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Micro Lab 22 & 23
Physical Methods of Control: Heat & UV Radiation
| Question | Answer |
|---|---|
| Optimal growth range of about 0*C to 20*C optimum at 15*C | psychrophilic |
| Optimal growth range of 20*C to 30*C | psychrotrophic |
| Optimal growth range of 25*C to 40*C optimum at 37*C | mesophilic |
| Optimal growth range of 45*C to 65*C | thermophilic |
| Optimal growth range of about 80*C or higher | hyperthermophilic |
| most heat-resistant to UV rays | endospores |
| hot-air ovens or incineration denatures enzymes, dehydrates microbes, and kills by oxidation effects | Dry heat |
| standard application of 170*C for 2 hours is for what? | hot-air oven |
| transfers heat energy to the microbial cell more efficiently resulting in the denaturation of enzymes - includes pasteurization, boiling, and autoclaving | Moist heat |
| temperature maintained at 63*C for 30 minutes or 72*C for 15 seconds to kill designated organisms that are pathogenic or cause spoilage | Pasteurization |
| 100*C for 10 minutes will kill vegetative bacterial cells but does not inactivate endospores | Boiling |
| most effective method of moist heat sterilization - use of steam under pressure - 120*C for 15 minutes at 15 psi | Autoclaving |
| the length of time required to kill all bacteria in a liquid culture at a given temperature - | Thermal death time (TDT) |
| the temperature require to kill all bacteria in a liquid culture in 10 minutes - less common | Thermal death point (TDP) |
| the time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed | Decimal reduction time (DRT, or D value) |
| Radiation that differs in wavelength and energy | radiant energy spectrum |
| X-rays and gamma rays are forms of what kind of radiation? | ionizing radiation |
| principle effect is to ionize water into highly reactive free radicals (with unpaired electrons) that can break strands of DNA. | X-rays and gamma rays |
| nonionizing radiation between 15 and 400 nm | ultraviolet (UV) |
| wavelengths essential fro biochemical processes | nonionizing |
| most lethal wavelengths, sometimes called biocidal, are in the range of 200 to 290 nm and correspond to the optimal absorption wavelengths of DNA | UVC |
| wavelengths range of 290-320 nm and can also cause damage to DNA | UVB |
| wavelengths range of 320-400 nm and not as readily absorbed and are therefore less active on living organisms | UVA |
| induces thymine dimers in DNA which result in a mutation | Ultraviolet light |
| when thymine dimers are exposed to visible light what are activated that split the dimers restoring the DNA to its undamaged state - what is this called? | photolyases; light repair or photoreactivation |
| another repair mechanism independent of light where dimers are removed by endonuclease, DNA polymerase replaces the nucleotides, and DNA ligase seals the sugar-phosphate backbone. | dark repair |
Created by:
hollieritter
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