Biology 1A - Lecture 26: Emergent Properties: Multi-cellular

Uploaded by UCBerkeley on 29.10.2012

>>INSTRUCTOR: Good morning. Let's get started. My name is David Weisblat and I'll be your
companion through this last third of boy owe 1A, the material we're going to talk about
as indicated in lecture is animal form and function.
And you see from the outline and if you start looking tat chapters there's a huge amount
of material that could be considered in this section. And what I wanted to do today sort
of by way of introducing myself and there's not Chapterハ40 is a little bit of a hodgepodge
also so, we're just going to talk about things in general and see how you mightハ what strategies
we might take to organize this huge amount of information.
So, just first to go over the logistics are very much the same as what you're use to.
I'llハ this is the first time I've given this course.
And so my lecture are not prepared, yet I'm still working on them reading the book along
with you, this may have a good points and its bad points but that's what we're doing.
So endeavor to have aハ at least some rough draft of the lecture posted the night before.
And then, during the night I'll see what actually happens and during the lecture, we can then
revise the notes if needed if there's material that I don't get through.
And sorry for the confusion, the homework as before isハ I'll be posting it as soon
as I can figure out what it is, and it's due at the start of the lecture after the one
where it's discussed. And then I know some of you are interested in exams and grades.
The exam questions will concentrate on the material covered in the homework and whatever
it is we talk about in lecture. Okay. So, one of theハ how do we deal with all
of this information? What are we doingハ it use to be 100 years ago that, you know,
you would have 1 class in zoology, one class in botany and that was pretty much it.
Right. So you could learn everything.
Medical students in the beginning of the 20th century, they learned all there is about medicine,
they learnedハ you know, anatomy, they learned the names of a few drugs and used them, you
learned everything about a subject. Now, obviously there's been such an explosion of information
that's no longer possible. We have our external brains in the form of computers, all resources,
the Internet, but what is it you're supposed to have in here then? I just wanted to play
you this clip fromハ let's see, to show you how cool I am with the Internet and everything.
So, how do we organize knowledge and know what we know? Here's one approach...
Wrong. Hm? This is supposed to link toハ okay.
That's not working. This is supposed to be a hyperlink.
There it is. >>STUDENT: [Indiscernible]
>>INSTRUCTOR: Huh? >>STUDENT: [Indiscernible]
>>INSTRUCTOR: Command? Gosh, this is fun, I've got all of these smart people here.
Command, huh? Whoa!
Thank you. [Applause]
[VIDEO] >> I don't understand it, all of that talk
about evolution and biology, big bang theory and all of that is [Indiscernible]. It's lies
to try to keep meaning in all of those taught that fromハ
>>INSTRUCTOR: So I'll just get that again. Ready?
[VIDEO] >> [Indiscernible] I don't understand it,
all this talk about evolution, and biology, big bang theory and all of that is last trait
of [Indiscernible]. >>INSTRUCTOR: Okay. So that's one opinion.
(No sound). So, it's interesting, I was really struck
by this comment because this gentlemen in this one sentence got the 3 things that are
really most exciting to me as a scientist and then evolution a big bang and embryology,
and it's my life's work to think about how these things are connected to each other.
He thinks they're all lies, straight from the pit of hell.
This man representative Paul Brown he's a representative from Georgia, 10th congressional
district, he also explained his reasons for voting against climate change legislation
as, you know, well it's just the manmade global warming is a conspiracy perpetrated by the
scientific community. So it's sort of a fringe view. What does he do? He sits on the committee
on science and technology, including subcommittee on energy and the environment.
And he's running unopposed for reelection. So, its justハ a different way of thinking
about things. And you can draw your own conclusions, I guess.
So, for me, I grew up in Michigan. In a place where there was pretty open sky,
not much light pollution, I go for walks at night and think about look up at the a stars
and contemplate my own insignificance, and wonder what it all meant and how to make sense
out of things and what to do with my life. And eventually, it comes down to me to try
and put things into perspective, I always like to start at the beginning of my classes
to pretty much anything that I start to talk about, eventually it reduces to the big bang.
