1. Bacterial genetics lec. No.5
Lectures of D.r Oruba khalid

2. Bacterial genetics Genetics define & analyze heredity
Bacterial genetics Genetics define & analyze heredity. The unit of heredity is the gene which is a segment of DNA that carries information for specific biochemical or physiological properties. Each characteristic of bacteria is controlled by a specific gene. DNA:- genetic information which is stored as a sequence of bases in deoxyribonucleic acid (DNA).

3. DNA Structure Double stranded Nucleotide Base Pairs
Nitrogen Bases
Sugar
Phosphate
Base Pairs
Hydrogen Bonds
A-T
C-G
Alpha helix
5’ – phosphate group
3’ – hydroxyl group

4. The complementary bases enable one strand to provide the information for copying or expression of information in other strand. Each base determines the genetic information of DNA. DNA is a circular single closed loop found in the cytoplasm of bacteria. This DNA carries the gene.

5. Genes present along the circle of DNA
Genes present along the circle of DNA. Number & location of gene on DNA differ from one bacterium to another. Some bacteria have several hundreds or thousands of genes. GENOME:- is a complete set of genes (more than one gene that carry the information & characters of microorganisms). Genome also can be identified as the totality of genetic information in the organism.

6. Chromosome function (protein synthesis):- In protein synthesis there is: DNA transcription mRNA translation Protein Each amino acid has at least a triplet bases for each codon. • There is an anticodon which is complementary to the codon for example codon UGG has anticodon ACC. • Codon: is a sequence of three bases that determine the structure of one amino acid. • The types of RNA in bacteria & any cell are : (1) mRNA (2)tRNA (3)rRNA.

9. 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)

10. 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

11. 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

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

13. Plasmids

14. Conjugation
Plasmids
extrachromosomal circular DNA, M.W Daltons
Not very necessary to the cell, but add selective advantage over other organisms
May be lost from the cell under environmental stress, such as: changes in temperature, presence of certain dyes, or nutrient depletion.
Plasmid replication occur during cell division and during conjugation.
Presence of certain plasmids possesses the properity of conjugation, therefore called conjugative plasmids.
Non-conjugative plasmids may get transferred at the same times with the conjugative plasmids in a process called plamid mobilization
Certain plasmids are stably inherited called ( compatible plasmids), others are lost after few divisions called( non compatible plasmids)

15. Conjugation
Sex

16. Plasmid F-factor F = fertility ~25 genes Sex Pilus
F+ = male
F- = female
~25 genes
Sex Pilus
Replicates in synchrony with host DNA
Rolling method
DNA replicates from parent
If integrated with host DNA becomes Hfr

17. R-plasmids (resistance plasmids) responsible for resistance to drug
Classes 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

18. During the process of conjugation, the sex pilus, which is formed due to stimulation by the conjugative plasmid, the sex pilus is attached to the reciepent cell on a special receptor, where the tip of the pilus leads to lyses of a tiny area on the recipent cell wall. Attachment will stimulate the plasmid to replicate where a single strand is and the other remains in the donor cell where another complementary strand is synthesized. The receipent cell will have the same extra character possessed by the donor cell. The pilus is cut off of unknown reason.

19. 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.