Lecture 5. GENETICS OF PROKARYOTES 1. Basic concepts 2. The prokaryotic genome 3. The pan-genome 4. Genetic interchange and recombination 4.1. Recombination 4.2. Transformation 4.3. Conjugation 4.4. Transduction 5. Transposable elements 6. Genetic manipulation of microorganisms ( Genetic engineering )
1. BASIC CONCEPTS Genome: molecule/s storing the genetic information (DNA in all cells; DNA and/or RNA in viruses) Gene: the basic unit of genetic information. A fragment of DNA or RNA, including regulatory sequences, coding for a protein or RNA. Regulatory sequences 5 3 Coding sequence (ORF: open reading frame) Expression: transcription (when the gene product is a rrna or trna) or transcription and translation (when the gene product is a protein; implies mrna) Replication Transcription DNA RNA PROTEIN Translation Reverse transcription GENETIC CODE Replication
2. THE PROKARYOTIC GENOME Chromosome: carries genes essential for survival Plasmid/s: non essential* genes. Selectve advantages Chromosome Plasmids
2. THE PROKARYOTIC GENOME 2.1. CHROMOSOME Number: normally, only one Copy number: 1 100 Size: 0.5 Mb 10 Mb Structure: cccdna (with some exceptions) supercoiled Packaging: basic proteins, cations, etc. Plasmid Regulatory non-coding sequences (11%) Protein coding sequences (87%) RNA coding sequences (0.8%) Non-coding sequences (0.7%) Chromosome Escherichia coli chromosome
2. THE PROKARYOTIC GENOME 2.1. CHROMOSOME OPERON REGULON Only one promoter. Co-transcription of several genes. Polycistronic RNA One regulatory molecule Co-expression of several operons
2. THE PROKARYOTIC GENOME 2.2. PLASMIDS Circular (normally) DNA molecules Chromosome-independent replication Genes non-essential* for growths Size range from 1 Kb to 1 Mb (megaplasmids) High/low copy number Incompatibility groups Curation: plasmid loss (induced or spontaneous) Plasmid Plasmid types: Cryptic Conjugative Chromosome Resistance Metabolic Virulence Plasmids R Episome Engineered
2. THE PROKARYOTIC GENOME 2.2. PLASMIDS ROLLING CIRCLE REPLICATION
3. THE PAN-GENOME Core genome vs. Accessory genome (strain and environmental sequences)
GENETIC VARIABILITY GENETIC VARIABILITY Eukaryotes: Prokaryotes: Individual level (mutation and recombination) Population level (sexual reproduction) Individual level (mutation and recombination) Population level (HGT: horizontal gene transfer or LGT: lateral GT)
These mechanisms transfer DNA to receptor cells. This DNA will stay if it recombines with the receptor genome
4.1. RECOMBINATION Together with point mutations, this is a mechanisms of generating genetic diversity Transfer of DNA between different molecules. Homologous recombination requieres large straches of homologous sequences (>100pb)
4.1. RECOMBINATION Barrier to the recombination: restriction-modification systems Exogenous DNA Methylase Restriction enzyme CH 3 Methylated Chromosomic DNA CH 3
4.1. RECOMBINATION RESTRICTION ENZYMES
4.1. TRANSFORMATION
4.1. TRANSFORMATION Definition? Competent cells Viral DNA: transfection DNA binding proteins Autolysines Nucleases DNA carrier proteins
4.1. TRANSFORMATION Natural or recombinant plasmid (Genetic Engineering)
4.1. CONJUGATION
4.1. CONJUGATION DNasa
4.1. CONJUGATION Conjugative plasmids [e.g.: plasmid F (factor F)] F+ F- F+ F+
4.1. CONJUGATION Integration into the genome (episomes) Plasmid F Chromosome Plasmid F INtegrated plasmid F bbe
4.1. CONJUGATION
4.1. CONJUGATION
4.1. CONJUGATION From Hfr to F- From F to F- 2 recombinat cells 2 cells with F
4.4. TRANDSUCTION DNase
4.4. TRANDSUCTION LYTIC vs LYSOGENIC CYCLES Virulent phages Always lysis Temperate phages Integration/Lysis
4.4. TRANSDUCTION GENERALIZED TRANSDUCTION Defective phage Transduced cell
SPECIALIZED TRANSDUCTION
4.4. TRANSDUCTION Gene Transfer Agents (GTAs)
5. TRANSPOSABLE ELEMENTS DNA fragments that can move and integrate in a new genomic region (transposition) Insertion sequences Transposons Replicative transposons
5. TRANSPOSABLE ELEMENTS CUT AND PASTE Genomic region A (with a mobile element) Genomic region B (without a mobile element) Transposable element Transposable element Genomic region A (without a mobile element) Genomic region B (with a mobile element) COPY AND PASTE Genomic region A (with a mobile element) Genomic region B (without a mobile element) Transposable element Transposable element Genomic region A (with a mobile element) Genomic region B (with a mobile element)
5. TRANSPOSABLE ELEMENTS 5 3 5 3 Gene expression inactivation 5 P Over-expression 3 No effect 5 3
6. GENETIC MANIPULATION OF MICROORGANISMS 6.1. GENE CLONING Restriction enzymes / Taq polimerase Restriction enzymes DNA ligases bb Transformation
6. GENETIC MANIPULATION OF MICROORGANISMS 6.2. CLONING VECTORS BBE
6. GENETIC MANIPULATION OF MICROORGANISMS 6.2. CLONING VECTORS
6. GENETIC MANIPULATION OF MICROORGANISMS 6.3. METAGENOMICS