carly
New Member
Posts: 9
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Post by carly on Apr 29, 2012 17:03:31 GMT -5
yes scan thank you! Also were you mentioning something about first year calc. notes? That would be awesome.
Yes. I already scanned those this morning. They are posted under the notes section--subsection Math Notes.
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Post by amanda on May 3, 2012 12:49:21 GMT -5
Ms that would be amazing if you could scan your notes ur teaching style is amazing and it would really be a lot of help if we had them just in case we don't understand something thank you so much Ms your amazing Already done. They are under the notes section as powerpoints (each of the scanned pages is a file). I have my homeostasis ones, pop dynamics and first year calc. I hope they help
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Post by Brittany on May 4, 2012 16:28:32 GMT -5
Will any of the previous multiple choice questions from our last two tests be on the upcoming test?
Not exactly. I made all new questions. So none of the questions will be the exact same though you may find ones that are quite similar.
Also, this is my last reply. Any questions anyone has over the weekend will be answered by my friend, Samantha. Good luck everyone!
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seema
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Post by seema on May 5, 2012 22:18:59 GMT -5
Hello, I have a question about the enzyme Methylase It says that it adds methyl groups to the restriction site to prevent the restriction enzyme from cutting there. I don't understand this because isn't the point of the restriction site to act as a place for the restriction enzyme to cut? I know biologists purposely methylate sometimes, but when would methylase work on its own? What is its purpose
Hey, good question. So, although restriction sites are a place of enzymatic cleavage, not all cells want their restriction enzymes to cut all of their available restriction sites. For example, bacterial cells produce restriction enzymes to protect themselves from foreign DNA introduced by an infectious agent. The restriction enzymes cleave the foreign DNA and thus prevent the spread of infection. However, restriction enzymes are unable to distinguish between foreign DNA and host DNA and it is almost certain that the host DNA will have the same restriction site sequences as the foreign DNA. So, in order to prevent the destruction of its own DNA by its own restriction enzymes, the bacterium marks its own DNA by adding methyl groups to it. That's just one example of how methylase works on its own. But hey, don't worry too much about this because from what I've seen that won't be on your test!
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carly
New Member
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Post by carly on May 6, 2012 11:13:20 GMT -5
Hi, quick question about the PCR. In our notes it sats that in the second cycle, two of the strands run from target region to target region? And that the other two strands behave the same way as cycle one. Why is this? If it started with two strands (cycle 1) and became four during the second cycle, what differentiates the two that run target to target and the other two that behave as cycle one, what happened to make them different? Thanks!
Hey, so remember when the second cycle starts, there are two types of DNA templates: Type 1) the original DNA strands which extend past the target region on both sides Type 2) the newly synthesized DNA strands which, because of the primer, begin at one end of the target region and only extend past one side
Now when the second cycle begins, and the DNA is split into 4 single strands, the two types of DNA templates will vary in their replication.
The original strands (type 1) will act like they did in the first cycle in that the primer will bind to one end of the target region and DNA synthesis will proceed through the region and past it for a variable distance ("variable length strands"), just like in cycle one.
However, the newly synthesized DNA strands (type 2) only begin at one end of the target region, so after they are denatured, the primer will bind to them on the opposite end of the target region and DNA synthesis will proceed through the region but cannot extend past it because that is where the DNA fragment ends. So that is why these strands can only run from target to target.
Does this make sense? Sometimes I confuse even myself, but hopefully this helps!
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carly
New Member
Posts: 9
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Post by carly on May 6, 2012 15:29:46 GMT -5
That makes so much more sense now thanks! So will you always have a few in each cycle of replication that replicate without going target to target, since the original two strands will continue to replicate?
You're right! But, since the amount of DNA increases exponentially every cycle, the amount of those strands becomes negligent to the amount of the actual target strands.
