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Bacterial Genetics.PPTX
- 2. contents • NUCLEIC ACID STRUCTURE VE ORGANIZATION Nucleotide structure and sequence Molecular structure of DNA Gene and genetic code Chromosome Extrachromosomal elements of genome • REPLICATION AND EXPRESSION OF GENETIC INFORMATION Replication Expression of genetic information o Transcription o Translation (initiation-elongation-termination) o Regulation and control of gene expression • GENETIC EXCHANGE AND DIVERSITY Mutation Genetic recombination (homologous- nonhomologous) Genetic exchange oTransformation oTransduction oConjugation
- 3. Bacterial genetics • The ability of a microorganism to maintain viability, to adapt, to multiply, to cause disease is determined by the organism’s genetic composition.
- 5. GENOMIC STRUCTURE Nucleic acids DNA • Double helix, antiparallel chains • Base sequence=genetic code • Provide the format essential for consistent replication and expression of the genetic code. RNA • It is found as a single strand • There are three types of RNA inside the cell mRNA tRNA rRNA
- 6. Genomic structure CHROMOSOME • Haploid chromosome • Circular, closed double helix DNA, super coiled structure • Essential and non essential genes are here (for all the metabolic activities;reproduction,replication..) • ~2000-4000 genes • In Haemophilus influenza, it is detected 1,830,137 base pairs for 1743 genes. • It is found as a single copy.
- 7. Composite Transposons They have antibiotic resistance genes, They can integrate to plasmid or chromosome. Plasmid Transposoble elements Pieces of DNA that move from one genetic element to another, from plasmid to chromosome or vice versa. • Simple transposons (Insertion sequences) • Composite transposans Closed, circular structure,(1,5 - 120 kb) 1/10 of bacterial chromosome Able to replicate independently and contain many copies It can carry genes of toxines, antimicrobial resistance or genes that enable plasmid to replicate and transfer.
- 8. Replication and expression of genetic informatioon During the replication; 1. Unwinding or relaxation of the chromosome’s supercoiled DNA 2. Separation of the double helix of the parental DNA so that each strand may serve as a template 3. Synthesis of the new DNA strands 4. Termination of replication, releasing two identical chromosomes, occur sequentially.. Replication • results in the production of two identical daughter cells • mediated by various enzymes, such as DNA polymerase and cofactors, • must occur quickly and accu- rately.
- 9. Expression of genetic information=protein synthesis Protein synthesis occurs in two step: 1. Transcription 2. Translation What to need? a DNA template representing a single gene or cluster of genes various enzymes and cofactors RNA molecules of specific structure and function.
- 10. transcription • Synthesis of mRNA from DNA, • takes place in cytosol, • RNA polymerase is used, • Transcription proceeds in a 5’ to 3’ direction, • the TTP(thymine) of DNA is replaced with UTP (uracil).
- 11. translation the genetic code in mRNA molecules is translated into specific amino acid sequences that are responsible for protein structure and function code is found in sense strand of DNA codon is in mRNA every codon includes 3 nucleotides those encodes a spesific amino acid
- 12. Translation Steps Initiation • fmet • Ribosomal subunits • Various initiation factors • mRNA • AUG is the most common START codon and it codes for the amino acid formyl methionine (fMet) in prokaryotes 1. Initiation 2. Elongation 3. Termination They assembly at the ribosomal binding site on mRNA and form a complex.
- 13. • Elongation • in a 5’ to 3’ direction, • Each aa binds to its specific tRNA by aminoacyl tRNA synthetase. • Peptide bonds are formed between adjacent amino acids. Termination • When ribosomal A site encounters a stop or nonsense codon • protein synthesis complex disassociates Posttranslational modifications Folding, Enzymatic trimming
- 14. Regulation and Control of Gene Expression Physiologic balance is maintained. Transcriptional, translational, or posttranslational Transcriptional control of gene expression Repression If the gene product synthesized in anabolic reactions is excessive, it plays a repressive role on transcription.
- 15. Induction Transcription does not always occur in the gene region that codes for an enzyme used in catabolic reactions; If the substrate to be degraded increases, it binds to the repressor and enables transcription to occur. essential genes They encode products necessary for life. There is no suppressive or triggering regulation here.
- 16. Genetic mechanisms that provide diversity MUTATION A change in the original nucleotide sequence of a gene or genes belonging to an organism... Why does mutation occur???? spontaneous 10-7- 10-11 may occur frequently. Induced mutation Chemical, acridine.. Physical…UV rays Biological factor.. insertion of a foreign DNA into cell
- 17. After a mutation The microorganism may die; lethal mutation It may be nothing; silent mutation Phenotypic change may occur advantage gaining a disadvantage Is it permanent temporary?? Can it be repaired?
- 18. Genetic recombination Homologous recombination The translocated segments generally have nucleotide sequence homology to each other. REC A protein plays an essential role, Various binding proteins are involved. Occurs between dissimilar sequences. Insertions, deletions or both occur.
- 19. Gene exchanges 1-Transformation A bacterial cell (competent bacterium) can take DNA fragments from another bacterium into the cell because the DNA of another bacterial cell is found in fragments in the environment, and thus gene exchange occurs.
