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Lab #33 - (Lab Quiz 4) - UV Light: Lethal Effects - Flashcards

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Class:MICR 211 - General Microbiology
Subject:Microbiology
University:California State University - Long Beach
Term:Fall 2010
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Ultraviolet (UV) Light nonionizing short wavelength radiation that falls between 4 nm and 400 nm in the visible spectrum.
In general, for electromagnetic radiation, the ___ the wavelength, the more ___ it is to cells. shorter, damaging.
UV light is much more ____ than either visible light or infrared radiation. Germicidal.
Most bacteria are killed by the effects of ___ ___. Ultraviolet light.
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____ ___ is routinely used to sterilize surfaces, such as the work areas of transfer hoods used for the inoculation of cultures. Ultraviolet light.
The primary lethal effects of ultraviolet light are due to its ___ properties. mutagenic
UV radiation at ___ is the most germicidal, and why is this the case? 260 nm, because this wavelength is the specific wavelength at which DNA maximally absorbs UV light.
When DNA absorbs UV light, it causes the formation of ___. pyrimidine dimers.
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Pyrimidine dimers These form when a covalent bond is formed between 2 adjacent thymine or cytosine molecules in a DNA strand.
What do dimers essentially cause? It causes the DNA molecule to become deformed so that the DNA polymerase cannot replicate DNA strands past the site of dimer formation, nor can genes past this point be transcribed.
Cells have evolved various ___ ___ to deal with mutational changes in DNA in order to insure that fidelity of replication occurs. repair mechanisms.
SOS system a system which systematically removes the dimers and inserts in their place new pyrimidine molecules.
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Unlike ___ ____, enzymes of the ____ ___ can move beyond the point where dimers occur in the molecule. DNA polymerase, SOS system.
However, if the exposure of UV light is sufficient to cause massive numbers of dimers to form in the DNA of a cell, why can't the SOS system cope with this situation? The SOS system is unable to effectively cope with this situation because it beings to make errors by inserting incorrect bases for the damaged bases, eventually resulting in cell death.
The killing properties of UV light depend on several factors: Time of exposure, presence of materials that will block the radiation from reaching cells (ex. plastic), endospores
What is an example of a material that would block radiation from reaching cells? Plastic can block UV radiation and plastic lenses are an effective means to protect the eyes from UV damage.
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What are 2 reasons why endospores more resistant to UV light than are vegetative cells? 1) The DNA of endospores is protected by small, acid-soluble proteins that bind to DNA and alter its conformation, thereby protecting it from photochemical damage. 2) A unique spore photo-product is generated by UV light in endospores that functions in enzymatic repair of damaged DNA during endospore germination.
Which bacterium is an endospore former used to examine the germicidal effects for UV light? Bacillus megaterium.
Which bacterium is an non-endospore former used to examine the germicidal effects for UV light? Staphylococcus aureus.
What is the objective of this experiment? To examine the germicidal effects for UV light and to compare the relative resistance of vegetative cells and endospores.
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Why was half of each plate covered with an index card? The index card blocks the UV rays and provides direct comparison to the side that is exposed.
What was the purpose of leaving the cover on one set of petri dishes? The ability of plastic, even clear, to block UV rays is demonstrated.
Describe the damaging effects of UV radiation on living cells. UV radiation causes the formation of thymine dimmers in DNA that result in replication errors during reproduction. These error cause gene defects, which ultimately lead to cell death.
Why does exposure to UV radiation cause death in vegetative cells but not endospores? Endospores are non-dividing cells and are not subject to the same effects as reproducing vegetative cells.
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At which wavelength is UV radiation most germicidal? Explain. UV radiation is most germicidal at 260 nm because that is the wavelength at which DNA maximally absorbs UV light.
What limited protection do cells have against the damaging effects of UV radiation? Cell protection against UV damage include the repair mechanisms, such as the SOS system, which enzymatically removes dimmers and inserts in their place new pyrimidine molecules.
What types of damage to human tissues can result from prolonged exposures to UV radiation? UV radiation can cause damage to skin cells and can cause skin cancers. It also can cause cataracts and eye injury.
What protective measures can be taken to limit these types of damage, both during the experiment as well as in everyday life? In this experiment, goggles are worn to protect the eyes and one should avoid looking directly at the UV light source. In everyday life, wearing long clothing, a hat, and/or sunscreen will protect against the damaging UV rays of the sun.
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Which B. megaterium culture, logarithmic or stationary phase, would show the best survival following exposure to UV radiation? Explain. A B. megaterium culture in stationary phase will contain more endospores as nutrients become limited and therefore would demonstrate the best survival following exposure to UV radiation.
