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Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:03.68,Default,,0000,0000,0000,,Captioning is on. Click the CC button at bottom right to turn off.
Dialogue: 0,0:00:03.68,0:00:08.30,Default,,0000,0000,0000,,Follow us on Twitter (@amoebasisters) and Facebook!
Dialogue: 0,0:00:08.34,0:00:14.00,Default,,0000,0000,0000,,DNA. We talk about it so much---it is the\Nultimate director for cells and it codes for
Dialogue: 0,0:00:14.00,0:00:19.93,Default,,0000,0000,0000,,your traits. It’s a major component of what\Nmakes you, you. When you have a really important
Dialogue: 0,0:00:19.93,0:00:25.19,Default,,0000,0000,0000,,molecule like DNA that is ultimately responsible\Nfor controlling the cell…it would make sense
Dialogue: 0,0:00:25.19,0:00:32.19,Default,,0000,0000,0000,,that when you make another cell (like in mitosis),\Nyou would also have to get more DNA into that
Dialogue: 0,0:00:32.50,0:00:39.46,Default,,0000,0000,0000,,cell. And that introduces our topic of DNA\Nreplication, which means, making more DNA.
Dialogue: 0,0:00:39.46,0:00:46.46,Default,,0000,0000,0000,,First let’s talk about where and when.First\Nwhere---it occurs in the nucleus. If the cell
Dialogue: 0,0:00:48.08,0:00:54.07,Default,,0000,0000,0000,,has a nucleus. Remember, not all cells have\Na nucleus. This video clip is actually going
Dialogue: 0,0:00:54.07,0:01:00.97,Default,,0000,0000,0000,,to focus on the types of cells that do have\Na nucleus though known as eukaryote cells.
Dialogue: 0,0:01:00.97,0:01:07.97,Default,,0000,0000,0000,,Prokaryotes, which are cells that lack a nucleus,\Ndo things a little differently. Next When
Dialogue: 0,0:01:13.82,0:01:19.86,Default,,0000,0000,0000,,does this happen---this typically happens\Nduring a stage known as interphase. Interphase
Dialogue: 0,0:01:19.86,0:01:25.12,Default,,0000,0000,0000,,is when a cell’s growing, it’s carrying\Nout cell processes, and it’s replicating
Dialogue: 0,0:01:25.12,0:01:31.12,Default,,0000,0000,0000,,its DNA. You know what it’s not doing at\Nthe exact same time? Dividing. You don’t
Dialogue: 0,0:01:31.12,0:01:36.03,Default,,0000,0000,0000,,want a cell to be replicating DNA and dividing\Nat the exact same time. That’s a little
Dialogue: 0,0:01:36.03,0:01:43.02,Default,,0000,0000,0000,,bit too much multitasking. So DNA replication\Ndoes not happen during cell division (aka
Dialogue: 0,0:01:43.02,0:01:50.02,Default,,0000,0000,0000,,mitosis). In fact, the cell replicates its\NDNA before division processes like mitosis
Dialogue: 0,0:01:50.10,0:01:56.09,Default,,0000,0000,0000,,and meiosis. Because once you make that new\Ncell, you better have DNA to put in there.
Dialogue: 0,0:01:56.09,0:02:01.40,Default,,0000,0000,0000,,I think DNA replication would actually make\Na great video game. It’s actually quite
Dialogue: 0,0:02:01.40,0:02:05.94,Default,,0000,0000,0000,,exciting. I’m going to introduce the key\Nplayers in DNA replication so that you can
Dialogue: 0,0:02:05.94,0:02:11.81,Default,,0000,0000,0000,,get some background information. The majority\Nof these key players that I’m going to introduce
Dialogue: 0,0:02:11.81,0:02:18.32,Default,,0000,0000,0000,,are enzymes. In biology, when you see something\Nend in –ase, you might want to check as
Dialogue: 0,0:02:18.32,0:02:24.06,Default,,0000,0000,0000,,it is very possible that it’s an enzyme.\NEnzymes have the ability to speed up reactions
Dialogue: 0,0:02:24.06,0:02:31.06,Default,,0000,0000,0000,,and build up or break down the items that\Nthey act on. So here we go with the key players.
