1. Lectures of Dr. Oruba khalid
BACTERIAL GENETICS
Lectures of Dr. Oruba khalid

2. Key Words Genetics Bacterial genetics Mutation & its types
Bacteriophage
Mechanisms of gene transfer
Transformation
Transduction
Lysogenic conversion
Conjugation

3. Bacterial Genetics Genetics is the study of heredity and variation.
The unit of heredity is gene, which is a segment of DNA specifying for a particular polypeptide.
Introns - non coding sequences on a gene.
Exons - coding sequences on a gene translated into gene products.
Bacterial genetics is used as a model to understand DNA replication, genetic characters, their changes & transfer to next generations.

4. Nucleic Acids
DNA ( deoxy ribonucleic acid ) : stores information for protein synthesis.
RNA ( ribonucleic acid ) : transcription & translation of information for protein synthesis.
Central Dogma : DNA RNA Protein

5. Structure Of DNA Proposed by Watson & Crick. Double helix model.
Composed of 2 chains of polypeptides, each chain has a backbone of deoxyribose sugar and phosphate residues arranged alternately.
4 nitrogenous bases: Adenine (A) Purine
Guanine (G)
Thymine(T) Pyrimidine
Cytosine (C)

6. Double helical structure of DNA by Watson & Crick

7. DNA DNA is copied by DNA polymerase In the 5  3 direction
Initiated by an RNA primer
Leading strand synthesized continuously
Lagging strand synthesized discontinuously
Okazaki fragments
RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase

8. DNA
Figure 8.6

9. Replication of this DNA molecule always starts at a certain point (the origin of replication) and it is “semi-conservative” meaning that one strand in each of the two resulting double strands is conserved .

10. DNA Replication:
-The identical duplication process of DNA is termed semi-conservative because the double strand of DNA is opened up during replication and each strand serves as the matrix for synthesis of a complementary strand. Thus each of the two new double strands “conserves” one old strand.
-The doubling of each DNA molecule begins at a given starting point called origin of replication. This process continues throughout the entire cycle.

12. DNA
DNA replication is semiconservative
Figure 8.7

13. Translation mRNA is translated in codons (3 nucleotides)
Translation of mRNA begins at the start codon: AUG
Translation ends at a STOP codon: UAA, UAG, UGA
Figure 8.2

14. The Genetic Code
Figure 8.9

15. Structure Of RNA Structurally similar to DNA, except for 2
major differences:
ribose sugar
uracil in place of thymine.
3 types of RNA
m RNA (messenger RNA)
t RNA ( transfer RNA )
r RNA ( ribosomal RNA )

16. Genetic Information In Bacteria
Chromosome
Carries properties like virulence, pathogenicity & resistance
Plasmid
Extrachromosomal genetic material in the cytoplasm
Replicate independently
Bacteriophage
Virus infecting bacteria

17. PLASMIDS Circular DNA molecules
Important vectors in genetic engineering
EPISOME
Plasmid DNA integrated with chromosomal DNA.
Types of plasmids
R plasmid (drug resistance): RTF + r determinant
F plasmid (maleness )

18. R-plasmids (resistance plasmids) responsible for resistance to drug
Types of plasmids
Sex factor plasmids: the cell that possess this plasmid is called F+, male or the donor cell, while the one that do not possess it is called; F-, or the recipient cell.
R-plasmids (resistance plasmids) responsible for resistance to drug
Col- plasmids: responsible for production of bacteriocins.
Heavy metal ion resistant plasmids: responsible for resistance to heavy metal ions that the bacteria may get exposed in the envirnment
Plasmids of catabolic activity: responsible for degredation of highly complex compounds, such as: hydrocarbons
Virulence plasmids: reponsible for production of certain virulence factors such as: toxin , hemolysin, adhesive factors,… etc
Genetic Engineering

19. Mechanisms Of Genetic Variations
Mutation
Transfer or exchange of genetic material
Transformation
Transduction
Conjugation
Lysogenic conversion
Transposition

20. Genotype: is the gatalogue of gene arranged on the DNA molecule.
Phenotype: the collection of characters as result of the expression of these genes.
Mutation: hereitiditary changes occur in the genotype which may or may not lead to phenotypic change.

21. The physical or the chemical agent that leads to mutation is called mutagen, and the bacteria produced with such genotypic change are called mutants.
Mutation occur either spontaneously or by induction.
Induced mutation occur as a result of the effect of one of the followings:

22. A-Physical: such as U.V. light, X-ray…etc.
B-chemical:such as 5-bromouracil, nitrous acid, hydroxylamine, nitrogen mustard,
acridines, nitrosoguanidine… etc.
C-Biological: such as transposons.

