by the most accurate replication of its
DNA.DNA.

3. BASIC PRINCIPALSBASIC PRINCIPALS
DNA molecule is made up of two DNA molecule is made up of two
complementary nucleotides.complementary nucleotides.

Which are twisted together to form Which are twisted together to form
Double helix as proposed by Double helix as proposed by Watson Watson
and Crick.and Crick.

NUCLEOTIDES –NUCLEOTIDES – Each Nucleotide is Each Nucleotide is
composed of composed of

A. Pentose sugar A. Pentose sugar (Deoxyribose).(Deoxyribose).
B. B. Phosphate Group.Phosphate Group.

C. One of four C. One of four nitrogenous bases nitrogenous bases
attached to pentose sugar. attached to pentose sugar.

4. A. DEOXYRIBOSE SUGAR – A. DEOXYRIBOSE SUGAR –
It is a 5 carbon compound = CIt is a 5 carbon compound = C
55HH
1010OO
4 4 ( A Pentose ).( A Pentose ).
Known as Known as DeoxyriboseDeoxyribose = One Carbon less than Ribose sugar = One Carbon less than Ribose sugar
(De = Less).(De = Less).
B. PHOSPHATE GROUP –B. PHOSPHATE GROUP –
Consist phosphoric group (HConsist phosphoric group (H
33POPO
44).).
It is attached to one pentose sugar at 5Carbon & to adjacent It is attached to one pentose sugar at 5Carbon & to adjacent
pentose sugar at 3Carbon to form a chain.pentose sugar at 3Carbon to form a chain.
C. NITROGEN BASES – C. NITROGEN BASES –
Nitrogen containing base substances.Nitrogen containing base substances.
Two types – Two types – A. Purines B. Pyrimidines. A. Purines B. Pyrimidines.
Length of bacterial Nucleus containing circular chromosome Length of bacterial Nucleus containing circular chromosome
approx. 1000 approx. 1000 µm long when straightened.µm long when straightened.
Contains near about 3000 – 4000 different genes. Contains near about 3000 – 4000 different genes.

5. DNA structureDNA structure
Double helix Double helix
Sugar-phosphate Sugar-phosphate
backbonebackbone
Bases on inside, H Bases on inside, H
bondedbonded
Strands anti-parallel Strands anti-parallel

6. Each strand of DNA has a backbone of deoxyribose sugar & Each strand of DNA has a backbone of deoxyribose sugar &
phosphate group.phosphate group.
Four nitrogen bases – Four nitrogen bases – Two of Purines Two of Purines i) Adenine (A), ii) Guanine i) Adenine (A), ii) Guanine
(G), (G), Two of Pyrimidines Two of Pyrimidines i) Thymine (T), ii) Cytosine (C).i) Thymine (T), ii) Cytosine (C).
One of these 4 nitrogenous bases attached to each deoxyribose One of these 4 nitrogenous bases attached to each deoxyribose
sugar.sugar.
Two strands are held together by nitrogenous bases on the opposite Two strands are held together by nitrogenous bases on the opposite
sides.sides.
The hydrogen bonds are specifically between Adenine & Thymine & The hydrogen bonds are specifically between Adenine & Thymine &
between Guanine & Cytosine (A-T), (G-C).between Guanine & Cytosine (A-T), (G-C).
Thus A-T form one complementary base pair strand & G-C forms Thus A-T form one complementary base pair strand & G-C forms
another.another.

