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Video instructions and help with filling out and completing Why Form 8815 Restrictions

Instructions and Help about Why Form 8815 Restrictions

When scientists began studying the way that bacterial cells protect themselves from different types of viral agents from bacteria phages they realize that inside bacterial cells are these special digestive proteins these special digestive enzymes known as restriction enzymes or restriction and the nucleases and what these restriction enzymes do is they are able to actually cut or cleave the viral DNA molecule into many different pieces thereby destroying that viral DNA and deactivating that viral DNA so one way that bacterial cells protect themselves from bacteria phages is by using these special enzymes we call restriction enzymes now because there are many different possibilities that a DNA sequence can consist of we have many many different types of restriction enzymes that exist in nature and each and every one of these restriction enzymes basically cleaves along a DNA molecule at a specific location on that double-stranded DNA molecule now many of these enzymes in our study of these restriction enzymes we realized that many of these restriction enzymes actually cut at palindromic sequences along that double-stranded DNA molecule and to see what we mean by a palindromic sequence of DNA let's take a look at the following diagram so let's suppose we have a we have a section a palindromic section of our double-stranded DNA so remember and any double stranded DNA molecule we have two single strands that run anti parallel with respect to one another so this blue strand begins at the 5 end and ends of the 3 end and this green strand begins at the 3 end and ends at the 5 and that's what we mean by anti parallel now we also have the base pairing between the two single strands and that's what holds the two strands together so we have the adenine children red we have the thymine shown in dark purple we have the orange that's the guanine we have the cytosine that's the light purple and so what we mean by palindromic sequences of DNA if we read these bases going this way we get the same exact reading if we go backwards so going this way along the blue single strand we have a a G C T T and going this way in the opposite direction along the green strand the other single strand we also get a a G C T T so that's exactly what we mean by a palindromic sequence and most of these restriction enzymes restriction enzymes basically look for these types of palindromic sequences on the DNA and that's where they cleave those DNA molecules so for this particular example let's suppose we add some sort of restriction enzymes that looks for this specific palindromic sequence what the enzyme does is it finds that palindromic sequence and it cuts at a specific location along that DNA molecule so for example let's say this restriction enzyme that we add cuts between the a bases between the adenine bases along this specific palindromic sequence so that means because we have two a's here and two AAS here we have the restriction enzyme cuts not only here but it also cuts here and once we cut those single strand molecules these hydrogen bonds basically dissociate and we form the following molecule so now we basically have this asymmetric uneven cut and the reason we have an asymmetric cut is now we have these single strands of DNA molecule are exposed so they're no longer connected but they are exposed so here we still have a double helix and here we still have a double helix but within this section and within this section we have single strands that are exposed and these single strands are commonly known as sticky ends why do we call them sticky ends well because they are complementary with respect to one another and if we somehow allow them to reconnect and then we use a special type of enzyme to reform these bonds right over here these sticky ends because they're complementary they're going to stick right back together now when science has discovered this they realize that one important application of restriction enzymes will be to form recombinant DNA molecules so remember a recombinant DNA molecule is a DNA molecule that consists of two or more different DNA sequences DNA molecules so to see what we mean by that let's take a look at the following diagram so let's suppose we have two different DNA molecules so DNA molecule number one and DNA molecule number two that basically came from two different sources and what we want to do is we want to somehow combine these two DNA molecules and to form a single recombinant DNA molecule that consists of these two different DNA molecules so the way that we do it is we basically realize that let's say these two different DNA molecules both contain these palindromic sequences that we discussed earlier so let's say this is the palindromic sequence on this molecule that reflects this and this is the palindromic sequence on the second DNA molecule that also reflects this sequence here so we have the red the red the orange the light purple dark purple dark purple that reflects this and then along the green section we have the purple the purple the light purple that orange red and red and the same type of palindromic sequence is found on this second DNA molecule as well so we have red red orange light purple dark purple dark purple on one strand and the lower strand has the dark purple dark purple light purple orange red and red so let's suppose we take these two DNA molecules and now we add the same restriction enzyme that we basically used in this particular case and what that means is this restriction enzyme will move along the DNA molecule until it locates this specific palindromic sequence and once it locates that palindromic sequence it will clean between the bases.

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