Add to Watchlist

Lecture 24. Enzymes


Citation of segment
Embed Code
Purchasing a DVD Cite video
OK organist .period talking about enzymes
1st this is the
histogram for mid-term too it's
very impressive 1 of 2 things happens if you guys did a really good on June marking Stephen got paid off by a large number of you to graded easily I don't know which which it is but these are all
ayes over here it's only the smaller number of these are hardly any cities OK so this is
the 1st time I've been a professor and 24 22 years before the 1st time the meeting on the
exam has been an mean was like right here it's never happened before in 1 of my classes
where the meat on a midterm exam isn't a no so there's really really well and I didn't think the exam was particularly easy I really didn't now what is all this
mean for your future but this is the how like doing schoolwork calculated couple days right I dropped year
to lowest quizzes to calculate the I dropped it OK so your quiz your quiz average could still go up a little a down a little based on what you did today but basically it looks
great rightly all these days but only and all these people over here but pretty well you
folks don't give up right there's
a 200 point final right so far we have fixed the quizzes are worth 200 meter 1 was worth 100 meter to is worth 100 so we fixed 400 points in the courts nothing we can do about those 400 points right now right we've taken those border points we've engraved them in stone but we haven't said anything about the last 200 points that's 1 3rd of all the points in the class are still going to be decided on that final exam so this
person right here and can move down this person right here can move up these folks over here are getting an A-minus they might be able Palatinate these people over here getting a B plus they might be able across all over this be barrier To get an a
minus what's of movement within this histogram is still possible right that's the message I want send to you so if you're getting worn down at the end of the school year ends June 1 you know can you possibly carry on for another week I'm I'm going to implore you to focus on the final exam try to do well but they now maybe for most of you just doesn't matter you've gotten into whatever grad school you're going to get into work Professional School Medical School pharmacy school you got a job lined up for the summer whatever it is maybe it doesn't matter to you and for those of you who are in that situation do whatever you feel you need to do I don't blame you I personally did not work that hard mice spring quarter of my senior year I decided I did really work that hard but for those of you who care how many people really care but the
great to be in this class for whatever reason rational or a rational and you can still change of
great everybody had their hands up and everybody who didn't too but no I don't take my word for
this ah I calculated this and somebody sent me an e-mail said you know my home my doing
scores all messed up a lovable on I went into the spreadsheet may double checked and I don't think there's any mistakes in the spreadsheet but let me show you
what I did I took your for for-hire squeeze multiplied by 8 because the quiz agreed from 1 to 5 so that 4 times 5 is 20 times 8 is
160 quiz points not including only 2 today of course 160 quiz .period plus 100
plus 100 is 360 right that's I
calculated your home I do score right so this is the percentage of your told points where
each quiz worth 40 points OK but thought so don't take my word
for it check your own home I doing score because this spreadsheet I'm only going to add 1 column to it minimum calculator final grade from that write this spreadsheet is your final grade once I had the final exam that includes 7 also OK so it's important that it be exactly right so if you don't think it's right come and see me because we need to change the spreadsheet somehow maybe a quiz that left out or government school or whatever you whatever it is right it should be self consistent with everything that's in the great book already when I construct this spreadsheet I go to the grade book by Paul :colon numbers out and I pasted into the Excel spreadsheets awards in the great book is what's in my spreadsheet OK any questions on that so in All-Stars I'm concerned this is exactly where we want to be going into the final exams
this is exactly the histogram and I was hoping we would have at the beginning of the quarter kilometres in here somewhere right you guys are looking like you doing really well by
barring some sort of cataclysmic breakdown right this GM could look a lot like this at the end of the quarter OK but that doesn't mean that there will be a
lot of flux going on inside the system ran their well-being there
always is but somebody can have a meltdown the reasons that might be out of their control you know and someone's just going to have a break
day and you know both those things are gonna happen OK so half of
the final exams beyond kinetics half of it is before problems 2 of them is going to be kinetics 1 of them steady state mechanisms gonna be but that's all we have time for before problems formal type heart problems so a spell that out next week and to tell you what those problems are going to be more or less like I always do president an excellent idea
but this has always been on the final exam enzyme
kinetics I dislike the subject I think if you understand enzyme kinetics you understand some very important basic chemical kinetics principle OK now I know most of using this before or how many have you seen enzyme kinetics good
all right the way you really learn
stuff by seeing it more than once right the 1st time you year that in mm and then doesn't go any further until the see again the 2nd time in its seats in a little further along Via eventually goes all the way to the core of your brain stem and you understand it at a very deeper level right now I'm still not at that point myself but you