23. A B C D E F G______________A B C D F G
Types of mutations:
Deletion mutation: this result in the loss of a piece of DNA.
A B C D E F G______________A B C D F G
2. Inversion mutation:this result in recombining the cut piece in revese order.
A B C D E F G_____________A B C E D F G

24. 3. Insertion mutation: a totally new base sequence is synthesized and inserted in the DNA molecule.
A B C D E F G_____________A B C K D E F G
4. Substitution mutation: a newly different base sequence is synthesized instead of the lost one
A B C D E F G______________A B C N E F G
5. Duplication mutation: an insertion of a base sequence similar to a sequence already existed.
A B C D E F G______________A B C D B E F G

25. Bacterial genetics Experiments by Nature of the genetic material
Griffith (1928); working on S- forms and R-forms of the strep. Pneumonia
Avery (1944); mixing DNA extract of the S-forms with and without Dnase, then mixing it with R-forms
Hershy and Chase (1952), used radioactive isotops on bacteriophages (S25-for head protein ) and (P32- for nucleic acids)

26. Gene transfer: Recepient
Recombination ; is the reassortment of nucleotide sequences within the DNA molecule
Recombination may occur between
Donor
Recepient
Chromosomal DNA
Plasmid DNA
Viral DNA

27. Sometimes rearrangement occurs within the DNA molecule itself without an external DNA
Any recombination or spontaneous rearrangement leads to what is called genotypic change, this may or may not leads to phenotypic change
The fate of the transferred DNA depends on:
Its capability to be taken by the host cells
Its stability within the host chromosome

28. There are three mechanisms for gene transfer in bacteria
Transformation
Conjugation
Transduction

29. Transformation (Griffith, 1928)
Transfer of genetic information by free DNA. i.e. by direct uptake of donor DNA by the recipient DNA.
Live noncapsulated (R) pneumococci + heat killed capsulated (S) pneumococci
Injected into mice
Death of mice
Live capsulated pneumococcus isolated from the blood of mice.

31. Transduction
It is the transfer of DNA from a donor to a receptor with
the help of transport bacteriophages.
Bacteriophages
Infection of another bacterium
Transfer of host bacterial DNA to the new bacterium
Acquisition of new characteristics coded by the donor DNA.

32. Bacteriophage replication occur in 5 stages:
Adsorption: where the virus is adsorped on specific receptor on the bacterial cell wall.
Penetration: the virus make a hole in the bacterial cell wall using its core and its DNA is passed through this hollow core to inside the bacteria
Replication : the viral nucleic acid controls the bacterial cell activity and mechanisms for its benefit and synthesize several numbers of the viral parts.
Maturation : during this stage, each head of a virus will be surround one part of the viral DNA, then the other parts will be joined to each other forming several numbers of viruses.
Release : finally the virus release a lysozyme that leads to cell lysis and the release of the viruses, then each virus will infect other bacteria, and so on until the lysis of the whole colony.

34. Bacteriophages Definition:-
Bacteriophages are viruses that infect bacteria . They are therefore obligate cell parasites. They possess only one type of nucleic acid, either DNA or RNA, have no enzymatic systems for energy supply and are unable to synthesize proteins on their own.
Morphology:-
Similar to the viruses that infect animals and
vary widely in appearance.

35. Transduction Transfer of bacterial genes via viruses Types
Donor to recipient
Virus: Bacteriophages
Types
Generalized
Specialized
Replication Cycle
Lytic
Lysogenic

36. Composition:
Phages are made up of protein and nucleic acid. The proteins form the head, tail, and other morphological elements, the function of which is to protect the phage genome.
The nucleic acid in most phages is DNA, which occurs as a double stranded DNA .

37. Sometimes, the recombination of the viral DNA with the chromosomal DNA may lead to a drastic change in the character of the bacteria, such as becoming a powerful toxin producer (e.g. Clostridium botulinum,, Corynebacterium diphtheriae… etc).
The bacteria are called Lysogenic cell, and the process is called Lysogenic conversion

39. 2. Conjugation
It is the transfer of DNA from a donor to a receptor in a
conjugation process involving cell-to-cell contact.
Conjugation is made possible by two genetic elements:
the conjugative plasmids and the conjugative pilli .
Conjugation is seen frequently in Gram-negative rods
(Enterobacteriaceae), in which the phenomenon has been
most thoroughly researched, and enterococci

41. Transposon (Jumping Genes, Barbara McClintock)
Plasmid
Chromosome
Transposon
DNA segment that can move between chromosome & plasmids
Insertion of transposon into a functional gene would destroy the function of the gene (internal mutagenic agents)
Transposons are not self replicative, they depend on chromosomal or plasmid DNA for replication

42. Genetic Engineering – a combination of methods which allows to conduct artificial recombination of DNA and produce chimerical molecules, non-typical for nature

43. Steps in
DNA from any desired source is cleaved into fragments by restriction endonuclease.
The fragments are spliced into vector such as plasmid or viral genome.
By transformation, the vector is introduced into a host cell in which it can replicate.
- After replication of the vector & amplification of the original DNA fragment, vector is isolated.
The inserted fragment is cleaved back out & purified.
see fig.

44. Recombinant DNA

45. Application of of genetic engineering (molecular cloning):-
Gene structure \mapping \function e.g. globin.
Biosynthesis e.g. insulin, GH (growth hormone), interferon.
Control of genetic disease.
Using PCR in detection & identification of specific organism e.g. detection of HIV by PCR.
Gene therapy.
NOTE: the field of genetic engineering (molecular cloning) involves the introduction of new genes into the cells.

46. References:
1- Jawetz, Melnick, & Adelberg’s.( 2013). Medical Microbiology (Twenty-Sixth Edition).
2- Kenneth Todar. (2008).Todar’s Online Textbook of Bacteriology ,University of Wisconsin.