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Fluorescent Probes: Organic Dyes and Quantum Dots

00:00:11.14 My name is Tim Mitchison, I'm from Harvard Medical School
00:00:14.22 I've been working with fluorescent probes
00:00:17.08 since before we had fluorescent proteins
00:00:19.13 or at least before they were widely used
00:00:21.20 and I've done quite a bit of chemistry and that kind of thing myself
00:00:26.14 and I really love these molecules
00:00:28.05 one of the things I would like to give you guys
00:00:30.22 is some appreciation for this beautiful molecules
00:00:33.22 and their properties and particularly how their chemistry
00:00:37.16 gives rise to their properties
00:00:39.26 for those of you who aren't chemists
00:00:42.18 you know, don't worry I'm gonna try to make it
00:00:44.23 as easier as possible
00:00:47.06 ok, so the outline of this presentation
00:00:49.29 we're are gonna be talking about
00:00:51.09 probe chemistry and then we will talk about
00:00:54.10 protein labeling and then finally
00:00:56.20 non-covalent targeting of probes
00:00:59.05 ok, and in the chemistry section here
00:01:02.06 I wanna talk about the structure of probes
00:01:05.00 I wanna spend quite a bit of time on that
00:01:06.12 people buy a probe from a catalog
00:01:09.23 and they attach it to a protein
00:01:11.00 never really thinking about what
00:01:12.01 that molecule actually is
00:01:13.05 I would like to encourage you
00:01:14.09 and give some tips for really looking
00:01:16.08 and appreciating these molecules
00:01:17.29 talk about how the wavelength
00:01:19.18 is determined, just briefly mention
00:01:21.20 quantum dots and then issues like
00:01:24.07 photobleaching and photodamage
00:01:26.09 so we will start here
00:01:28.19 this is really, I want to sort of
00:01:30.19 how to look at probes' structure
00:01:32.03 I think a nice place to start
00:01:33.21 is this beautiful molecule here
00:01:35.29 fluorescein
00:01:36.27 arguably the first synthetic probe
00:01:39.03 synthesized in 1871 as part of the
00:01:42.19 German dye industry that was going on
00:01:45.08 at that time so people were building
00:01:47.13 dye molecules for commercial applications
00:01:50.00 and this is a sort of like a dye molecule
00:01:52.04 it's highly colored and fluorescein
00:01:54.25 is still in use today, it's for example
00:01:57.08 it's a very cheap, non-toxic, you can use it to trace
00:02:00.05 flow in underground rivers, and it's a molecule I've made myself
00:02:04.14 many of times. Is actually one of the most fun things
00:02:07.04 I've done in science, you take two white molecules
00:02:10.11 and you cook them up in a strong acid overnight
00:02:12.23 you come in the next day, and you've got this brilliantly
00:02:15.05 colored solution, and if you put a drop of it in water
00:02:17.26 the whole thing goes green fluorescent
00:02:20.19 so, it's a really very fun kind of molecule.
00:02:23.28 now, the fluorescent properties of fluorescein are pH dependent
00:02:27.08 this form over here, with the O minus is just the high pH form
00:02:33.22 is the fluorescent one, you can see here the excitation
00:02:36.14 and emission spectra
00:02:38.12 and so I'm really only be talking about
00:02:40.10 this one and its ability to switch between
00:02:42.08 fluorescent and non-fluorescent has many applications
00:02:47.06 this is I hope review, you should have heard about
00:02:50.20 Jablonski Diagrams in Nico's talk when he was talking
00:02:54.05 about the principles of fluorescence
00:02:55.16 here I really only want to focus on the HOMO
00:02:59.05 the highest occupied molecular orbital
00:03:01.22 and the LUMO the lowest unoccupied
00:03:03.22 and of course the energy difference between these
00:03:06.12 is what determines the color or the wavelength
00:03:08.20 of the fluoro, the smaller the energy difference
00:03:11.21 the redder the fluoro
00:03:14.14 and I want to relate that to the structures
00:03:16.21 so the part of the fluorescein molecule that really matters
00:03:19.19 for its fluorescence, this lower ring system doesn't matter
00:03:21.28 you can use that for attaching to proteins
00:03:25.16 it's this other part here that you can see extending
00:03:29.03 from this O minus up to this carbonyl here
00:03:33.05 and if you look there's alternating single and double bonds
00:03:35.19 here, which means it's a conjugated structure
00:03:38.09 in fact, the electrons can be in an orbital that expands
00:03:41.19 across this whole structure here
00:03:43.21 we call this an extended orbital, and it turns out
00:03:47.28 that the larger this extended orbital typically
00:03:50.27 the lower the difference between the HOMO and the LUMO
00:03:53.26 and the redder the fluoro
00:03:55.10 you will also notice almost all fluorochromes have
00:03:58.11 an electron donor, at this end O minus