need to see topics like this more than once and we'll take away something new maybe I'll say in a different way he'll take away something new even if you've seen it the OK
so we're going back to talking about you know molecular reactions you'll recall that I said that most molecular
reactions are of 2 types the reader decomposition reactions you got a reactant upon breaks the breaks into 2 particles or 3 particles right it that the decomposition reaction all its content configuration changes so undergoes my summarization write those the 2 most common types of you know molecular reactions the Bulls important we won understand how they occur
all right because it's unusual for you molecular reactions just
spontaneously happened because there's an activation energy that's required for most reactions right as an activation energy in an summarization reaction the eligibles 2 states might be the same because of an urgent energetic barrier between them system transfer example all right and the decomposition reaction usually a bond after bring that's a lot of energy OK so reactions
like this in general just don't happen all right ages
reacts to give products now if that was what with the work that way there wouldn't be any right there would already have it be gone right you have to take a concentrated into a container that some partial pressure so they can collide with itself and then this reaction happens but there has to be an energetic collisions somewhere so the
Langmuir Hinshelwood method gives us the most primitive way to think about this right this is
not the most advanced mechanism this is the most primitive you the molecular reaction mechanism what happens basically
8 hits collides with itself that's the the key that collision is going to
impart the energy necessary for this reaction and move forward over this energy barrier OK but after the
collision occurs that this that's the step right here why this activated a stock can collide with a again and get deactivated that's this step right here right so we
form a star by collision but it's a start undergoes a 2nd collision the energy can get transferred the energy
necessary for the reaction could be lost in the 2nd collision now it's a little
surprising maybe that that can happen you'd think the 2nd collision would make it even more energized and that could happen to all right we'll talk about the back happened to all right
but look what matters to us is that some fraction of these collisions are going to deactivate the a star it's going to go back to a and that the show's right here and finally the last thing that can happen is this a stock it's not
deactivated it can undergo exhuming the molecular reactions here I'm showing a
decomposition right but it can also be an isomerization could only be 1 B instead of to here OK so the key is that there's a star has enough energy to undergo this reaction and so we can apply the steady-state approximation because a star an intermediate
if there's an intermediate mechanism you can apply the steady-state approximation if there's no intermediate you can't applied steady state approximation right there has to be an intermediate and the mechanism in order for the steady-state approximation to make any sets what's at steady state it's the intermediate for goodness sake OK so because they
start as an intermediate we can apply it so we write an expression for the differential rate expression for a stock here the rate at which a stock builds up this reaction right here here's the rate at which it decays in this reaction right here in this reaction right here and then applying steady state approximation we just set that equal to
0 these are just differential rate expressions also for a and B. and that we can simplify this week moved all the negative terms on 1 side all the positive terms on the other side said them equal to 1 another and in sulfur a star up and then finally we applied the state start concentration into the cuts the rate expression for
products OK and so they start
steady is here and the scope of this whole thing and for that about 2 K 2 from here and this is just the expression I derived for the studies concentration of a stock and I'm done that's my
Lindeman Hinshelwood reaction
rate for the reaction to what is it predicted because these
predictions turn out to be very general 1 understand if I make a
big salt if I look at this expression of ideas look at it I can
already see there's going to be too limits to think about right how can handle I know that and by looking at it there's a plus
sign here but in the denominator there's an addition operations all right so immediately tells me that if this is huge compared to I can neglect that's an ominously 1 type of
kinetics conversely if this is huge compared to their these areas are going to cancel and it's a completely different kinetics but
the key is a look at the expression and I see the addition operation whether it's in the numerator or the denominator that tells me that there can be too limiting behaviors that are reported in the kinetics so the first one is
that them make a future I blow this term up until K 2 is
small in comparison
then this is going to cancel with a right here but and so you see I got rid of 1 of these days and all of these constants that are going to be rolled up into some effective rate constant and this thing is going to look like it's just a
first-order reaction in a it's gonna look like a first-order reaction that high pressure
or high concentrations of now what is this new mechanistic late well look if I make a big what that means is that this deactivation reaction here happens with
high-efficiency no words and creating this energized based on are alright but if there is a high partial pressure of a it's been a is going to be colliding into a star a star is not gonna live for very long and where they go back
toward the energized a B Indiana the
energized ation of a it's going to be very efficient if that's true
