Bacteria Reproduce Asexually via BINARY FISSION

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1 An Introduction to Microbial Genetics Today: Intro to Microbial Genetics Lunch pglo! Bacteria Reproduce Asexually via BINARY FISSION But, Bacteria still undergo GENETIC RECOMBINATION (combining DNA from two individuals into the genome of a single individual) Can this generate genetic nti diversity?!? rit?!? Genetic Recombination in bacteria occurs through three distinct processes: 1. TRANSFORMATION 2. TRANSDUCTION 3. CONJUGATION 1.TRANSFORMATION- Def: The uptake of naked, foreign DNA from the surrounding environment. The foreign DNA may be incorporated into the bacterial chromosome. Some bacterial cells have specialized surface proteins for the uptake of DNA. 1

2 2. TRANSDUCTION Def: Phage (bacterial viruses) carry bacterial genes from one host cell to another. Generalized Transduction occurs when the phage accidentally transfers random bacterial genes instead of its own. Specialized Transduction occurs when the phage takes a small adjacent region of the bacterial DNA with it. 3. CONJUGATION Def: The direct transfer of genetic material between two bacterial cells that are temporarily joined. Transfer is one-way, with the DNA donor (or male) attaching to the DNA recipient (female) with a sex pilus. The ability to form sex pili and donate DNA results from the presence of an F factor. General notes about PLASMIDS Plasmids are small, circular, self-replicating DNA molecules separate from the bacterial chromosomes. Some plasmids, like the F plasmids, can reversibly incorporate into the cell s chromosome (an episome). R PLASMIDS R plasmids contain genes conferring resistance to antibiotics. R plasmids, like F plasmids, have genes that encode sex pili and enable transfer from one cell to another. Many R plasmids carry multiple antibiotic resistance genes. 2

3 R Plasmids acquire multiple resistance genes through TRANSPOSONs. Transposon: a piece of DNA that can move from one location to another in a cell s genome. Composite Transposons include extra genes sandwiched between two insertion sequences. Composite transposons can add a gene conferring antibiotic resistance to a plasmid already carrying genes for resistance. In an environment high in antibiotics, natural selection will favor multi-drug resistant bacterial clones. Transposase catalyzes the movement of the transposon from one location to another Gene Regulation: Individual bacteria cope with environmental fluctuation at several levels: Regulation of Gene Expression occurs through OPERONS. OPERONS utilize a segment of DNA called an OPERATOR. The operator controls the access of RNA polymerase to the genes. OPERATORS function as switches to turn transcription ON or OFF. Operators are ON unless a specific REPRESSOR PROTEIN is bound to it. This operon, the trp operon is an example of a REPRESSIBLE OPERON because transcription is INHIBITED when tryptophan binds to the regulatory protein. INDUCIBLE OPERONs are STIMULATED when a specific small molecule interacts with a regulatory protein. Examples of Inducible Operons: the lac operon the ara operon 3

4 INDUCIBLE OPERONS: The lac Operon The lac OPERON is also positively regulated by cyclic AMP (camp) and the regulatory protein, camp receptor protein (CRP). Activated CRP stimulates transcription. Without camp, transcription levels are low, even in the presence of Lactose! You Try! 1.With your group, represent how the ara operon we will use in lab might work. 2. Fill-in the table provided to generate your hypothesis and predictions for your lab work this week! (Each group should turn in one sheet with their pre-lab!) What is a Virus? Obligate Intracellular Parasites! Viruses are classified according to several characteristics: Whether the genome is DNA or RNA g Whether the nucleic acid is single-stranded or double-stranded Whether the shape of the virion is simple or complex Whether the virion is surrounded by a membrane 4

5 Viral Life Cycles The Lytic Cycle Let s Watch: Switching Between Lysogenic and Lytic Cycles Requires Regulation! Sample Lifecycle: the Influenza Virus (a ss RNA Virus) An Aside: Viral Recombination Sample Lifecycle: the HIV Virus (another ss RNA Virus) Viruses Also Infect Plant Cells Plant viruses do not use membrane receptors but rather take advantage of mechanical methods to enter the cell. 5