Here'sハ because everything that we're doing, everything that we've, huh, considered, what
we've been, what we will be is part of the universe, where did that come from? It's always
going back to what's the explanation for things? Well, there's been a lot of physics done,
Professor Phillip Panco(?) and others have concluded that the universe initiated as this
big bang, this tremendously dense concentration of stuff, it was so concentrated, so dense,
so hot that light and matter the rules of physics didn't even exist at the very beginning.
How can you actually study what was going on there at these very high energies?
Well, that's what high energy particle physics, when they're accelerating particles towards
each other, the speed of light they're getting they're infinitesimal periods of time, the
high energy that was mirroring what was going on at the very beginning of the universe,
not very beginning, they can get back to about 10 to the minus 35th seconds, and in the period
before that, between 0 and 10 to the minus 35th seconds, physicists still don't have
much of a clue of what's going on. From that point out, you have these quantum fluctuations
that's easy for me to say. And you can haveハ by the time of microsecond
had passed, matter and energy were distinct and particles for starting to form so you
have ionized, you know, protons, electrons and newtons and shortly after that the universe
had cooled enough to protons and electrons could come together to form hydrogen atoms
so you had this vast cloud of gas still rapidly expanding but there were variations, there
were fluctuation, it wasn't uniformly dense, and so the locally more dense areas started
to condense, as the law of gravity kicked in, and the rest is stars, galaxies, and eventually
the supernova that formed heavier elements, those could condense to form planets, and
then there's all takes time, but after about 10ハmillion years or so, on at least 1 planet,
on at least 1 star, this biological life as we know it came into being.
Okay. And since that point in the last 3ハbillion
years, things have progressed further and here we are.
So, we don'tハ this is another just like the very origins of the universe the 10 to
the minus 35 second is a mystery we don't have much of a clue about how life actually
began. But, from that point, we're getting a better
and better picture of how life has evolved. Okay.
And that's the sort of question that interests me now, how you get all of these different
kinds of animals. But it's still the fundamental thing for me
is that this is all a continuous process, cosmic evolution leading to biological evolution,
leading to biology 1. So, in the thinking again about at a very
broad level, I come to define 2 different types of processes.
And one, I call anhistorical process. What is anhistorical? What does anhydrous
mean? This is all from Greek, anhydrous means without water.
Okay. And anhistorical process is one that a process
that has no historical component, or very little.
What do I mean by that? Well, let's think about the example of hydrogen
formation for example. First, I think you'll admit that it's highly
reproducible you can take a proton and electron and as long as they're a reasonable energy
they'll come together and form a hydrogen atom.
And it doesn't depend, minimally contingent, contingency is extent to which one thing depends
on something that came before it. Okay.
That's contingency. So, in forming hydrogen atoms, there's not
much contingency, it doesn't matter where the electron has been whether it's from a
lettuce leaf or a star it doesn't matter from the proton comes from, as long as they come
together in the right angle and right energy you're going to get hydrogen.
And this is literally now a universal process this has been going on since I said 10 to
the minus 6 seconds after the initiation of the universe, and it's still goes on today.
We're pretty confident that the same process that we can see on earth or in the sun is
going on the other side of the universe as well.
Oh, okay. >>STUDENT: [Indiscernible]
>>INSTRUCTOR: Right, that's what they said. (No sound).
iPhone silent. >> It has to be off.
>> Oh, yeah. >>INSTRUCTOR: This is why the first lecture
is sort of practice, right? Uh oh. I've got it [Indiscernible].
[Laughter]. That goes there. That goes there.
And I know I'm going to rip this off about 73 times during the lecture. Okay.
Sorry. Yeah, [Indiscernible].
So, back to this anhistorical process of hydrogen formation, because of its reproducible and
universal and minimally contingent it's obviously subject to the analysis by the scientific
method, right? We can repeat it, we can change the variable, the energy the angles whatever
you want. And study it and make all sorts of predictions about how this process works.
No brainer. So let's contrast that with a euhistorical process, a truly historical process,
for example the story that each of us brings with us as to why we're here today.
So, you know, we each have a unique story, my [Indiscernible] not big enough.