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Post by Brittany on May 6, 2012 15:34:19 GMT -5
Hi, I know that we have to be able to read a gel, but I don't understand what that is/how to do that. I know that a gel can be used in fingerprinting and separates dna fragments base on size, but how do you read a gel? Thanks! Basically, you have a sample of DNA you want to analyze so you cleave it into fragments using restriction endonuclease digestion and treat it with Ethidium Bromide to make it visible later. Now you get your gel ready by placing it in a buffer to allow an electric current to travel through it. You need a current to allow the DNA to move through the gel. This is because DNA holds a negative charge due to its possession of a phosphate group. So, if you place the DNA sample into the wells at the negative end of the gel, once you hook it up to electrodes, the charge travels through the buffer and the negatively charged DNA will move down through the gel towards the positive end. Okay, so you’ll end up noticing that the fragments of DNA move at different speeds through the gel. This is because the gel consists of number pores which the DNA fragments have to navigate through in order to reach the positive end. The lengths of the DNA fragments determine how fast they can move through these pores. If the fragment is longer, it moves slower through the gel and if the fragment is shorter, it moves faster. Think of it this way, if there was a dense crowd of people blocking an exit, a small child would more easily be able to thread a path through the crowd because of their small size compared to a football player who would have a more difficult time navigating through the crowd due to their large size. So the small child would get to the exit sooner and the football player would get their later, just like a small fragments would make their way through the gel quicker and larger fragments would make their way more slowly.
Once the gel electrophoresis is complete, the DNA fragments are made visible by staining the gel and placing under UV light. The set of fragments produce a noticeable banding pattern characteristic for that DNA, this is the gel reading. The banding pattern looks like a bunch of different lines in a column. Well, each of these lines represents a fragment of DNA. Now these fragments are a number of different lengths, but they look about the same size in the picture because DNA is so small that actual difference in length between the fragments is microscopic. The way you know the difference in length is by looking at where the fragment is located. The top of the column represents the top of the gel (the negative end) the bottom of the column represents the bottom of the gel (the positive end). Thus, the fragments located at the top of the column are the ones that took the most time to move through the gel. Meaning they are the longest fragments. And the fragments at the bottom of the column are the ones that moved the quickest through the gel. Meaning they are the shortest fragments.
Also, when you are comparing banding patterns from different DNA samples, if the DNA is similar or from the same person, the pattern will be similar or almost exactly the same. Like in paternity testing, if you compare the banding pattern of the mother and father to that of the baby, you will find that the baby’s banding pattern is a combination of the two parents, so it will look similar to both of them. And if you were trying to link the DNA of a suspect to the DNA found at a crime scene, the banding pattern for both of the DNA samples would have to be almost the same.
Therefore, if you were reading a gel, understand that the longest fragments are the lines on top and the shortest fragments are the lines on the bottom. And that similar gel patterns indicate a relationship between the DNA of the people being compared.
Sorry, this is such a long explanation (and for the late response!). If any of this is unclear let me know and I’ll try to be clearer in my answer!
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Post by lauren on May 6, 2012 21:23:32 GMT -5
Hi I am really confused at what steps we have to do when we are trying to map plasmids. I don't know which part of the chart to start off with.
Hey, I am soo sorry this is posted so late. Mapping plasmids is weirdly difficult so I posted the steps I used to do it in the post below and hopefully that answers some of your questions! I hope you see this in time and good luck on your test!
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Post by amanda on May 6, 2012 21:40:33 GMT -5
wow thanks your answer on how to read a gel was perfect and clarified everything in one answer thank you so much and yes i am also still confused about mapping plasmids You're welcome, I'm glad it helped! And for mapping plasmids, look at the post below and hopefully that clears some stuff.
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Post by Miss DiFederico on May 7, 2012 1:36:58 GMT -5
Hey guys, this is this really late so sorry if you don't see this in time, but I understand that a lot of you have been having problems with mapping plasmids. Well, I haven't done this in a while, but I used an example question given to me by one of you guys and wrote out the steps I would use to solve it. I've posted the steps as an attachment. I think that these steps might different from Miss Difederico's steps, so if you understand her way than stick with it. If you understand my way, than I hope this helps. Once again, I'm really sorry this is posted so late, I didn't see all of your questions until just recently (I forgot to check, my bad!). But I obviously stay up at all hours so if you guys still have questions I'm still here to answer them for now and I promise to do it promptly!Attachments:
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