Gel Electrophoresis - Free Educational videos for Students in K-12

Gel Electrophoresis - By MITK12Videos

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00:09	Have you ever wondered how the police identified the culprit
00:12	of a theft when he doesn't leave behind any fingerprints
00:15	, but often leaves behind something as simple as a
00:17	strand of hair ? For example , imagine that the
00:21	moment lisa has been stolen and the police have arrested
00:24	several suspects . They have also found a strand of
00:26	hair left behind at the crime scene . How can
00:29	the police use the DNA in the follicle of the
00:31	hair to identify the thief ? Well , since no
00:35	two people have the same DNA , the hair DNA
00:37	can be used to definitively figure out who took the
00:40	painting by using DNA fingerprinting through a process known as
00:43	gel electrophoresis , gel electrophoresis is the separation of DNA
00:49	fragments by size . Today we will use gel electrophoresis
00:53	to match the DNA fragments in the hair to the
00:55	DNA of the suspects . Here we have a gel
00:58	and the gel box . The gel has a row
01:00	of wells on one end where we will put the
01:02	DNA samples . But how does the DNA separate ?
01:05	As we all learned ? When we were younger ,
01:07	opposite charges are attracted to each other . Using this
01:10	principle DNA , which is negatively charged due to the
01:13	negative phosphate groups in the backbone , will be attracted
01:15	towards the positive end of the box when the current
01:17	runs through it . When the current is running ,
01:21	the DNA will separate through the gel with the smaller
01:24	fragments moving faster than the larger ones and thus moving
01:27	further down the gel . But why ? Let's imagine
01:30	that the gel , which is made up of long
01:32	intertwined chains of proteins called polymers , is like a
01:35	forest with tall trees spaced apart from each other .
01:39	You are carrying a 2-foot pole and your friend is
01:41	carrying a 10-foot pole . And you both want to
01:43	carry your respective polls from one under the forest to
01:46	the other . As you can probably guess , you
01:49	will reach the other end faster than your friend because
01:51	it's easier to maneuver the smaller two ft pull through
01:54	the forest than the larger 10 ft pole . In
01:56	the same way , it's easier for a smaller DNA
01:58	fragment to maneuver through the gel than a larger DNA
02:01	fragment . If we want to look at a diagram
02:04	, it would look something like this . The Y
02:06	axis is speed a movement through the gel and the
02:09	X . Axis is DNA fragment size . As you
02:11	can see , there's an inverse relationship between the two
02:15	. One end shows that the smallest DNA fragment size
02:17	moves the fastest while the other end shows that larger
02:20	DNA fragments move slower . Before we load the samples
02:25	into the wells of the gel , we need to
02:27	load a ladder in the first plane . The latter
02:29	is , and make sure of different DNA fragments uses
02:31	a standard of reference to determine the sizes of unknown
02:34	fragments . The unit of measurement used to refer to
02:37	the size of DNA is known as a base pair
02:39	, or B . P . For short . Now
02:42	we can take the DNA from the three suspects mix
02:45	each of them with a dye and load them into
02:47	the wells next to the latter . Here is a
02:50	closer look at how the gel is being loaded .
02:56	Once we turn on the current , the DNA will
02:58	start moving through the gel towards the positive end ,
03:01	as we have explained earlier . Now , we have
03:04	our samples running on the gel . This process usually
03:07	takes about an hour , but we have sped it
03:08	up here . The individual bands of DNA cannot be
03:11	seen when running the gel but can be visualized under
03:14	UV light afterwards . To make sure the DNA does
03:17	not run off the gel . We monitor the loading
03:19	die shown in blue , which runs ahead of the
03:21	DNA and can be seen with the naked eye .
03:24	Here is an illustration of how the DNA moves when
03:26	the gels running . If we could actually see what
03:29	was going on , as you can see all the
03:31	DNA bands of different sizes start out , clump together
03:33	at the wells and then slowly separate based on size
03:36	. Over time . Now that our gel has finished
03:40	running , we can visualize the bands in a gel
03:43	imager using UV light . The gel imager is connected
03:46	to a camera that then takes a picture of the
03:48	gel with the DNA bands visible . These are examples
03:53	of what gels visualized under UV light with a gel
03:56	imager looked like . Here's our finished gel picture as
04:01	you can see . And call them one . We
04:02	have the ladder Column two has suspect , 1's DNA
04:06	. Column three has suspect too in common four has
04:09	suspect threes . The last column has the mystery DNA
04:13	. From the hair strand found at the crime scene
04:15	. As we mentioned earlier , Each person has a
04:18	unique set of DNA . So the DNA location on
04:21	the gel or in other words , the DNA sizes
04:25	should match between the suspect who actually committed the crime
04:28	and the hair is DNA . In our case ,
04:32	that's suspect too . Each DNA band in the mystery
04:36	DNA column appears in the same location in suspects .
04:39	To column indicating that the two DNA samples come from
04:42	the same person . What else can we tell from
04:45	the jail results ? Well , remember how we said
04:48	earlier that the latter can be used to figure out
04:50	the size of an unknown fragment of DNA . Let's
04:53	try to do just that with suspect two's DNA .
04:56	The first fragment is at the very top of the
04:58	gel and lines up with the 1000 base pair ladder
05:01	marker . So we know that that fragment is around
05:03	1000 base pairs long . The second fragment is trickier
05:07	because it doesn't line up perfectly with the latter marker
05:09	. So we need to estimate the size Since it's
05:12	between the 500 and 800 base pair markers . But
05:15	closer to the 501 will say that is approximately 550
05:19	base pairs . In the same way we can determine
05:22	that the size of the last fragment is approximately 225
05:25	base pairs . Law . In summary , we learned
05:29	that DNA can be separated based on size using gel
05:32	electrophoresis and the results are applicable to real world scenarios
05:36	such as DNA fingerprinting to solve crimes . Mhm mm
05:50	. Yeah . Mm . Yeah . Mm .

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