Actually, there are a lot of people think that I shouldn't be here today. I taught a
course like this way before you guys were born about 30 years ago called Zoology 10,
it was famous course taught by a famous professor, famous [Indiscernible] professor and when
I was a brand new assistant professor, somebody in they're wisdom thought I should take over
this course. And I did that, and I tried to make clever
quizzes and I started with the big bang and talked ability chemistry and quantum mechanics
that I thought if Zoology 10 was the only biology course, the only science course that
somebody was going take, they should be exposed to how these things interconnected. And I
didn't want to insult the brilliant Berkeley students I had, you know, challenging questions,
not just memorization stuff but things you can really think about on the exams, and the
grade distribution or the beautiful bell shaped curve centered at 50%.
[Laughter]. And I didn't bother giving any practice questions
or stuff like that, I just through out these exams at the end of the thing.
And at the final exam, there was aハ there's a petition circulated [Laughter], that was
delivered to the chairer of the department of zoology, which is where I was then. Stating
that I should not be allowed toハteach or work or do anything else on campus.
And this is in the days before social media or anything, there was this spontaneous, I
mean, over half the class signed this exam. This petition.
So, that's my story. Taking 30 years ofハhard work that I've clawed
my way back here and we're going see how things go in these next 12 lectures.
[Laughter]. So, and now, we have I don't know if any of
you on members of knew but there's all sorts of online petitions so it should
be easy to get, much more engagement than that. So this is a euhistorical process this
not just my story, it's irreproducible, you couldn't really turn back the clock and do
it again, because it's so highly contingent, how did I even get a job at Berkeley in the
first place right? All of these little things what if I grew up somewhere if there weren't
stars or what I had taken my father's advice or gone to medical school you would have been
spared this. So it's contingent on the details of my life, what if my 2 sets of grandparents
had not migrated from Sweden and Russia representatively, what if my father's father died in a [Indiscernible]
instead of escaping to work in a junkyard in Ohio. So the other thing is, that these
stories, whatever your story S it's sort of local, right? It's you, it's here, it's now,
they're almost certainly now we think other planets with other life forms, but probably
not just like this one and the people on it probably aren't just like we are.
And therefore, how can you study history? Well, you study history more by retrospection
thinking about what was going on at various points of those times and sort of trying to
make sense of a story in retrospect rather than trying to be able to predict things.
So these are two different types of processes. Now, here's an iClicker question to see if
that works. So, given that we have these two, euhistorical
process and anhistorical processes how would you classify biological processes? Here you
can anything, sell the vision, or thermoregulation, like we're reading about in this chapter,
according to these various criteria, where would you put biological processes?
And now, I need to do this... And what do you think about 20 seconds?
30 seconds? Okay.
How do I stop it? And how do I display the answers?
Like that? Excellent.
So, I thinkハ the way I think about it is thisハ now, how do I get rid of that?
What? There? No. Click the bar again.
This bar again? Okay.
Geez, you guys are good. So, what do you think?
Biology, biological processes are reproducible, right?
And they are subject to analysis by the scientific method, universal? Uh, I don't think there's
any argument to be made that biology is going on all across the universe it certainly hasn't
been going on until a few billion years ago here on earth so it is not universal in that
little sense. And I would say it's quite contingent, it depends on the processes of how evolution
occurred. Where is it written that there are only these 20 amino acids?
Where is it written that they all should be in el configuration? Or that, you know, it
should be D glucoseハ so there's all sorts of thingsハ so it's sort of a mix of these
two things, okay. But we canハ we canハ we can do experiments and that's what makes
it fun. Okay.
So, there's always wonderful kinds of life. Just amazing.
And we can think about how has this tremendous diversity of animals, in my case, that's my
interest, evolved. And obviously, it is evolution and that thing
is getting in the way. Move it over here.
So, I think you know fromハ everybody's had bio1A. Evolution, that's the easy part, so
evolution proceeds byハ sorry. You haveハ sort of 3 things going on that
you have excess reproductive capacity so there's a lot ofハthings that have to die, okay.
You have a source of heritable variation that you talked about with Dr.ハFischer, and then
from that you have a selection, of various sorts for re differences in reproductive fitness.
And this gives rise to all sorts of variation, okay, and changes in the animal kinds, and
at the molecular level, the variation occurs from changes in genes and corresponding changes
in protein structure. So how rich is this variable? Let's get an appreciation ofハthat,
so here's anotherハiClicker question, I think they're really easy so, if you take, what
variabilities if you have an amino acid sequence, that you've got the N terminal, amino acids
1, 2, 3, etc., so 350, at the C terminal, given that there's 20 different amino acids
at each position, how many possible protein sequences are there?
