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MCAT
Unit 5: Lesson 12
Overview of metabolism- Overview of metabolism questions
- Overview of metabolism: Anabolism and catabolism
- ATP: Adenosine triphosphate
- ATP hydrolysis: Gibbs free energy
- ATP hydrolysis: Transfer of a phosphate group
- Oxidation and reduction review from biological point-of-view
- Oxidation and reduction in metabolism
- Electron carrier molecules
- ATP hydrolysis mechanism
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ATP hydrolysis mechanism
Created by Sal Khan.
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Why does the oxygen in water give its pair of electrons to the phosphate in the first place. Likewise, why do the electrons go to the oxygen when the phosphate cannot "handle" them. Can someone please explain the process to me. I tried to re watch this video twice but I couldn't get it.(42 votes)
the phosphate group (like most molecules) does not want to remain positive so it takes some electrons from the H2O to become more negative while breaking off of the ATP molecule (which releases energy), if the water was not there than it would have to deal with being positive.(4 votes)
I can't understand how energy is released from ATP. I mean does energy behave like a product? What do you mean by "energy released"?(6 votes)
In the case of simple hydrolysis, the energy would be released as heat, which means giving the molecules additional speed. You could view it as the negative charge of the three phosphate groups of ATP repelling on another, so when one group is removed, the ATP and Pi repel one another, so have a greater speed than before.
In most cases however, the energy released from ATP hydrolysis will be used to drive a second reaction. Here the energy is more abstract but involves using the change in shape and charge on ATP to change an enzyme shape and forcing another molecule into a different shape so it can undergo a chemical reaction more easily.(8 votes)
What are the particular determining factors that decide what types of energy are released by ATP when placed in water with the proper charge?(3 votes)
Sal, at33:51, what is a lone pair of electrons?(2 votes)
In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom and is sometimes called a non-bonding pair. Lone pairs are found in the outermost electron shell of atoms. They can be identified by using a Lewis structure.(3 votes)
How much energy is released by ATP in jk/mol ?(2 votes)
How does the oxygen on the middle phosphate hold two extra electrons and still bond to the phosphorus?(2 votes)
In this compound, the Oxygen would give both the electrons in the bond instead of one .(1 vote)
How exactly is the energy released? How does the formation of the bond between the P and the O and the breaking of the bond between the P and the other O release energy? Why do the electrons become more comfortable after this is complete?(2 votes)
This reaction is exothermic, meaning energy is being released to the system once those bonds break up. I heard somewhere here that about 65% of the energy is indeed being wasted in the form of heat, and only about 35% of the transition from ATP to ADP is usable by the cell as either kinetic energy or otherwise (perhaps electrical energy in certain cells, such as nerve cells who transmits pulses, though these usually happens due to potassium and sodium gradients)... :)(1 vote)
- At0:58, what does Sal mean by "the two pairs of oxygen that aren't in bonds" and "in their outermost shell"?(2 votes)
- He left out an important word. He should have said that the oxygen has "two lone pairs".
If have not studied enough chemistry to understand lone pairs, then you probably should review that material.
In brief though, a lone pair is a pair of electron in the same orbital in the valence shell of an atom. As such, lone pairs do not readily bond. In compounds, oxygen has two lone pairs, so it has two sets of electron pairs that don't readily engage in bonding. Thus, its valence shell has only two orbitals that are readily capable of bonding.
When a atom with lone pairs bonds, the bonds will move away from the lone pairs as much as possible. This is why water is a bent molecule, the two bonds are bending to be as far from the lone pairs as they can get.
