Microb 201: Week 5 Notes
Microb 201: Week 5 Notes MICRB 201
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This 2 page Class Notes was uploaded by Grace Spellacy on Tuesday February 16, 2016. The Class Notes belongs to MICRB 201 at Pennsylvania State University taught by Dr. Steven Keating in Spring 2016. Since its upload, it has received 75 views. For similar materials see Introductory Microbiology in Microbiology at Pennsylvania State University.
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Date Created: 02/16/16
Exam 2 Info 2/8/16 Transfer of DNA from one cell to another Mechanism for acquisition of new genes Medical significance: can acquire antibiotic resistant genes or genes that can cause disease 1. First Mechanism: Transformation Transfer of DNA through open environment DNA is released from a lysed cell which produces DNA fragments Recipient cell absorbs DNA o Must be competent to absorb it o Competency may be natural or artificially induced Natural competency is observed in some species including: Bacilis, Streptococcus, Pseudomonas o Needs specific: genes, surface, receptor proteins, and stage of growth of recipient for natural competency o Uptake System: 1. Bind to DNA outside of cell (almost always linear) 2. As DNA is absorbed, one strand degrades and the other strand goes into the cytoplasm 3. Single strand in the cytoplasm aligns with homologous regions of the chromosome (the area with complement base pairs) 4. a. May fail to integrate into chromosome and degrade b. May be integrated into existing chromosomes and the cell will get new genes likelihood is related to genetic relatedness Example of Natural competency: Streptococcus pneumonae o Most common cause of pneumonia o 1920s: Fred Griffith: found two groups of strains S strain: cells are carried in a capsule, cause disease and grew in smooth colonies R strain: cells lacked a capsule, did not cause disease and grew in rough colonies Griffith wanted to know if strains changed - Combined live non capsule cells (r strain) and dead capsule cells (s strain) which killed the mice - His conclusion was that something from the s strain cells transformed the r strain cells causing them to produce a capsule and become s train - He did not know what the “factor” that transformed the cells was o 1940s: Oswald Avery: finds that “factor” is DNA through degrading DNA and finding there is no transformation to s strain Artificial Competency o Cells can be treated to increase membrane permeability through calcium chloride, electroporation (brief shock) o Cells can be genetically engineered to transfer plasmids back in cells o Double strand circles o Alter plasmids by putting genes of interest into plasmid 2. Second Mechanism: Transduction DNA transfers from donor to recipient via bacterial virus (bacteriophage) Some potential for cross species transfer Some bacteriophages infect a wide range of bacterial species, some are host specific Used in genetic engineering o Can mix DNA of interest with virus proteins o The new virus particle then has the DNA of interest inside Generalized transduction o Random process, any DNA might be in particle o Phage holds 1-2% of chromosome o Phage is released and a new phage infects another recipient cell Infects bacterial DNA o Infected DNA 1. May be degraded (if not integrated) 2. May be incorporated into the chromosome so new genes are gained and copied when cell divides Specialized transduction o Begins with lysogenic
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