And you've probably done it by now, let's another 20 seconds.
Everybody done? Let's finish up.
Oh, please. Okay. Finish. Finish. End. Stop.
Okay. All right.
So, what's the answer? >>STUDENT: [Indiscernible]
>>INSTRUCTOR: D, right there's 20 amino acids at each position, oops, wrong. Well we don't
want to embarrass anybody, we'll just go right ahead.
Yeah, it's 20 to the 350th. Okay. And that's a huge number.
What is the number of atoms in the universe? Atoms in the universe?
10 to the 80th, okay. So, what this isハ what I'm pointing out
here is thatハ and this is just a single protein. So, there's no way that we can actually
explore all of the different probabilities forハ that are open to an evolving system.
And if you think of some organism or population with genes and proteins at one point in some
sort of multidimensional space, as soon as it steps away with one little evolutionary
step, right? There's so many dimensioningハ going along any one of those dimensions the
chances of going off in some new direction from there, rather than coming back to where
it was, are so tremendously high, right, so that there's a continuous process of evolution,
you can't go home again. Okay. So, and that leads to this issue of, you know,
that things keep die verging, okay, that's part of the arrow of time of the history in
the universe. So, that said, is there anything, you know,
why don't we see animals with wheels? Right? Why aren't there examples of any different
kind of animal that we can imagine, I think the answers to that that it is first sort
of contingent, it haven't got there yet, evolution is not start from new process each time but
it's always building on whatever was there before. And the other thing is, that there
are all sorts of important constraints on what is compatible with life and biology as
we know it. And these constraints can be illustrated actually,
also in the process of evolutionary convergence meaning that there are pressures brought to
bare on evolving systems they confront a particular set of problems in the environment and there's
only so many ways you can deal wit. So the one of the examples that came out in the book
is that the question of how animals adapt, or evolve to swim rapidly through a viscus,
medium line water and they develop in different lineages, these very fusiform streamline shapes
to minimize drag and allow themselves to go quickly.
Okay. So, what we're going be talking about in these
lectures here, is the question of how multicellular animals carry out the essential functions,
nutrition, respiration, defense, regulation of whatever it is they regulate, reproductions
and development, sensation and behavior, how do they interact with the environment.
How do multicellular animals do all of these processes that are also carry out to some
extent by the unicellular life? So, what we'll be seeing is the important
part of this, as you go fromハ what didn't show up here is that what we see, you can
think of a cell and you can study cells, all you want and you know just how they reproduce
and how they carry out respiration and everything like that and you know a lot about these single
units, but then when you go to multicellular life, of whatever sort. So, multicellular
life we've got all of these new features that are emerging.
[Instructor writing on board] So, and this can emergent properties you should
Google this, read about it, it's a feature, again, of the sort of universal relevance,
you think about in terms of chemistry, you can study, again, having exact solution for
hydrogen atom, in terms of the Schroder equation, but by the time you get up to carbon you're
already having to start to make approximations and you can imagine is the structure of DNA
or the existence of DNA predicted from the Schroder equation? No.
And similarly when you start looking at multicellular organisms in terms of the things we see all
sorts of new features emerging, okay. In particular, you have cells organizing together
this cooperative behavior that's essential for multi similar life gives rise to specializations
to carry out these different physiological processes.
And an example here, is the one of gas exchange at the single cell level, the plasma membrane
is so thin that oxygen and CO2 can exchange back and forth readily all parts of the cell
are accessible to these processesハ to gassy exchange, excreted products can diffuse out,
but as soon as you start going to more complexハ animals, you have problems start to emerge.
Even in this hydraハ it's sort of constrained by the fact that it doesn't have a fancy circulatory
system so it actually can only pretty much exist as a two layers of cells. So you have
an inner layer, this mouth digestive tract opening where food is digested, under digested
is spit back out there's no anus or anything and then you an outer layer of cells with
some specialization. And not much else. There's no distinct mesoderm, you an inner
layer and outer layer, but these cells are what with call epithelial, and that's the
example of emergence tissue eventually organize ever organization as you go from cells to
organisms. And you read about the four main types of
tissues in the body, the nervous system we'll be talking about quite a bit and muscular
system later. Connective tissue is sort of curious to me, the idea that it's cells that
are embedded in a matrix of a material that's defining feature. And that could be the properties
of the connective tissue then are highly dependent on what that matrix is, whether it's tough
elastic molecules or liquid as in blood., etc. And then the fourth type of tissue that
we see in is epithelial tissue, which is sort of neat.