7. A=T are joined by two weak hydrogen bonds & G C are by three.A=T are joined by two weak hydrogen bonds & G C are by three.
Purines are large, while Pyrimidines are smaller molecules hence, Purines are large, while Pyrimidines are smaller molecules hence,
the parallel strands are twisted.the parallel strands are twisted.
A characteristic feature is that the protein called “Histone” absent in A characteristic feature is that the protein called “Histone” absent in
“Prokaryotes” but present in “Eukaryotes”.“Prokaryotes” but present in “Eukaryotes”.
Thus arrangement on one strand is T-C-G-A-T-C & arrangement on Thus arrangement on one strand is T-C-G-A-T-C & arrangement on
another strand is A-G-C-T-A-G.another strand is A-G-C-T-A-G.
Therefore A+T/ G+C = Constant for a particular species.Therefore A+T/ G+C = Constant for a particular species.
During replication of DNA molecule, the 2 strands separate at one During replication of DNA molecule, the 2 strands separate at one
end & each strand act as a end & each strand act as a Template Template for the synthesis of other for the synthesis of other
complementary strand, to form double helix.complementary strand, to form double helix.

8. DEOXYRIBOSE
PHOSPHAT
E
DEOXYRIBOSE
PHOSPHAT
E
DEOXYRIBOSE
ADENINE
GUANINE
CYTOSINE GUANINE
CYTOSINE
THYMINE
DEOXYRIBOSE
PHOSPHAT
E
PHOSPHAT
E
DEOXYRIBOSE
PHOSPHAT
E
DEOXYRIBOSE
DOUBLE STARANDED DNA
ONE STRAND ANOTHER STRAND

9. RNA is usually single stranded. RNA is usually single stranded.
Structurally similar to that of DNA.Structurally similar to that of DNA.
Except for 2 differences = Except for 2 differences =
A. A. Sugar “Ribose” present instead of Sugar “Ribose” present instead of
“Deoxyribose”.“Deoxyribose”.
B.B. Nitrogen base “Thymine” is replaced by “Uracil”. Nitrogen base “Thymine” is replaced by “Uracil”.
Three different types of RNA – Three different types of RNA –
A. Messenger RNA (mRNA).A. Messenger RNA (mRNA).
B. Ribosomal RNA (rRNA).B. Ribosomal RNA (rRNA).
C. Transport RNA (tRNA).C. Transport RNA (tRNA).
For example A-U-C-GFor example A-U-C-G
U-A-G-CU-A-G-C
RNA structureRNA structure (Ribose Nucleic Acid (Ribose Nucleic Acid
) )

10. IMPORTANT DEFINATIONS IMPORTANT DEFINATIONS
GENEGENE – – A segment of DNA that specifies for a particular A segment of DNA that specifies for a particular
polypeptide is called a “GENE”.polypeptide is called a “GENE”.

CODONCODON – – Genetic information is stored in DNA as a code.Genetic information is stored in DNA as a code.
Codon consist of sequence of three nucleotide bases i.e. the Codon consist of sequence of three nucleotide bases i.e. the
code is triplet.code is triplet.
Each codon specifies for production of a single amino acid.Each codon specifies for production of a single amino acid.
 But more than one codon may exist for the same amino acid.But more than one codon may exist for the same amino acid.

For e.g.- AGA codes for Arginine & CGU, CGC, CGA, & AGG For e.g.- AGA codes for Arginine & CGU, CGC, CGA, & AGG
can also code for the same amino acid, Arginine. can also code for the same amino acid, Arginine.

11. NON SENSE CODON –NON SENSE CODON –
Three codons (UAA, UGA, & UAG) do not code for any Three codons (UAA, UGA, & UAG) do not code for any
amino acid & act as a “ Stop codon” for terminating the amino acid & act as a “ Stop codon” for terminating the
message for the synthesis of a polypeptide. These are message for the synthesis of a polypeptide. These are
known as known as “Nonsense codons”. “Nonsense codons”.
ANTICODONS -ANTICODONS - The word anticodon used in The word anticodon used in
connection with tRNA. connection with tRNA.
This is specific for nitrogen base triplet known as This is specific for nitrogen base triplet known as
Recognition site placed on the exposed part of tRNA.Recognition site placed on the exposed part of tRNA.
It is complementary to codon on mRNA with which it It is complementary to codon on mRNA with which it
associates during protein synthesis.associates during protein synthesis.
IMPORTANT IMPORTANT
DEFINATIONS DEFINATIONS

12. SYNTHESIS OF POLYPEPTIDE SYNTHESIS OF POLYPEPTIDE
Genetic information in DNA, transcribed on to RNA & then Genetic information in DNA, transcribed on to RNA & then
translated as the particular polypeptide.translated as the particular polypeptide.