00:04:01.12 and an electron acceptor, at this end the double bond O
00:04:05.17 so you've got a kind of a push-pull system
00:04:09.03 but this is a symmetric push-pull system
00:04:11.13 the two are essentially the same here
00:04:13.23 and this symmetric conjugated orbital it turns out
00:04:17.27 reduces quenching by other dipoles like water
00:04:22.05 you can also have fluorescent molecules with
00:04:23.27 a permanent donor at one end, like an amine
00:04:27.07 and a permanent acceptor at the other end, like a ketone
00:04:30.00 those can be very fluorescent inorganic ???
00:04:32.11 but they don't tend to fluoresce as well in water
00:04:34.10 and it turns out the symmetry here is also responsible
00:04:37.17 for the fairly small Stokes shift, the small difference
00:04:39.24 between the excitation and the absorption
00:04:42.29 and the one other notable point about this structure
00:04:45.02 if you look at this extended orbital here
00:04:47.00 there are no rotatable bonds
00:04:49.03 the whole thing is rigidly locked into this three rings
00:04:52.12 and it turns out if the molecule can rotate
00:04:54.27 it tends to be awake and lose energy
00:04:56.29 and become less fluorescent
00:04:59.26 now first let me talk a little bit more about the size issue
00:05:02.08 compare two molecules here
00:05:03.21 that I hope you can see whether you are a chemist or not
00:05:05.27 are really fairly similar
00:05:06.23 fluorescein, and here this is a coumarin derivative
00:05:09.16 and basically we've chopped out one of the rings
00:05:12.24 and getting from here to here
00:05:13.24 and if you look at the fluorescence
00:05:15.04 this is 488 excitation, 510 emission
00:05:19.11 this is considerably shorter and that's just because
00:05:22.05 the conjugated orbital is smaller
00:05:25.03 you can actually add another ring into fluorescein
00:05:27.25 you get something called a naphthoflourescein
00:05:29.20 and that will shift it out into the red
00:05:32.02 so size is one factor
00:05:33.16 another factor, the actual atoms matter though
00:05:36.17 here is two more similar molecules
00:05:38.13 fluorescein we've already talked about
00:05:39.25 this is another similar molecule
00:05:41.13 I call it "reso-rufin", I'm not sure if "resoru-fin" is more correct
00:05:45.14 but you can see in place of the carbon here in fluorescein
00:05:51.08 there's a nitrogen and it turns out that
00:05:53.15 shifts the wavelength considerably into the red
00:05:56.10 and I don't understand the kind of quantum mechanics
00:05:58.26 that goes on, but that's often the case with heteroatoms
00:06:03.15 so you've seen here two ways you can kind of tune the wavelength
00:06:06.07 by changing the size and the atoms
00:06:08.23 and then here is the point about rigidity
00:06:10.18 comparing fluorescein to another closely related molecule phenolphthalein
00:06:14.21 the only difference here is this bridgehead oxygen is missing
00:06:17.20 and that means you can rotate around this bond here
00:06:21.08 so these rings can twist
00:06:22.22 as a result phenolphthalein is highly colored and its high pH form it's purple
00:06:27.10 it's used as an indicator dye
00:06:29.04 but it's not at all fluorescent
00:06:31.03 basically the LUMO can lose energy very rapidly by a rotational process
00:06:37.02 so rigidity matters as well as size
00:06:40.07 and basically by tuning those kinds of properties
00:06:43.19 the size of the system
00:06:46.05 the heteroatoms
00:06:48.28 and keeping everything rigid
00:06:50.16 it's been possible for chemists to build a series of dyes
00:06:54.22 that cover the whole visible spectrum
00:06:58.19 all the way out here from the ultraviolet
00:07:03.03 into the point where water starts to absorb
00:07:06.11 so this is the usual useful spectrum we have in microscopy
00:07:09.15 this particular set here is the Alexa dyes
00:07:12.05 is made by Molecular Probes
00:07:13.06 I will show you some structures of those
00:07:14.26 but there are comparable dyes made by other people
00:07:19.13 one point I wanna make, you often see diagrams like this
00:07:21.28 these are the absorption spectra
00:07:25.08 and they've all been normalized
00:07:26.24 so they have the same height
00:07:28.19 in fact, the absorption coefficient, the efficiency of absorbing light
00:07:32.20 scales strongly with the size of the orbitals
00:07:36.00 so these ones absorb light much less efficiently
00:07:38.22 they've got absorption coefficients around 20,000
00:07:41.22 whereas up here with these long wavelengths ones
00:07:44.01 you can get as high as 200,000
00:07:46.05 so in fact, the longer wavelength fluoros are much better capturing photons
00:07:50.17 and much brighter on a per molecule basis
00:07:53.18 and here is an example of one of these long wavelength