- 21. 2-Transduction It is caused by viruses that infect bacteria called bacteriophages
- 22. Let’s intervene!!! Bacteriophage Bacteriophage, in its virulent and mild forms, causes lytic and lysogenic cycles in bacteria.
- 23. 3-Conjugation Ensuring gene exchange among bacteria by their sex pili.
Editor's Notes
- Additionally, the dedicated base pairs provide the format essential for consistent replication and expression of the genetic code.
- Genetik materyalin yapı ve organizasyonu Genetik bilginin replikasyonu ve ifadesi Genetik bilginin değişimi ve bakteriler arası değiş- tokuşa sebep olan mekanizmalar Genetikte incelenmeli
- İnsersiyon dizileri hareketi sağlayan genleri içerirler. Transposable elements are pieces of DNA that move from one genetic element to another, from plasmid to chromosome or vice versa. Unlike plasmids, they are unable to replicate independently and do not exist as separate entities in the bacterial cell. The two types of transposable elements are the simple transposon or insertion sequence (IS) and the composite transposon. Insertion sequences are limited to containing the genes that encode information required for movement from one site in the genome to another. Composite transposons are a cassette (grouping of genes) flanked by insertion sequences. The internal gene imbedded in the insertion sequence encodes for an accessory function, such as antimicrobial resistance. Plasmids and transposable elements coexist with chromosomes in the cells of many bacterial species. These extrachromosomal elements play a key role in the exchange of genetic material throughout the bacterial microbiosphere, including genetic Exchange among clinically relevant bacteria.
- 1.Unwinding or relaxation of the chromosome’s supercoiled DNA 2. Separation of the complementary strands of the parental DNA so that each may serve as a template (i.e., pattern) for synthesis of new DNA strands 3. Synthesis of the new (i.e., daughter) DNA strands 4. Termination of replication, releasing two identical chromosomes, one for each daughter cell
- The overall process of gene expression is composed of two complex steps, transcription and translation Gene expression requires various components, including a DNA template representing a single gene or cluster of genes, various enzymes and cofactors, and RNA mole- cules of specific structure and function.
- Promotör bölgede αββ’ ünitesi çift sarmal yapıyı açar. In bacteria, the mRNA molecules that result from the transcription process are polycistronic, that is, they encode for several gene products. Frequently, polycis- tronic mRNA may encode several genes whose products (proteins) are involved in a single or closely related cel- lular function. When a cluster of genes is under the control of a single promoter sequence, the gene group is referred to as an operon.
- the code consists of triplets of nucleotide bases, referred to as codons; each codon encodes for a specific amino acid. Because there are 64 different codons for 20 amino acids, an amino acid can be encoded by more than one codon (Table 2-1). Each codon is specific for a single amino acid.
- Initiation begins with the association of ribosomal subunits, mRNA, formylmethionine tRNA ([f-met] carrying the initial amino acid of the protein to be synthesized), and various initiation factors AUG is the most common START codon and it codes for the amino acid methionine (Met) in eukaryotes and formyl methionine (fMet) in prokaryotes
- most proteins must undergo modification, such as folding or enzymatic trimming
- This strategy pre-vents waste and overproduction of products that are already present in sufficient supply. In this system, the product acts as a co-repressor that forms a complex with a repressor molecule. In the absence of co-repressor product (i.e., gene product), transcription occurs
- tek bir dna bazında farklılık Tek bir Gende farklılık Birden fazla gende farklılık Spontan mutasyon replikasyon esnasında spontan mutasyon
- kAlıcı mutasyon bir nesilden diğerine hücre genotipin entegre bir parçası olarak aktarılırsa kalıcı… Tamir edilebelir dna tamir mekanizmaları ile tamir edilebilirse Geçici spontan olarak replikasyon döngüleri devam ettikçe kaybolma durumu
- Farklı kaynaklardan gelen nükleotitlerin kombine edildiği veya yeniden yeniden birleşmenin sağlandığı mekanizma. Rekombinasyon ökaryotlarda mayozla gerçekleşen süreç Bakteride bu süreç sınırlı ama kromozomda zincir kırıkları varsa ve dışardan gelen rekombinan dna kaynağı varsa rekombinasyon gerçekleşir. Non- homolg rek için bölge spesifik rekombinasyon enzimleri gibi özelleşmiiş rekombinasyon enzimleri gerekir. (bakteriyofaj ve transpozonların sahip olduğu gibi)
- Neisseria, Haemophilus ve Streptococcus türleri arasında yaygın
- Griffith’in transformasyon üzerine yaptığı deney, streptococcus pneumonia bakterisinin kapsüllü ve kapsülsüz suşları ile yapılan deney
- faj ,Virüs kendi dnasını bakteri kromozomuna entegre eder. Replikasyonla sonrası viral ürünler de üretildiğinde kromozomdan ayrılır ve protein kılıflar içine paketlenir. Bakteri hücresi liz oluca bakteri genomundan da bir kısım DNA’yı beraberinde götürür.
- In the F+, the two strands of the double helix of the Fertility (F) factor (a plasmid) separate. 2. One of the two strands moves into the recipient (F-) cell. 3. The other strand remains in the donor cell. 4. Both strands are replicated, with clockwise rotation of the circles. 5. Both the donor and the recipient cells are now F+ after conjugation