Dialogue: 0,0:02:32.32,0:02:39.23,Default,,0000,0000,0000,,Helicase- the unzipping enzyme. If you recall\Nthat DNA has 2 strands, you can think of helicase
Dialogue: 0,0:02:39.23,0:02:44.09,Default,,0000,0000,0000,,unzipping the two strands of DNA. Helicase\Ndoesn’t have a hard time doing that. The
Dialogue: 0,0:02:44.09,0:02:46.37,Default,,0000,0000,0000,,hydrogen bonds that hold the DNA strands together\Nis pretty weak compared to other kinds of
Dialogue: 0,0:02:46.37,0:02:49.88,Default,,0000,0000,0000,,bonds. DNA Polymerase- the builder. This enzyme\Nreplicates DNA molecules to actually build
Dialogue: 0,0:02:49.88,0:02:56.88,Default,,0000,0000,0000,,a new strand of DNA. Primase- The initializer.\NWith as great as DNA polymerase is, poor DNA
Dialogue: 0,0:02:57.38,0:03:02.51,Default,,0000,0000,0000,,polymerase can’t figure out where to get\Nstarted without something called a primer.
Dialogue: 0,0:03:02.51,0:03:07.03,Default,,0000,0000,0000,,Primase makes the primer so that DNA polymerase\Ncan figure out where to go to start to work.
Dialogue: 0,0:03:07.03,0:03:12.36,Default,,0000,0000,0000,,You know what’s kind of interesting about\Nthe primer it makes? It’s actually a piece
Dialogue: 0,0:03:12.36,0:03:19.36,Default,,0000,0000,0000,,of RNA. Ligase- the gluer. It helps glue DNA\Nfragments together. More about why you would
Dialogue: 0,0:03:20.71,0:03:26.83,Default,,0000,0000,0000,,need that later. Don’t feel overwhelmed.\NWe’ll go over the sequence in order. Please
Dialogue: 0,0:03:26.83,0:03:32.10,Default,,0000,0000,0000,,keep in mind, that like all of our videos,\Nwe tend to give the big picture but there
Dialogue: 0,0:03:32.10,0:03:38.41,Default,,0000,0000,0000,,are always more details to every biological\Nprocess. There is more involved than what
Dialogue: 0,0:03:38.41,0:03:44.32,Default,,0000,0000,0000,,we cover. DNA replication starts at a certain\Npart called the origin. Usually this part
Dialogue: 0,0:03:44.32,0:03:50.31,Default,,0000,0000,0000,,is identified by certain DNA sequences. There\Ncan be multiple origins within the DNA strand.
Dialogue: 0,0:03:50.31,0:03:57.31,Default,,0000,0000,0000,,At the origin, helicase (the unzipping enzyme)\Ncomes in and unwinds the DNA.
Dialogue: 0,0:03:57.42,0:04:05.16,Default,,0000,0000,0000,,SSB proteins (which stands for single stranded binding\Nproteins) bind to the DNA strands to keep
Dialogue: 0,0:04:05.17,0:04:11.79,Default,,0000,0000,0000,,them separated. Primase comes in and makes\NRNA primers on both strands. This is really
Dialogue: 0,0:04:11.79,0:04:17.29,Default,,0000,0000,0000,,important because otherwise DNA polymerase\Nwon’t know where to start.
Dialogue: 0,0:04:17.40,0:04:24.78,Default,,0000,0000,0000,,Now comes DNA Polymerase. Remember, it’s the important enzyme that adds DNA bases.
Dialogue: 0,0:04:24.79,0:04:30.18,Default,,0000,0000,0000,,Now you have 2 strands right? But they’re not identical.Remember they complement each other. They
Dialogue: 0,0:04:30.18,0:04:37.18,Default,,0000,0000,0000,,also are anti-parallel so they don’t really\Ngo in the same direction.
Dialogue: 0,0:04:37.18,0:04:44.10,Default,,0000,0000,0000,,With DNA, we don't say it goes North or South. The directions for the DNA strands are a little different.