00:07:56.25 this one is a particular favourite in my lab, Alexa647
00:08:01.06 this is a cyanine type dye
00:08:03.01 you can see here this really extended orbital
00:08:05.19 and again a symmetrical, this nitrogen is donating
00:08:09.03 this one is accepting, but they're symmetrical
00:08:11.16 and this is the fluorescent part of the molecule
00:08:14.09 and I will come back to this molecule later
00:08:15.24 and talk about some of the other features of it
00:08:17.28 which are important for practical use like labeling proteins
00:08:22.19 I just want to mention very briefly a completely different kind of fluoro here
00:08:27.13 Qdots, they've become very popular for certain kinds of experiments
00:08:31.25 they look nothing like the molecular fluoro
00:08:33.27 they almost look like a little tiny virus or something
00:08:35.29 inside the Qdot there's a semiconductor nanocrystal
00:08:40.05 it's actually a very special kind of crystal with two different layers
00:08:44.07 of different semiconductors
00:08:46.07 and these semiconductor, these core-shell nanocrystals
00:08:49.26 can be highly fluorescent if the ??? gaps of the semiconductors are tuned right
00:08:55.00 so these can be incredibly fluorescent molecules
00:08:58.09 they are nanometers sized these Qdots
00:09:01.06 so they are more like a small protein in size
00:09:03.16 and then they have to be coated with a bio-compatible
00:09:05.29 this particular one has been coated with a lipid
00:09:08.11 so that they don't interact non-specifically with biomolecules
00:09:13.21 and it turns out with quantum dots
00:09:15.09 you can choose the tune, the wavelength
00:09:18.04 simply by the size of the semiconductor crystal
00:09:21.11 so you can here go from blue to red simply by increasing the size
00:09:26.29 and they have very very tight emission spectra
00:09:29.04 so you can in principle pack more, deconvolve more of them in a microscope
00:09:33.20 amazing with these molecules, they don't photobleach at all
00:09:36.18 so they don't have the same kind of photochemistry I'll talk about
00:09:39.15 so they're extremely bright and they don't photobleach
00:09:42.05 which is incredibly useful for some applications
00:09:45.03 for example, tracking single molecules on the cell surface
00:09:48.03 also in biophysical applications
00:09:51.07 the only downside of these Qdots, they are rather large
00:09:55.06 so you have to figure that into you calculations
00:09:57.08 and also modifying them for labeling proteins is challenging
00:10:01.03 although people have worked on that, that are doing that
00:10:04.16 so, not quantum dots, but the organic fluoros do tend to photobleach
00:10:09.25 as I'm sure many of you are already aware
00:10:12.15 the chemistry here is actually not terribly well understood
00:10:15.20 but the basic idea is that the probe in its excited state
00:10:18.29 can interact with molecular oxygen
00:10:21.06 molecular oxygen is a stable radical and it can interact
00:10:25.10 pick up energy from the excited state
00:10:26.28 and the oxygen can be converted to highly reactive species
00:10:29.28 singlet oxygen or hydroxyl radicals
00:10:32.21 this is OH dot, not OH minus
00:10:34.28 these are highly oxidizing species
00:10:37.01 they can come back and react with the fluoro and destroy it
00:10:39.24 importantly, they can also destroy nearby proteins and lipids
00:10:43.21 so photobleaching and photodamage tend to go together
00:10:47.03 usually we think of them as a bad thing
00:10:49.25 they get in the way of our doing in experimental cause artifacts
00:10:53.10 but there are some experiments where people have put them to use
00:10:56.03 notably in this so-called CALI technique
00:10:58.23 chromophore-assisted laser inactivation
00:11:00.21 invented by Dan Jay a few years back
00:11:02.26 where the basic idea is if you have a protein with a probe on it
00:11:07.24 if you excite that in the presence of oxygen
00:11:10.13 it will actually destroy the protein
00:11:11.25 or in some cases you can destroy a whole cell
00:11:14.03 and it can be used to locally a blade
00:11:15.24 so this is putting the damage to good work
00:11:18.02 and there's a version of red fluorescent proteins
00:11:20.06 so called killer red, which will do the same thing
00:11:24.08 and this part of the chemistry section by say
00:11:27.27 there's been a lot of development on probes
00:11:30.14 but I think that there's still a lot to do
00:11:31.25 and this is sort of an attention chemists here
00:11:33.28 because I think there's still a great deal to be done by chemists in this space
00:11:36.28 perhaps particularly I'll point out here with special properties
00:11:40.12 probes that will switch on and off with different light
00:11:42.29 or switch on when enzymes attack them
00:11:45.12 and that kind of thing
