Bio question

[Erhatstil]

---

Members do not see this ad.

In a redox reaction..

A. the oxidizing agent donates electrons
B. the reducing agent accepts electrons
C. the reducing agent is most electronegative
D. the substance that is oxidized loses energy
E. the substance that is reduced loses energy

answer is.........D

how do we equate electron loss to energy loss?

 

[dentalWorks]

In a redox reaction..

A. the oxidizing agent donates electrons
B. the reducing agent accepts electrons
C. the reducing agent is most electronegative
D. the substance that is oxidized loses energy
E. the substance that is reduced loses energy

answer is.........D

how do we equate electron loss to energy loss?

of course its D. When you studied glycolysis, remember how they always referred to the process as "the oxidation of glucose".... what does this "oxidation" mean? It means the cells are pulling the electrons from the glucose

To make life easier for you, when your thinking about biochemistry and energy, relate the term "electrons" = "energy".... So when you oxidize glucose, your making it loose its electrons (loosing energy)

Now here are some terminology for you:
Oxidation = pulling electrons off (for example, if molecule_A is being oxidized, its LOOSING electrons)

reduction = putting electrons on (for example, if molecule_B is being reduced, its gaining electrons)

Agent = "acting upon" (for example, molecule_C is an oxidizing agent, meaning its ACTING on a near by molecule and making this near by molecule loose its electrons, so therefore molecule_C is being REDUCED)

 

[Erhatstil]

dentalworks, thanks for the response. but its not the redox reaction and its constituents i dont know understand. in terms of glycolysis, is it fair to say, hypothetically, that if two separate glucose molecules are about to enter glycolysis, but 1 of the molecules has less e-, then this molecule as it goes thru glycolysis and krebs won't pass as many e- to NAD+ and FAD, and thus less ATP will be produced (compared to the glucose molecule that hasn't lost any)? if so it make sense.

maybe this is too objective but, Ca---->Ca2+ doesn't necessarily represent a loss of energy does it? maybe i need to be more creative in my thinking, but this question seems a little ambiguous.

or maybe i should get out the biochem book and figure out how this works

thanks for your help man, much appreciated

 

[dentalWorks]

dentalworks, thanks for the response. but its not the redox reaction and its constituents i dont know understand. in terms of glycolysis, is it fair to say, hypothetically, that if two separate glucose molecules are about to enter glycolysis, but 1 of the molecules has less e-, then this molecule as it goes thru glycolysis and krebs won't pass as many e- to NAD+ and FAD, and thus less ATP will be produced (compared to the glucose molecule that hasn't lost any)? if so it make sense.

I am not exactly understanding your question here, are you saying that one of the glucose is donating "less electrons" than the other? Glycolysis (in general) is a finite system, it takes glucose and converts it into 2 pyruvates. There is no less/more e-'s from a glucose molecule

maybe this is too objective but, Ca---->Ca2+ doesn't necessarily represent a loss of energy does it? maybe i need to be more creative in my thinking, but this question seems a little ambiguous.

your right, Ca --> Ca2+ is not referring to energy gain / lose. What I was trying to say is that when your SPECIFICALLY talking about energies and biochemistry, your going to encounter a lot of NAD(H)'s, FAD(H)'s, NADP(H)'s and such, and by convention, the difference between say NAD vs NADH is that NADH is a "high energy molecule" cause its carrying 2 electrons. When it drops off those 2 electrons, its back to its oxidized form (the NAD+)

[/QUOTE]

 

[Erhatstil]

sorry bad example, i'm just trying to a paint a picture so u can see what i'm asking. as glucose is oxidized during glycolysis, how is this a loss of energy? i know NADH and FADH2 are considered "high energy" but isn't energy absorbed as the bonds break with their H+'s during ETC? i'm thinking along the lines of since NADH--->NAD+ is endothermic, wouldn't NADH have to partake in an exothermic reaction and release energy, to be considered "high energy"?

which sort of gets me back to thinking oxidation isn't losing energy

 

[dentalWorks]

sorry bad example, i'm just trying to a paint a picture so u can see what i'm asking. as glucose is oxidized during glycolysis, how is this a loss of energy? i know NADH and FADH2 are considered "high energy" but isn't energy absorbed as the bonds break with their H+'s during ETC? i'm thinking along the lines of since NADH--->NAD+ is endothermic, wouldn't NADH have to partake in an exothermic reaction and release energy, to be considered "high energy"?

which sort of gets me back to thinking oxidation isn't losing energy

Ahhh I see what your asking now... You don't see why the oxidation of glucose is "losing" energy

Before I talk more, lets get a few things settled, without going too deep into the actual physical chemistry calculations of why the glucose that gets oxidized actually looses energy...