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 Ultraviolet (UV) Lightnonionizing short wavelength radiation that falls between 4 nm and 400 nm in the visible spectrum.
 In general, for electromagnetic radiation, the ___ the wavelength, the more ___ it is to cells. shorter, damaging.
 UV light is much more ____ than either visible light or infrared radiation. Germicidal.
 Most bacteria are killed by the effects of ___ ___. Ultraviolet light.
 ____ ___ is routinely used to sterilize surfaces, such as the work areas of transfer hoods used for the inoculation of cultures. Ultraviolet light.
 The primary lethal effects of ultraviolet light are due to its ___ properties. mutagenic
 UV radiation at ___ is the most germicidal, and why is this the case? 260 nm, because this wavelength is the specific wavelength at which DNA maximally absorbs UV light.
 When DNA absorbs UV light, it causes the formation of ___. pyrimidine dimers.
 Pyrimidine dimersThese form when a covalent bond is formed between 2 adjacent thymine or cytosine molecules in a DNA strand.
 What do dimers essentially cause? It causes the DNA molecule to become deformed so that the DNA polymerase cannot replicate DNA strands past the site of dimer formation, nor can genes past this point be transcribed.
 Cells have evolved various ___ ___ to deal with mutational changes in DNA in order to insure that fidelity of replication occurs. repair mechanisms.
 SOS systema system which systematically removes the dimers and inserts in their place new pyrimidine molecules.
 Unlike ___ ____, enzymes of the ____ ___ can move beyond the point where dimers occur in the molecule. DNA polymerase, SOS system.
 However, if the exposure of UV light is sufficient to cause massive numbers of dimers to form in the DNA of a cell, why can't the SOS system cope with this situation? The SOS system is unable to effectively cope with this situation because it beings to make errors by inserting incorrect bases for the damaged bases, eventually resulting in cell death.
 The killing properties of UV light depend on several factors: Time of exposure, presence of materials that will block the radiation from reaching cells (ex. plastic), endospores
 What is an example of a material that would block radiation from reaching cells? Plastic can block UV radiation and plastic lenses are an effective means to protect the eyes from UV damage.
 What are 2 reasons why endospores more resistant to UV light than are vegetative cells? 1) The DNA of endospores is protected by small, acid-soluble proteins that bind to DNA and alter its conformation, thereby protecting it from photochemical damage.

2) A unique spore photo-product is generated by UV light in endospores that functions in enzymatic repair of damaged DNA during endospore germination.
 Which bacterium is an endospore former used to examine the germicidal effects for UV light? Bacillus megaterium.
 Which bacterium is an non-endospore former used to examine the germicidal effects for UV light? Staphylococcus aureus.
 What is the objective of this experiment? To examine the germicidal effects for UV light and to compare the relative resistance of vegetative cells and endospores.
 Why was half of each plate covered with an index card?The index card blocks the UV rays and provides direct comparison to the side that is exposed.
 What was the purpose of leaving the cover on one set of petri dishes?The ability of plastic, even clear, to block UV rays is demonstrated.
 Describe the damaging effects of UV radiation on living cells.UV radiation causes the formation of thymine dimmers in DNA that result in replication errors during reproduction. These error cause gene defects, which ultimately lead to cell death.
 Why does exposure to UV radiation cause death in vegetative cells but not endospores? Endospores are non-dividing cells and are not subject to the same effects as reproducing vegetative cells.
 At which wavelength is UV radiation most germicidal? Explain.UV radiation is most germicidal at 260 nm because that is the wavelength at which DNA maximally absorbs UV light.
 What limited protection do cells have against the damaging effects of UV radiation?Cell protection against UV damage include the repair mechanisms, such as the SOS system, which enzymatically removes dimmers and inserts in their place new pyrimidine molecules.
 What types of damage to human tissues can result from prolonged exposures to UV radiation? UV radiation can cause damage to skin cells and can cause skin cancers. It also can cause cataracts and eye injury.
 What protective measures can be taken to limit these types of damage, both during the experiment as well as in everyday life?In this experiment, goggles are worn to protect the eyes and one should avoid looking directly at the UV light source. In everyday life, wearing long clothing, a hat, and/or sunscreen will protect against the damaging UV rays of the sun.
 Which B. megaterium culture, logarithmic or stationary phase, would show the best survival following exposure to UV radiation? Explain. A B. megaterium culture in stationary phase will contain more endospores as nutrients become limited and therefore would demonstrate the best survival following exposure to UV radiation.
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