00:11:46.08 so I think a really cool area for people with an interest in synthetic chemistry to think about
00:11:52.15 ok so that's the probe itself and its fluorescent properties
00:11:56.22 now I want to talk, of course, we care about attaching the proteins
00:11:59.29 because in most applications people are attaching this probes to a biomolecule
00:12:03.23 usually a protein, sometimes a nucleic acid
00:12:07.12 I'll only talk about proteins
00:12:09.07 and there's really two amino acid side chains we have to worry about
00:12:13.02 or think about for proteins
00:12:15.00 and I'm gonna use the single letter abbreviations
00:12:17.22 so C is cysteine - SH, and K is lysine
00:12:21.18 cysteine labeling is ideal for site-specific labeling
00:12:25.14 if you can engineer it or nature gives you reactive C per protein
00:12:30.10 lysine is a much more common amino acid
00:12:32.20 most proteins have a lot of lysines
00:12:34.17 and this is ideal for general purpose labeling
00:12:36.25 you can a few lysines on most proteins without losing activity
00:12:41.04 so an important point for both these protein nucleophilic amino acids
00:12:47.04 is they're only reactive in their deprotonated form at a high pH
00:12:51.18 cysteine is reactive as a thiolate ion above pH 8
00:12:55.08 lysine is reactive as the free amine
00:13:01.04 although, you only completely deprotonate lysine about pH 10
00:13:05.06 you usually do lysine labelings around pH 8 or something like that
00:13:09.12 there's enough unprotonated lysine to react
00:13:13.24 these two nucleophiles have very different properties
00:13:16.21 so we can distinguish them with different probe chemistry
00:13:19.26 the thiolate ion, cysteine here, likes to react with these kinds of electrophiles
00:13:25.19 so classically people would use iodoacetamide or ethyl maleimide
00:13:30.03 this is a so-called Michael acceptor to label protein
00:13:33.23 and the same chemistry, which goes back many years in protein chemistry
00:13:37.15 was adapted to fluoros
00:13:39.13 so here are two typical thiol-reactive probes
00:13:43.10 this one up here, pyrene iodoacetamide, has an iodoacetate
00:13:47.17 that the thiolate attacks
00:13:49.10 this one has a Michael acceptor
00:13:52.25 so that's cysteine
00:13:55.10 the unprotonated form of lysine is what people call a harder electrophile
00:13:58.25 it prefers to react with SP2 carbon electrophiles
00:14:01.22 particularly reactive carbonyl derivatives
00:14:04.02 where X here is a good leaving group
00:14:07.26 and you want a leaving group that leaves well but not too well, like chloride
00:14:14.09 because that would react rapidly with water
00:14:16.07 and a lot of probes now use this N-hydroxysuccinimide ester
00:14:19.29 which has a reasonable balance between being stable enough
00:14:23.16 it's not immediately hydrolyzed in alkaline solution
00:14:27.18 but reactive enough so it rapidly reacts with lysine residues
00:14:33.06 so here is this come back to the probe I mentioned before
00:14:36.15 Alexa647 to highlight a different feature of this
00:14:39.12 I've talked about the orbital before
00:14:40.27 but this is the protein labeling part
00:14:43.05 and you should be able to recognize that this is an N-hydroxysuccinimide ester
00:14:48.08 the lysine attacks at this carbonyl and kicks out this NHS portion
00:14:52.24 so this is a lysine reactive probe
00:14:55.04 and the one other thing I wanna point out
00:14:56.29 a lot of modern probes have these sulfonic acid groups
00:14:59.23 there are four on this one
00:15:01.06 and these are not reactive, they are just present as a sodium or potassium salt
00:15:05.18 and they are there to make the probe water soluble
00:15:08.20 and prevent it sticking hydrophobically to a protein
00:15:10.26 this one has four, it's more common to have two
00:15:13.23 but in my lab's experience almost always you want a probe with some of these sulfonic acids on them
00:15:20.09 they much better behave, they are just less sticky, in general
00:15:25.03 ok, so that's labeling amino acids
00:15:29.14 with cysteine, you can often target a one particular amino acid
00:15:34.17 but if you really want to label a protein in one place accurately
00:15:38.12 and know exactly where that place is
00:15:40.07 there are some other modern technologies for doing that, that are very cool
00:15:43.29 SNAP, halo, and FLASH tags
00:15:46.17 and I think there are other methods being invented all the time
00:15:49.00 the basic idea here is
00:15:50.21 that you genetically engineer your protein
00:15:52.26 you put some tag on it
00:15:54.24 will then act as a kind of synthetic acceptor for the fluoro for covalent reaction
00:16:01.10 I will show you the chemistry here in detail for the SNAP tag
00:16:05.00 here we are using a substituted benzylguanosine
00:16:08.19 and this part here of the fusion protein