13. TRANSCRIPTION TRANSCRIPTION
Transfer of genetic information from a DNA to mRNA.Transfer of genetic information from a DNA to mRNA.
Part of DNA unzipped by breaking HPart of DNA unzipped by breaking H
2 2 bond only one of the bond only one of the
strand is used asstrand is used as “Template” “Template” for for synthesis of mRNA.synthesis of mRNA.

In synthesis of mRNA thymine is replaced by Uralic.In synthesis of mRNA thymine is replaced by Uralic.

mRNA synthesis takes place in presence of enzyme “RNA mRNA synthesis takes place in presence of enzyme “RNA
polymerase” following pairing of A=U & C G.polymerase” following pairing of A=U & C G.
Role of mRNARole of mRNA is acting as is acting as “Messenger”. “Messenger”.
It carries transcribed information from DNA to Ribosome, the It carries transcribed information from DNA to Ribosome, the
actual site of protein synthesis. This process is called as actual site of protein synthesis. This process is called as
“Transcription”.“Transcription”.

14. TRANSLATION TRANSLATION
This is actual process of protein synthesis, takes place in This is actual process of protein synthesis, takes place in
cytoplasm on ribosome.cytoplasm on ribosome.
The mRNA passes into cytoplasm & then mRNA & tRNA The mRNA passes into cytoplasm & then mRNA & tRNA
come together on surface of ribosomes containing rRNA is come together on surface of ribosomes containing rRNA is
known as “Codon”. known as “Codon”.
The base sequence on mRNA are recognized by the The base sequence on mRNA are recognized by the
anticodon present on tRNA.anticodon present on tRNA.
The tRNA contains the triplet (anticodon) at one end & The tRNA contains the triplet (anticodon) at one end &
amino acid at other end.amino acid at other end.

15. Ribosome moves along the mRNA until the entire mRNA Ribosome moves along the mRNA until the entire mRNA
molecule has been translated into corresponding molecule has been translated into corresponding
sequence of amino acids.sequence of amino acids.
The transferred amino acids are joined by peptide bonds The transferred amino acids are joined by peptide bonds
in presence of enzymes “Peptide synthesis” present in in presence of enzymes “Peptide synthesis” present in
ribosomes.ribosomes.
This process is called as This process is called as “Translation”. “Translation”.
TRANSLATION TRANSLATION

16. The formation of polypeptide chain is terminated by one of The formation of polypeptide chain is terminated by one of
the three “Terminating codons i.e. UAG, UGA, UAA called the three “Terminating codons i.e. UAG, UGA, UAA called
as “Stop Codon” OR “Non sense Codon” . as “Stop Codon” OR “Non sense Codon” .
Which do not code for any amino acid.Which do not code for any amino acid.
The tRNA, mRNA, & ribosome are dislocated.The tRNA, mRNA, & ribosome are dislocated.
tRNA goes in cytoplasm for reuse.tRNA goes in cytoplasm for reuse.
mRNA being a labile structure get dissolved in cytoplasm, & mRNA being a labile structure get dissolved in cytoplasm, &
peptide chain is released to form protein.peptide chain is released to form protein.
Thus in protein synthesis DNA acts as an “Architect”,Thus in protein synthesis DNA acts as an “Architect”,
mRNA as “Blue print”.mRNA as “Blue print”.
tRNA as “Builders”.tRNA as “Builders”.
Which build up proteins by using amino acids as a raw Which build up proteins by using amino acids as a raw
material under the supervision of ribosomes.material under the supervision of ribosomes.
TERMINATION

17. Gene transferGene transfer
Ways that bacteria can acquire new Ways that bacteria can acquire new
genetic information - genetic information -
–Transformation -Transformation -
Taking up of “naked DNA” from solution.Taking up of “naked DNA” from solution.
–Transduction -Transduction -
Transfer of DNA one to cell to another by a virus.Transfer of DNA one to cell to another by a virus.
–Conjugation -Conjugation -
““Mating”: transfer of DNA from one bacterium to Mating”: transfer of DNA from one bacterium to
another by direct contact.another by direct contact.

