Bacterial Genetics March 2015 Terminology n Genetics The
+ Bacterial Genetics March 2015
+ Terminology n Genetics: The study of what genes are, how they carry information, how information is expressed, and how genes are replicated n Gene: A segment of DNA that encodes a functional product, usually a protein n Chromosome: Structure containing DNA that physically carries hereditary information; the chromosomes contain the genes n Genome: n Plasmid All the genetic information in a cell – small circular DNA molecule that replicates independently of the chromosome
+ DNA n Polymer of nucleotides: Adenine, thymine, cytosine, and guanine n Double helix associated with proteins n "Backbone" is deoxyribose -phosphate n Strands are held together by hydrogen bonds between AT and CG n Strands are antiparallel Figure 8. 3 b
+ DNA Synthesis Figure 8. 5
+ Replication of Bacterial DNA Figure 8. 6
+ Transcription n DNA is transcribed to make RNA (m. RNA, t. RNA, and r. RNA) n Transcription begins when RNA polymerase binds to the promoter sequence n Transcription proceeds in the 5' 3' direction n Transcription stops when it reaches the terminator sequence
+ The Process of Transcription Figure 8. 7
+ Translation n m. RNA is translated in codons (three nucleotides) n Translation of m. RNA begins at the start codon: AUG n Translation ends at nonsense codons: UAA, UAG, UGA Figure 8. 2
+ Simultaneous Transcription & Translation Figure 8. 10
+ Genetic Transformation – Frederick Griffith (1920 s) Figure 8. 24
+ Recombinant DNA Technology n Recombinant DNA: DNA made from two different sources. n In the 1960 s, Paul Berg inserted animal DNA into bacterial DNA, and the bacteria produced an animal protein
+ Recombinant DNA Technology n 1941: George Beadle and Edward Tatum showed that genes encode a cell’s enzymes n 1944: Oswald Avery, Colin Mac. Leod, and Maclyn Mc. Carty showed that DNA was the hereditary material n 1961: Francois Jacob and Jacques Monod discovered the role of m. RNA in protein synthesis
+ The Flow of Genetic Information Figure 8. 2
+ Genetic Recombination n Vertical gene transfer: Occurs during reproduction between generations of cells. n Horizontal gene transfer: The transfer of genes between cells of the same generation.
+ Genetic Recombination Figure 8. 25
+ Transmission of Genetic Material in Bacterial Cells
+ Conjugation
+ Transformation
+ Transduction
+ 3 main categories of genes Structural genes • Code for proteins Regulatory genes • Control gene expression RNA coding genes
+ Operons: The Basic Concept n Operator -the regulatory “switch”, a segment of DNA n usually positioned within the promoter n Operon – (DNA) includes the operator, the promoter, and the genes that they control n In coordinate control, a cluster of functionally related genes can be controlled by a single onoff “switch”
+ Operons: Activation n Activator – (protein) when stimulated, changes shape and binds to the promoter to increase the affinity of RNA polymerase to the promoter (increasing the rate of transcription). - The lac operon is stimulated by a small organic molecule known as c. AMP that is produced in response to low cellular glucose.
+ Operon: Lactose Metabolism
+ Lac Operon: Sensing Glucose vs. Lactose Bacterial will always prefer glucose over lactose if it is available. Thus, how does E. coli sense when glucose levels are low? How does it relay that information to the genome?
+ Operons: Activation of Lac Operon n Lactose present No glucose n Lactose and Glucose present Figure 8. 15
+ Operons: Repression n Repressor – (protein) switches the operon off n Prevents transcription by binding to the operator and blocking RNA polymerase n the product of a separate regulatory gene n can be in an active or inactive form, depending on the presence of other molecules n Corepressor – cooperates with a repressor protein to switch an operon off
+ Operons: Relieving Repression n When a repressor is bound to the operator, RNA poly cannot bind the promoter and transcription is turned “off” n When the repressor is not bound to the operator, RNA poly can bind the promoter and transcription is turned “on”.
+ Biotechnology n Recombinant DNA technology, a new technique for biotechnology, enables bacteria and fungi to produce a variety of proteins including vaccines and enzymes n Missing or defective genes in human cells can be replaced in gene therapy n Genetically modified bacteria are used to protect crops from insects and from freezing
Figure 9. 11
+ p. GLO Plasmid DNA
+ Lac Operon vs Ara Operon
+ Replacing Ara operon with GFP gene
+ Bacterial Conjugation Figure 8. 26
+ Plasmids n. Conjugative plasmid: Carries genes for sex pili and transfer of the plasmid n. Dissimilation plasmids: Encode enzymes for catabolism of unusual compounds n. R factors: Encode antibiotic resistance
+ R Factor, a Type of Plasmid Figure 8. 29
+ Conjugation in E. coli Figure 8. 27 a
+ Conjugation in E. coli Figure 8. 27 b
+ Conjugation in E. coli
+ Transduction by a Bacteriophage Figure 8. 28
- Slides: 43