So, there's different layers, organisms, epithelia are these layers of cells that are in close
contact with each other. They could be very thin layers, columnar layers,
cuboidal layers, and/or multiple layers, okay. And they line almost not only the outside
animal but most of the internal structures as well.
Okay. So, the epithelia we think of them, mainly
to in terms of skin in terms of generating a barrier to invasion or evaporative loss
of things, also in the gut, the epithelium is highly specialized for transporting nutrients.
In my area, theハ what'sハ which is developmental biology the epithelial layers are wonderfully
involved in making embryo's take on different shapes, you can have
a single layer of cells and because of the connections and the coordination of behaviors
between these cells, around they're structural links, so it'sハ there's a structural links
and there's coordinating behavior. You can have epithelia undergoing a motion called
evolution. They can also go into a make a pucker. I can't draw that. So you just make a pouch
there. Called invagination.
Various types of movements that you can imagine. And then there's another one called: Convergence
and extension. And that's where you have a layer of cells
that say initially one shape and by rearrangement, you can get a dramatic change in shape of
a tissue by rearrangements of cells insideハthat epithelium.
Now, this is an accurate drawing what usually happens in this case, is you have epithelial
cells tend to be in roughly hexagonal arrays, and theseハ the epithelial cells that you'll
see can change shape, they can undergo constrictions along they're edges.
So, if you have, for example, thisハ these pair of cells, A and B, undergo constriction,
that brings cells C and D into proximity, this is called a rosette formation.
So, you can have four or more cells depending on which cell boundaries constrict, you can
bring these cells together. And then when this relaxハ if this relaxes a long the opposite
orientation, you can have wa, wa, wa. You can have cells C and D become neighbors if
you now constrict here and then relax this way, you have C and D become neighbors and
A and B are isolated. So, going from here to here, you've had a
neighbor swap, C and D which were not neighbors are now next door neighbors by this rose et
formation and relaxation, so that's just a layer of the sorts of things that can go in
terms of the dynamics of the epithelium, and what's amazing is thatハ (No sound).
And still the epithelia itself still maintains its complete integrity, and remains, resistance
to the diffusion of the molecules across the epithelium.
So, going a little further if you look at the epithelia, they're also polarized, meaning
you have an apical surface, this is the surface that would normally be facing the outside,
whether it's the outハside of the skin, or the lumen of your gut or digestive tract that's
the apical surface that's facing that, and then on the sides and bottom you have a basal
lateral surface. So, you have an apical surface.
And then a basal lateral surface, okay. And these are separated by various sets of
junctions, near the apical surface. So, here we're going goハ on the next slide
we'll take a look at this that theseハ there's all sorts of this cell/cell junctions that
are part of the epithelia that provide mechanical strength and yet the possibility for changing
neighbors, the regulation of material flow across the epithelium, and also the potential
for material flow within the plane of the epithelium.
Okay. So, these areハ some of the junctions you
see. There are in terms of making theハ thisハ these individual epithelial cells into a mechanically
intact sheet that can fold over and roll over and stretch and contract, you have adherens
junctions, special sets of membrane proteins linked across the cell/cell boundary and linked
within each cell to the actin cytoskeleton. Also there are desmosomes that are linked
to the intermediate filaments the third type of cytoskeleton so you have microfilaments,
intermediate filaments linked to adherens junctions and desmosomes. And then you have
gap junctions, these are transmembrane proteins in each adjacent cell, hexamers of proteins
that form actually a cytoplasmic bridge that connect with the proteins on the other cell
surface, and provide for a cytoplasmic bridge through which molecules can freely diffuse
as long as they're of a molecular weight less than around a thousand or 2,000, something
like that. So diffusion of materials between cells in they're epithelium, and finally there's
this third type of junctions the tight junction, which is right up there at theハ this is
sort of the barrier that defines between the apical surface and the basal lateral surface.