18. Gene transfer between bacteriaGene transfer between bacteria
TransformationTransformation::
uptake of “naked” DNA uptake of “naked” DNA
from medium.from medium.
When Griffith did his When Griffith did his
experiment combining experiment combining
heat killed, virulent cells heat killed, virulent cells
with live, harmless with live, harmless
mutants, the living cells mutants, the living cells
took up the DNA from took up the DNA from
solution, changed into solution, changed into
capsule-producing, capsule-producing,
disease-causing disease-causing
bacteria.bacteria.

19. DNA must be homologous, so transformation
only occurs between a few, close relatives.
Transformation detailsTransformation details

20. Gene transfer between bacteria-2Gene transfer between bacteria-2
TransductionTransduction: - Transfer of DNA via a virus.: - Transfer of DNA via a virus.
More common, but
still requires close
relative.

23. Conjugation: bacterial sexConjugation: bacterial sex
Conjugation is widespread and does Conjugation is widespread and does
NOT require bacteria to be closely NOT require bacteria to be closely
related.related.
Bacteria attach by means of a sex Bacteria attach by means of a sex
pilus, hold each other close, and DNA pilus, hold each other close, and DNA
is transferred. is transferred.
Plasmids other than F plasmids, such Plasmids other than F plasmids, such
as resistance plasmids, can also be as resistance plasmids, can also be
exchanged, leading to antibiotic-exchanged, leading to antibiotic-
resistant bacteria.resistant bacteria.

24. PlasmidsPlasmids
Plasmids: Small, circular, independently Plasmids: Small, circular, independently
replicating pieces of DNA with useful, not replicating pieces of DNA with useful, not
essential infoessential info
Types of plasmidsTypes of plasmids
–Fertility, Fertility,
–Resistance, Resistance,
–Catabolic, Catabolic,
–Bacteriocin, Bacteriocin,
–Virulence, Virulence,
–Tumor-inducing, and Tumor-inducing, and
–CrypticCryptic

25. About plasmids-1About plasmids-1
Fertility plasmid: genes to
produce a sex pilus;
replicates, and a copy is
passed to another cell.
Resistance plasmid: genes
that make the cell resistant to
antibiotics, heavy metals.
Catabolic plasmid: example,
tol plasmid with genes for
breaking down and using
toluene, an organic solvent.

26. About plasmids-2About plasmids-2
Bacteriocin plasmidBacteriocin plasmid:: codes for bacteriocins, proteins codes for bacteriocins, proteins
that kill related bacteria.that kill related bacteria.
Virulence plasmidVirulence plasmid: : has genes needed for the bacterium has genes needed for the bacterium
to infect the host.to infect the host.
Tumor-inducing plasmidTumor-inducing plasmid:: The The TiTi plasmid found in plasmid found in
Agrobacterium tumefaciensAgrobacterium tumefaciens. .
Codes for plant growth hormones. Codes for plant growth hormones.
When the bacterium infects the plant cell, the plasmid is When the bacterium infects the plant cell, the plasmid is
passed to the plant cell and the genes are expressed, passed to the plant cell and the genes are expressed,
causing local overgrowth of plant tissue = gall. Very useful causing local overgrowth of plant tissue = gall. Very useful
plasmid for cloning genes into plants.plasmid for cloning genes into plants.

27. THANK THANK
YOU !YOU !