"Lone pair" is actually an older term. In modern usage the term "nonbonding electron pair" is preferred. However, most textbooks still use "lone pair".(1 vote)
- what do those dots around the oxygen in water molecule at1:00depict ?(1 vote)
After hydrolysis, how can hydrogen proton form a bond with oxygen if it's just a proton, there's no electron to share(1 vote)- Proton is hydrogen ion - hydrogen atom stripped of electron. It can bond with any atom/molecule/ion which does have electron and share that one. Of course it would bond more readily some kind of negative ion than atom.(2 votes)
33:51Video transcript
Sal: In the previous video we
talked about how an ATP molecule can, in the presence of water,
hydrolysis will take place, and one of the phosphoryl
groups could be plunked off, and how that would release
energy because these electrons are going to be able to go
into a lower energy state. You could imagine that this
was already not that stable of a bond, that all these
negative charges wanted to get away from each other, and
once this is plunked off, then of course when they get into a more comfortable state energy is released. But you might say, "I want
more. I want to actually see "the mechanism by which the
hydrolysis takes place." That's what I'm going to do in this video. Let's start with our ATP molecule, and let's throw some water in there, H2O. Let's say this is water right here, oxygen with two hydrogens. I'll do the two pairs
of oxygen that aren't in bonds right over here,
in the outermost shell. Actually let me draw one more
water molecule right over here. There's multiple way that you could actually depict this right over here. Let's say that one of these, let's say this water molecule right here, and obviously no chemical
reaction happens this cleanly. This is showing how it
could happen if they just bump into each other
in the exact right way. This has got this pair of electrons. Let's say this pair of
electrons is essentially given by this oxygen to
this hydrogen proton. We could draw it like this right there. It nabs just the hydrogen, then
both of these electrons that are in this pair, that are
in this bond I should say, go back to the oxygen to form,
essentially you could think of this as a pair of electrons
attached to that oxygen. Then that gives the oxygen
license to allow these two electrons to form a
bond with the phosphorous. The phosphorous isn't in
the mood to form six bonds, it's already got five, and this is a fairly uncomfortable situation for it. That allows these two electrons
right over here to go, these two electrons to go to
this oxygen, just like that. As a result of everything
I've just depicted happening, what does it look like? Let me draw a little arrow here. Now you're going to have
your adenosine diphosphate. Let me put it over here. And just to be clear,
this thing has now gained, this oxygen right over here,
one way you can think about it, it was party to a bond so it
was sharing two electrons. Now it's getting both of the electrons, so now it's going to
have a negative charge. It had half of-- Actually it
had a little bit more than half, it's more electronegative
than the phosphorous. Now it's going to get both of them. Now this is going to
have a negative charge. This is the adenosine diphosphate. This phosphoryl group over
here, let me just redraw it. It's going to look like this. Double bond to that oxygen. You have this oxygen right
over here. That's there. You have that oxygen right over there. And of course the water, the
water molecule, or I guess now it's just going to be
an OH group, is going to be, it has ... Let me see if I can
make the colors interesting. These two electrons have now
formed a bond and you have the oxygen and of course
this hydrogen here. I haven't draw in any other oxygens but this thing still has two lone pairs. And of course you have this character right over here, who gained a proton. This one you can depict like this. It's oxygen, hydrogen, hydrogen. It had one lone pair, but now it gave half of this lone pair to form
a bond with that hydrogen, and hydrogen without an
electron is just a proton. Actually let me draw it like
this just so you can see it. These two are now the
two electrons in this bond with this, with this hydrogen proton. This right over here, this
is a positively charged, this is a positively charged
molecule right over here. And you can imagine
maybe this thing breaks off and it could be viewed as a proton, or you could view this as a
positive charged molecule, but either way this is the
reaction that we just depicted. You have ATP being,
hydrolysis takes place. You're left with ADP, you're
left with a phosphate, a released phosphate molecule, and then you're left
with a positive charge. You could either view this
as kind of a proton or the proton attaches and forms a
hydronium ion right over here. And of course in the process
of doing all of this, as these electrons got
into a more comfortable situation just sitting
right over here and allowing this thing to break
off, it releases energy. It releases, it releases energy,
which is in most biological systems the whole point of
having the ATP molecules around.