Dialogue: 0,0:04:44.11,0:04:51.11,Default,,0000,0000,0000,,We say that DNA either goes 5’ to 3’ or\N3’ to 5’. What in the world does that
Dialogue: 0,0:04:51.34,0:05:01.00,Default,,0000,0000,0000,,mean? Well the sugar of DNA is part of the\Nbackbone of DNA. It has carbons. The carbons
Dialogue: 0,0:05:01.00,0:05:08.00,Default,,0000,0000,0000,,on the sugar are numbered right after the\Noxygen in a clockwise direction. 1’, 2’
Dialogue: 0,0:05:08.18,0:05:17.02,Default,,0000,0000,0000,,3’, 4’ and 5.’ The 5’ carbon is actually\Noutside of this ring structure. Now you do
Dialogue: 0,0:05:17.22,0:05:24.38,Default,,0000,0000,0000,,the same thing for the other side but keep\Nin mind this strand is flipped just because
Dialogue: 0,0:05:24.38,0:05:30.27,Default,,0000,0000,0000,,DNA strands are anti-parallel to each other.\NSo let’s count these---again, clockwise
Dialogue: 0,0:05:30.27,0:05:37.27,Default,,0000,0000,0000,,after the oxygen. 1’, 2’ 3’, 4’ 5’.\NAnd the 5’ is out of this ring. This strand
Dialogue: 0,0:05:37.34,0:05:46.38,Default,,0000,0000,0000,,on the left runs 5’ to 3’ and the strand\Non the right here runs 3’ to 5’. Well,
Dialogue: 0,0:05:48.95,0:05:55.04,Default,,0000,0000,0000,,it turns out that DNA polymerase can only\Nworks in the 5’ to 3’ direction. So…the
Dialogue: 0,0:05:55.04,0:06:02.00,Default,,0000,0000,0000,,strand that runs 5’ to 3’ is fine. It\Nis called the leading strand. But the other
Dialogue: 0,0:06:02.00,0:06:07.73,Default,,0000,0000,0000,,strand will make it a little tricky. DNA polymerase\Ncan only go in the 5’ to 3’ direction.
Dialogue: 0,0:06:07.73,0:06:13.72,Default,,0000,0000,0000,,(NOTE: Reads in 3' to 5' direction). Primase has to set a lot of extra primers down to
Dialogue: 0,0:06:13.72,0:06:20.72,Default,,0000,0000,0000,,do that as shown here. It takes longer too.\NThis strand is called the lagging strand which
Dialogue: 0,0:06:21.40,0:06:27.16,Default,,0000,0000,0000,,is pretty fitting.On the lagging strand, you\Ntend to get little fragments of synthesized
Dialogue: 0,0:06:27.16,0:06:33.02,Default,,0000,0000,0000,,DNA. These are called Okazaki fragments. Okazaki.\NWhat an amazing name. The primers have to
Dialogue: 0,0:06:33.02,0:06:40.02,Default,,0000,0000,0000,,get replaced with DNA bases since the primers\Nwere made of RNA. Ligase, the gluing enzyme
Dialogue: 0,0:06:40.62,0:06:46.16,Default,,0000,0000,0000,,as I like to nickname it, has to take care\Nof the gaps in the Okazaki fragments.Now at
Dialogue: 0,0:06:46.16,0:06:52.02,Default,,0000,0000,0000,,the end, you have two identical double helix\NDNA molecules from your one original double
Dialogue: 0,0:06:52.02,0:06:59.02,Default,,0000,0000,0000,,helix DNA molecule. We call it semi-conservative\Nbecause the two copies each contain one old
Dialogue: 0,0:07:01.05,0:07:08.05,Default,,0000,0000,0000,,original strand and one newly made one. One\Nlast thing. Surely you have had to proofread
Dialogue: 0,0:07:08.83,0:07:14.05,Default,,0000,0000,0000,,your work before to catch errors? Well, you\Ndefinitely don’t want DNA polymerase to
Dialogue: 0,0:07:14.05,0:07:21.05,Default,,0000,0000,0000,,make errors. If it matches the wrong DNA bases,\Nthen you could have an incorrectly coded gene…which
Dialogue: 0,0:07:21.11,0:07:28.10,Default,,0000,0000,0000,,could ultimately end up in an incorrect protein---or\Nno protein. DNA polymerase is just awesome…it
Dialogue: 0,0:07:28.10,0:07:35.10,Default,,0000,0000,0000,,has proofreading ability. Meaning, it so rarely\Nmakes a mistake. Which is very good. That’s
Dialogue: 0,0:07:35.55,0:07:38.41,Default,,0000,0000,0000,,it for the amoeba sisters and we remind you\Nto stay curious!
Dialogue: 0,0:07:38.41,0:07:47.57,Default,,0000,0000,0000,,Follow us on Twitter (@amoebasisters) and Facebook!