So the tight junctions, again it's a yet a different kind of proteins that interlock
with each other, really tightly at this surface, like the two sides of a Ziploc bag, and depending
on what tissue you're talking about, these have different properties, but they can be
highly resistant to the diffusion, even of water molecules, you can do experiments with
radioactive, you know, [Indiscernible] water, and show that it cannot diffuse across certain
types of epithelial in types of fish, fish embryos who are having to deal with fresh
water [Indiscernible] environment, they maintain they're constant by having very tight junctions
in they're external epithelium, and yet while retaining that highly resistant diffusion
barrier, these cells can still be changing positions to give different shapes to the
embryo in embryogenesis. So, theseハ there's a tendency to view these
junctions as fixed and static, but they're highly dynamic processes.
Okay. So, meanwhile, a general feature that we're
going be dealing with in animals and coming in the chapter is this process called homeostasis,
the regulation of one or more internal factors by negative heed back. Okay. And that typical
variables that are subject to this are body temperature, internal pH, oxygen or CO2 levels
in the blood, things like that. Okay.
And for each of these different variables, an animal, may be regulating that or may not.
Okay. It's not an all or oneハ all of none proposition.
So they may regulate one factor to another. The ways in which these regulations are achieved
are many and varied it depends on what it is you're varying it depends on the animal
that's doing the varying. So what we're talking about here is, sort of a higher level, an
operational level idea of what's going on in animals.
So, before you jump into all of the details. You can have regulation of temperature by a lizard, you
know, go out in the sun, they'll go in the shade, the set point may vary.
And an example of that is shown in this example of mammalian thermoregulation, you have body
temperature that's maintained you a sensor in the hypothalamus and if youハ if that
detects at a higher temperature than what itハ the set point is, you can have physiological
responses such as sweating or vasodilation in the skin to circulate more hot fluids to
where they can cool by convection. Okay. And these responses normally would lead to
a decrease in body temperature. Okay. Similarly if you have a decrease in body temperature
you can have vasoconstriction, shivering, things like that, that generate work and burn
energy to increase the body temperature. Okay.
This is not a single set temperature, right, you have diurnal variation in the circadian
variation in your body temperature, coldest is just before you're waking up.
Disease states can affect the set point. Okay. So, fevers and things like that.
As the final consideration we'll have to talk about is this the idea of metabolism and the
energy consumption there's all sorts of things involved, processes, it's sort of a thermodynamic
thing you're generating heat and people wondered for a long time, what sorts of laws or generalハ
whoops. Generalities could be made there wonder how I did that.
So, what can youハ how can you measure the metabolism? Basal metabolic rate? You measure
all by the overall heat production, put an animal in a calorimeter or more easily you
can just measure since it's all involving energy, metabolism and respiration you can
measure oxygen consumption or CO2 out put and you can do this under defined conditions,
post eating and resting and the text then says that from organisms raising in size from
bacteria to blue what else the metabolic rate roughly proportional to body mass to the three
quarter power, is that really true? So here's the scales.
And itハ here, I just wanted you to thinkハ the idea here is to think about what you're
reading so here they define basal metabolic rate leaders of O 2 per hour. And now here
they have basal metabolic rate again when they're trying to compare different size animals
they're still calling it the basal metabolic rate but now its leaders of OT per hour per
kilogram so that's a different unit so at the very least they should be talking about
mass specific things of metabolic rate and there's another factor, is that this law is
not really a law. First of all, if you put things like amphibians or remember tiles on
here they have a much lower metabolism for the weight and also there have been studies
that have looked at this question and decided that thisハ the guy who made this law in
1930, or so, had some serious mistakes and that the basal metabolic rate is actually
proportional to body mass, to the two thirds. Why is this important?
Well, if you want to think about explaining why something is case, why is it?
Why is it the case that it should scale to the three quarters or should it?
If it's actually scaling to the 2/3 power these are different considerations that you
need to take into account you can take a look at this paper and realize even how something
simple as this gets complicated in terms of the statistics and various complicating factors.
So, you should not take the text as a bible. Be critical of what you're thinking and what
you're reading and certainly what you're hearing from me.
See you next time.