00:16:11.01 is a modified DNA repair enzyme
00:16:13.26 that evolved in nature to remove benzyl groups that happen to get on DNA
00:16:18.07 it's been mutated now, so it reacts but can't unreact again
00:16:22.19 and so, these authors developed this as a really efficient labeling method called a SNAP tag
00:16:29.28 the halo tag is a comparable method that uses an alkyl halide derivative
00:16:35.13 so these are ways where you genetically engineer your protein
00:16:38.18 and you know exactly where the fluoro will go
00:16:40.26 they work well in cells
00:16:42.09 they also work well with pure proteins
00:16:45.06 and finally, a really cool piece of chemistry from Roger Tsien
00:16:47.24 who's kind of the hero of fluorescence in biomolecules
00:16:52.25 this FLASH molecule, this is fluorescein with two arsenic groups on it here
00:16:57.04 and arsenic likes to bind to thiols
00:17:01.15 and Adams and Tsien developed this FLASH probe
00:17:05.13 that will, with very high selectivity, bind covalently
00:17:10.01 to four cysteines engineered into an alpha helix
00:17:12.29 and I'll leave the reference on that
00:17:14.16 for people interested, it's a very elegant targeting chemistry
00:17:17.25 and I will end here by talking
00:17:20.07 not all probes are targeted covalently
00:17:23.04 it's often very useful to have probes
00:17:25.02 that target with high affinity non-covalently
00:17:28.06 they can be easy to use
00:17:30.16 I will show you just one example here
00:17:32.26 here is a cell stained
00:17:35.03 it's probably a fairly familiar image to cell biologists
00:17:38.17 with DAPI to stain the nucleus blue
00:17:41.00 and rhodamine-phalloidin to stain the actin filaments red
00:17:44.09 I will just show you how the rhodamine-phalloidin works here
00:17:47.07 as the name implies, it's a bifunctional molecule
00:17:50.18 this is the rhodamine part
00:17:52.01 a fluoro which excites in the green area at 546
00:17:56.17 and then this a certainly more complicated piece of molecule
00:17:59.11 here this bicycling molecule is a toxin
00:18:02.15 phalloidin, from Amanita phalloides, the poisonous mushroom
00:18:06.02 the death cap mushroom
00:18:07.07 and this part binds very tightly to actin
00:18:09.27 so this bifunctional molecule will find actin filaments
00:18:13.07 and bind very tightly to them
00:18:15.20 you can make fluorescent derivatives of other drugs as well
00:18:19.05 it's a very useful way for localizing receptors
00:18:22.07 I will end here on organelle probes
00:18:25.26 which is another non-covalent targeting method
00:18:27.24 here's a pretty image of a cell again stained with DAPI
00:18:30.29 but the mitochondria have been labeled red
00:18:36.08 here as the sort of wormy looking structures
00:18:38.02 and the lysosomes have been labeled green
00:18:41.02 and these probes are just making use of the physical biochemistry
00:18:45.08 both mitochondria and lysosomes pump protons
00:18:48.23 but in the case of mitochondria
00:18:51.03 what ends up is not as a pH gradient so much as membrane potential
00:18:56.17 and lysosomes is actually a pH gradient
00:18:58.10 and you can use this proton pumping to specifically target these organelles
00:19:02.13 here's a Mitotracker dye
00:19:04.25 that was used in that image
00:19:07.05 this is very like a rhodamine dye
00:19:09.28 but has lost the carboxylic acid here
00:19:11.20 so this has a delocalized positive charge this molecule
00:19:14.11 it's lipophilic, has a delocalized positive charge
00:19:17.14 so it follows the membrane potential
00:19:19.06 and enters mitochondria
00:19:21.18 and then this part here, this chloro group
00:19:26.07 makes it react to the thiols
00:19:28.19 so it will actually get trapped inside the mitochondria
00:19:32.08 and finally I wanna end here
00:19:34.22 sorry I'm blocking one of this molecules but I will step off the screen in a second
00:19:38.26 there you go
00:19:40.11 here is three molecules for you to think about
00:19:43.12 and I'm not going to tell you the answers here
00:19:45.27 but if you are interested
00:19:46.28 try to think about what kind of wavelength would you predict these molecules fluoresce at?
00:19:50.27 will they react with proteins?
00:19:52.17 what other chemical properties can you note about them to predict their behavior
00:19:57.28 the one I have to stand off here to look at
00:20:00.16 this one it's gonna be a bit hard and it's kind of a trick question
00:20:03.26 but if you compare it to the low pH form of fluorescein you may be able to figure it out
00:20:08.13 and, I don't know, I hope especially for those of you who
00:20:12.14 might be a little afraid of chemistry
00:20:14.12 I hope this will convince you that is actually fun to look at molecules
00:20:17.24 and If you make a habit of it
00:20:20.07 they will talk back to you
00:20:22.00 thank you