it's just like this forward reaction is in rapid equilibrium this is happening and this is happening right away and then this happens he generated a stop at a star reacts deactivated activation deactivation activation deactivation
it's happening rapidly OK so it's like the 1st step of the decree equilibrium we can think about an equilibrium constant for this forward reaction right here I would just be a star over a because the EIS canceled costs by
writing equilibrium constant expression OK so the rate of the
reaction there would be 2 times Kate 2 times a star right except that they start to the Big K times a day and so that's my reaction rate and had look at this that equilibrium constant Siegel the K-1 overcame minus 1
yes that's what you would expect it to OK so if that 1st reaction is happening rapidly in the forward reversed directions which it well at high pressure that's August the
first-order kinetics alright and there's 2 ways to think about it .period but basically the
deactivation process becomes very efficient what about the
smaller if I make a small industry goes away not just that K 2 and the denominator right it's going to be overall 2nd order and what is this mean mechanistic elite means basically I'm turning this off I'm turning off the back
reaction I make a star and at low pressures of a it's not going to get deactivated once it forms it's going to hang around until a reality so far there is no back reaction and under those conditions were the
second-order kinetics OK so this plot must not
be mysterious to you right if you look at the point you got it's only 1 slide and presentations that 85 slides I don't need to understand that what that particular block as it makes no sense you do need to understand 1 of my
plotting here this is logically effective Katie effective that the effective right there right so what we're doing is we're saying Look take this
Lindeman Hinshelwood rate expression that mess
right there alright and pretend that it has this fall all right take 1 of the EIS out because a
square the numerator and roll everything else out into K
effective right and that's the key effective them plotting here right
were pretending that the reaction is a first-order reaction so it's the 1st order rate constant for the Lindeman Hinshelwood and on this axis and
plotting the partial pressure of a actually the log Of the partial pressure there all right and
what we call a lot because we want conveyed the picture that were plotting a over a huge range of pressures right from very low very high that's why we were calling this a lot OK and so
what we want notice here is that there's 2 regimes to the first one is 1 where this is where we we've got a second-order kinetics OK it's OK effective as in the case K 1 times 2 times a day and I think you can see by planned this invocation affected get 2nd order reaction kinetics right I
get a squared right Sofia
the rate constant right K effective depends on a that's why we're seeing this when your behavior like this but when we go to high concentrations of a we get first-order kinetics OK so we have first-order kinetics assumed here already and so the rest of this is just a bunch of constants OK so what we should see it in the lab as we see the reaction
act like a second-order reaction and then as we increase the pressure increased the pressure increased the pressure rolls over and starts to act like a first-order reaction at the experimental behavior that we expect to see it's surprising that that level of complexity exists we're talking about a reaction that is a ghost of products .period that's the whole reaction all right but we still see this complex behavior we see the
apparent reaction rate change right the pair mechanism changes we
change the pressure of a even dull all that can happen is a reacts to give products but there still complexity to the behavior that we see in the lab even tho it's the world simplest reaction literally OK so
we get some more algebra we can take this little miniature would rate and here's that effective rate cuts and we were just talking about now I've written down what it is right here's what it is mathematically OK and then I can take 1 over that and I give to terms because his 2 terms in the denominator survived but these guys the the numerator I'm going to have to terms corresponding to these 2 guys there they are all right and then the normal way to diagnose whether land that
Lindeman Henschel would applies to the mechanism that you're talking
about is the plot this 1 overcame affected verses 1 over a you should get a straight line just looking at this mathematics you should get a straight line with slope of 1 over 2 K 1 and that should be the intercepts we should see a positive intercept here right and so qualitatively visible light is doing what we expected to right now there's there's a
breakdown that it is occurring here we have a talk about why that happens hopefully we'll get to that before the end of the class OK so now this looks a
lot like this I think you'll agree are right we've got a forward reaction reverse reaction Ford reaction a reverse reactions and then we got what looks like a you know molecular reactions step at the end here just like we do right here I feel this looks similar to their deaths and we already understand when miniature would pretty well so qualitatively
wouldn't expect that to do something similar we can apply the city-state approximation again we've been through this a million times but we're not going to talk specifically about this reaction but if you do the mathematics you find out that it behaves exactly the same way as the women Henschel would mechanisms all right and were denied zoom through
that and you can look back on the on the slides and work through those equations if you want to but basically what we want to do is we want
applied these mathematics now to this reaction this is the enzyme kinetics there were trying to
get into that and look at this
