Lecture 2 Bacteria And Viruses

Question 1

Why use bacteriophage in genetic study

Answer 1

Homosapiens 24 chromosome, drosophila 5 and bacteriophage only 1. No mito/chloro DNA / fast growth & repro/ easy to grow in lab & small workspace required. Natural DNA transfer mechanisms can be used to ‘map’ genes. Can be used to deliver DNA for experiments e.g. in cloning.

Question 2

Nucleoid

Answer 2

Name given to bacterias one circular chromosome - bacteria may also have plasmids. Plasmid or nucleoid start to replicate at origin of replication (ori site) both strands separate and replicate in both directions eventually create 2 identical daughter plasmids w/one original and one new strand

Question 3

Topoisomerase

Answer 3

Hoists ds DNA around it’s own axis forming supercoils and cutting it where needed. From relaxed to pos. Supercoil: adding two turns and over rotating or neg super cool: removing 2 turns underrotating

Question 4

Growing bacteria in lab

Answer 4

Inoculate sterile medium w/ bacteria and allow to grow/ divide then use pipette to apply some to agar growth medium in Petri dish. Spread evenly w/glass rod and allow to incubate 1-2 days so bacteria form colonie

Question 5

Selection medium - identify mutants

Answer 5

Grow bacteria on medium containing leu+ and leu- . Use a ‘handle’ to replica plate the colonies by transfer on the velvet surface (like a stamp.) Press onto new Petri plates one w. Leu+ & Leu - and one w/out Leu-. Mutant will not grow on medium w/out Leu- identify location of this colony by where it is missing on Petri w/out, collect colony from Petri w to culture for further study (Conclusion : colony that grows only on supplemented medium has mutant in gene encoding synthesis of an essential nutrient in this case Leu+)

Question 6

Conjugation

Answer 6

Donor bacteria connects to recipient by cytoplasmic bridge. DNA replicates and transfers to recipient cell. Crossover in the recipient cell leads to formation of a recombinant chromosome.

Question 7

Transformation

Answer 7

Ss DNA fragments taken up by a bacteria cell can exist as a plasmid or lead to crossover and recombination. When cell replicates and divides only one is transformed ( as only one of the parental strands has the recombination.)

Question 8

Transduction

Answer 8

Bacteriophage injects DNA, replicates using bacterial DNA so bacterial DNA is broken down and incorporated into phage progeny then cell lyses (pops). Phage progeny infect new bacteria w/DNA forming recombinant chromosomes.

Question 9

Cotransformation

Answer 9

DNA fragments close to one another on a genome more likely to be on the same fragment and recombined together so rate of cotransformation inversely proportional to distance between genes

Question 10

Bacteriophage virus

Answer 10

Genetic materia (DNA or RNA) in a protein coat. Virulent phages reproduce by reproduction through the lytic cycle and always kill host by lysis (popping.) Temperate phages DNA integrates I to bacterial chromosome and can remain as inactive prophage by lysogeny process.