This Talk
Speaker: Tim Mitchison
Audience:
  • Student
  • Educators of Adv. Undergrad / Grad
  • Researcher
  • Educators
Recorded: July 2012
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Talk Overview

This lecture describes the chemical properties of organic dyes and quantum dots (Q dots) that make them fluoresce and how their fluorescence wavelength is tuned. It also describes how dyes can be attached to proteins, photobleaching, and other dyes that bind DNA (Hoeschst) or organelles (mitotracker, lysotracker).

Questions

  1. True or False. A larger extended orbital of a fluorescent dye will result in a bluer shift of fluorescence.
  2. Which of the following is true of fluorescence dyes?
    1. A more flexible dye structure will result in brighter fluorescence.
    2. Dyes with similar electron donor and acceptor at opposite ends of the molecule reduce quenching and creates a smaller stokes shift.
    3. Shorter wavelength fluorophores tend to have higher extinction coefficients
    4. Addition of sulfonate groups to a fluorophore makes them more membrane soluble.
  3. Which of the following is the best answer for Qdots compared to fluorescent dyes
    1. Qdots are smaller in size and brighter
    2. Labeling a protein with a single Qdot is significantly easier than with fluorescent dyes.
    3. The fluorescent emission of Qdots can be easily tuned by varying its diameter.
    4. Qdots tend to photobleach more than a good fluorescent dye
  4. An excited fluorophore can pass energy to molecular oxygen to produce what two damaging reactive species?
  5. The technique CALI stands for ______________________ .
  6. What are the two most common amino acids used for covalently attaching fluorophores in proteins? Which one is the most common?
  7. Name a common reactive group for labeling lysine residues? Which pH is most suitable for labeling- pH 6 or pH 8?
  8. SNAP, HALO and FLaSH are genetically encoded tags for covalent reaction with a fluorescent dye. Which is the smallest?

Answers

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Speaker Bio

Tim Mitchison

Tim Mitchison

Tim Mitchison completed his undergraduate degree in biochemisty at Oxford University before moving to the University of California, San Francisco to do his PhD with Marc Kirschner. After a brief post-doc at National Institute for Medical Research in London, Mitchison returned to UCSF as an assistant professor in 1988. In the late 1990s, he moved… Continue Reading

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iBiology and iBiology Courses are part of the Science Communication Lab (SCL). Our mission remains the same, to connect people to science. However, our focus has shifted to producing and evaluating cinematic films for education and the public, which you can find on the Science Communication Lab website. For more information, please see this blog post!