carefully write this looks like a miniature would this looks like the right forward reaction reverse reaction EU the molecular last step it's irreversible right this is the
classical enzyme kinetics mechanism so
this is the enzyme this is the reactant
we call it the substrate enzyme kinetics so 1 of the things that you should understand what enzyme kinetics is that it's been designed to confuse you and we haven't
called this the substrate before we call it the reactant right but now we're these are both reactants but what we call reacted when it shows up as a product a catalyst for
God's sake right so by
golly that's a catalyst all right it's gonna react with asked to form an enzyme substrate complex when the reaction occurs in this enzyme substrate complex and then the product is released and the enzyme is regenerated at the end of the process all right that's the
we don't call this guy product because he started out here are so he's a catalyst that's what the role
of the enzyme is to do the enzyme is a very efficient biological catalyst right it is this enormous laying in in most cases it's the giant molecule with the molecular weight of 100 thousand right and so it's got this really intricate architecture right in its job is to reduce the activation energy of the reaction which you can do in any of several ways hopefully will be seeing more about that
so the matically here's the cartoons if you Google
enzyme kinetics and you look at images you see a lot of cartoons that look like that right here the
enzyme this estimated relative size right the enzyme
is this thing that's 100 thousand molecular weight the substrate can be a tiny molecules like ethanol water right right to be a small biological molecule molecular weight 50 OK so it's it's
not comparable in size to this but we're drawing here right it's tiny in dots in the enzyme the enzyme in general
recognizes the substrate molecule in buying said right is not any substrate molecule that swimming around and they're not rate even a chemically similar wines will not blind to the enzyme the enzyme has now thank you yes specificity OK
so here's his binding process this is the so-called active site of the enzyme it's this cartoon is meant to convey the idea that it's
recognizing this green substrate molecule now chemistry happens right a bond between these 2 things broken perhaps right and the 2 products get spit out in the enzyme is regenerated that's the picture but that's the picture that we
want understand OK so in
5 minutes we're going to snap through some slides and we're going to look at how these kinetics work and then we're gonna come back and do it again on Monday so that we were all clear on this because this is important here's our
kinetics scheme all right if we look at the differential rate offer the product I think everyone will agree that it's OK to times the concentration of this enzyme substrate complex OK
nothing surprising about that we're going to apply the steady-state approximation when we do that we got the rate at which the enzyme substrate complex builds up blooms we got the rate at which case bloom with at the rate at which a reacts right here is here is that the reaction rate that back right there here's that forward rate there all right this depletes the enzyme substrate complex this depletes the enzyme substrate complex Eliza and those are minor signs and this builds up the enzyme substrate complex but the plus sign
so it's just the standard steady-state approximation COM port the steady-state approximation is his see how applying it indiscriminately without thinking about what the rates of various whole whole babies rate constants are as we know darn good welds the steady-state approximation doesn't always work were not paying any attention to that are OK
no it's hard to know what the enzyme concentration is because it's changing 1
because the enzyme reacts to form the influence and enzyme substrate complex OK so we don't know a priority would be free
enzyme concentration it is but we do with all the total enzyme concentration because we put the enzyme in the stupid beaker so we know if there's 1 thing we know it's how much enzyme we put into the bigger total enzymes that's the 0 right that's the
amount we put in the beaker anything can have 2 forms that could be free and sirens and substrate complex there's no other options for the
enzyme In the simplest picture will talk about complexities later right so the enzyme can be in 2 states free fall bound by substrate so now we
can express the enzyme concentration as the difference right before the tall and then concentration the amount of it that's about as the substrate bound to the substrate OK so that I can just plug that in 3 enzymes I just applied that expression and for year Bo OK and then when I distribute that across the sky was for different terms 3 of the negative and 1 of them positive and then I'm just moving a positive term over some putting all the negative ones on 1 side positive on the other side and then by consulting for the enzyme substrate complex there right there is the expression that get just sulfur EDS this expression right here in terms of to be pretty easy to do right don't
forget that we're talking about the steady-state enzyme substrate complex concentration right it's not any it's not this is not a totally general expression it applies to the steady approximation OK show
earlier we said this is the rate of the reaction right this is the rate that last step and sense of 3 complex and skate to so now I can just plug that in for that but that's the rate of the reaction but
and finally we're going to divide the numerator and denominator balls like
the 1 right when I do that I
lose K 1 here right under loose K 1 here and put K 1 under these guys boom areas now he's gone from there and he's gone from there and the Michaelis-Menten equation the most
important equation in enzyme kinetics To we just arrived it's pretty easy very
Mass here Is called Michaelis constant we'll have
more to say about that on Monday what worries that Fuerman
Computer animation


