A 1-mL sample of the bacterium E. coli is exposed to ult...

Question

A 1-mL sample of the bacterium E. coli is exposed to ultraviolet light. The sample is used to inoculate a 500-mL flask of complete medium that allows growth of all bacterial cells. The 500-mL culture is grown on the benchtop, and two equal-size samples are removed and plated on identical complete-medium growth plates. Plate 1 is immediately wrapped in a dark cloth, but plate 2 is not covered. Both plates are left at room temperature for 36 hours and then examined. Plate 2 is seen to contain many more growing colonies than plate 1. Thinking about DNA repair processes, how do you explain this observation?

Accepted Answer

Hi, everybody. Let's look at our next question. It says which of the following enzymes in roopa binds to thymine. Diers produced by U V irradiation and uses visible light energy to break the bonds forming the dimer A DNA polymerase B DNA methyl transferase C DNA ligase or D photo lia. So we're talking about finding diers that get produced by U V radiation. So damage to DNA and we can recall that these thymine diers are an issue. It's caused when U V light causes the formation of a covalent bond between neighboring thin means. So instead of having the usual binding of an A and T residue, as part of our double helix, we form a new covalent bond between neighboring thymine. So if a thymine an extra thymine, thymine, U V light can cause this to happen. And why is that an issue? Because it can cause the two thymine can be replicated as a single base. So instead of being recognized as two T S, it's recognized as one T in DNA replication. And of course, if you delete a base, which would essentially be the effect of that, that will end up giving you a possible frame shift mutation, which can of course, be quite disastrous. So, these thymine diers are a problem. And so the cell has a mechanism to deal with them. And that is in the form of an enzyme that binds to these diam and uses our question, tells us visible light energy to break the dimer bond. Well, if we don't remember right away what that is, we've got a clue in that we're talking about an enzyme that uses light energy. And in choice D our enzyme name has the word photo in it. And indeed choice D photo Lia is our correct answer. We also have a clue in the second part of the name. A li ace. You think of lice, you think of breaking things. So photo Lia uses light to break a bond so that can help us get to that answer even if we don't remember it right away. Let's just look at our other answer. Choices. DNA polymerase is involved in the error proofing mechanisms, but as a proof reading enzyme and it can be used to detect and correct errors, but not specifically these dealing with these timing diers. So that's why that's not a correct answer. A DNA methyl transfer, as we can probably guess from the name methylate DNA transfers methyl groups to specific bases. So that's not our answer. And then finally DNA liga used to join DNA molecules together. So not what we're looking for. So again, the enzyme that uses visible light energy to break the bonds forming thymine diers that are produced by U V I radiation is choice D photo Lia. See you in the next video.

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