Formal Metadata

Title Lecture 24. Enzymes
Subtitle Pt. I
Alternative Title Lecture 24. Lindemann-Hinshelwood Part II
Title of Series Chemistry 131C: Thermodynamics and Chemical Dynamics
Part Number 24
Number of Parts 27
Author Penner, Reginald
License CC Attribution - ShareAlike 3.0 Unported:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal and non-commercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this license.
DOI 10.5446/18965
Publisher University of California Irvine (UCI)
Release Date 2012
Language English

Content Metadata

Subject Area Chemistry
Abstract UCI Chem 131C Thermodynamics and Chemical Dynamics (Spring 2012) Lec 24. Thermodynamics and Chemical Dynamics - Lindemann-Hinshelwood Part II - Instructor: Reginald Penner, Ph.D. Description: In Chemistry 131C, students will study how to calculate macroscopic chemical properties of systems. This course will build on the microscopic understanding (Chemical Physics) to reinforce and expand your understanding of the basic thermo-chemistry concepts from General Chemistry (Physical Chemistry.) We then go on to study how chemical reaction rates are measured and calculated from molecular properties. Topics covered include: Energy, entropy, and the thermodynamic potentials; Chemical equilibrium; and Chemical kinetics. Index of Topics: 0:00:06 Enzymes 0:07:58 Most Elementary Reactions are Unimolecular or Bimolecular 0:09:45 The Lindmann-Hinshelwood Mechanism 0:16:53 The Kinetics of Pressure-Dependent Reactions 0:22:34 The Michaelis-Menten Equation

Related Material



  544 ms - page object


AV-Portal 3.7.0 (943df4b4639bec127ddc6b93adb0c7d8d995f77c)