NAD+ molecule holds less energy than NADH.. This figure explains what I mean. Going from NADH --> NAD+ is an exothermic process (-160 KJ)... so the only way your going to make NADH from NAD+ is by adding "energy" correct?

When you study glycolysis, one of the fundamental things you'll see is that 2 NADH's are produced for every 1 molecule of glucose. Now why is this called "oxidation"? Because the electron that come from the glucose are in the form of a Hydride ion (:H-), your sucking up 2 hydrides from each glucose molecule and each hydride is reducing one of the NAD+'s -----into-----> NADH's

Step 3 in this video really shows how the Hydrides are being transfered from the "glucose" to the NAD+'s
http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html


I think you get it now. Basically the production of NADH's is an energy requiring step, and in the same time, the way you reduce NAD+ is by adding 2 electrons to it (from hydride ion).... those electrons are coming from the original glucose molecule (hence your oxidizing glucose to make NADH's)

 

[Erhatstil]

okay makes sense. one last question, what makes NADH-->NAD+ exothermic? if we're breaking a bond we should be absorbing energy as its generally an endothermic process right?

thanks again

 

[dentalWorks]

okay makes sense. one last question, what makes NADH-->NAD+ exothermic? if we're breaking a bond we should be absorbing energy as its generally an endothermic process right?

thanks again

whoaaa, not any bond-breakage is an endothermic process. Why do we stick gasoline in your cars? we are breaking the hydrocarbon bonds in gasoline and its liberating alot of energy to run our motors...... I mean to INITIATE the process you need a little energy (activation energy ~ i.e spark plugs in your engine)

I don't have my biochemistry book next to me, but if you have a electron potential table laying around, NAD+/NADH pairs are always found in those tables, you'll see why NADH to NAD+ is an exothermic/spontaneous process

 

[Erhatstil]

here's a chart i found for the reaction: CH3CH2OH(g) + 3O2(g) ® 2CO2(g) + 3H2O(g)

http://www.avogadro.co.uk/h_and_s/bondenthalpy/bondenthalpy.htm

Bond breaking:
Total endothermic value = (+347 x 1) + (+413 x 5) + (+358 x 1) + (+464 x 1) + (+498 x 3) = +4728 kJ
Bond making:
Total exothermic value = (-464 x 6) + (-805 x 4) = -6004 kJ​

so individually, each bond breakage is an endothermic process. but overall the process is exothermic because the total bond formation energy is much more negative than the positive energies of the bond breakages. somehow, this must be happening with NADH-->NAD+. maybe the new bond that H+ eventually makes somewhere is very exothermic. being 160kj/mole more negative than the bond breakage. see why this whole thing is kind of confusing?

one of the fundamental concepts i remember from biochem, and its been a few years, was that bond breakage is generally endothermic, and bond formation exothermic.

 

[Impulse155]

In a redox reaction..

A. the oxidizing agent donates electrons
B. the reducing agent accepts electrons
C. the reducing agent is most electronegative
D. the substance that is oxidized loses energy
E. the substance that is reduced loses energy

answer is.........D

how do we equate electron loss to energy loss?

If your still unclear think of it like this
For A, B remember LEO GER
Lose Electrons Oxidation
Gain Electrons Reduction

The oxidizing agent is the thing causing something else to be oxidized. (therefor getting reduced)
The reducing agent is the one causing something else to be reduced
(therefore getting oxidized)


A) Due to what was just said "the oxidizing agent donates electrons" is wrong. The oxidizing agent is being reduced, therefore gaining electrons.

B) "the reducing agent accepts electrons" is wrong. The Reducing agent is being oxidized, therefore gaining electrons.

C) Remember the most electronegative element is Flourine. Flourine always wants to gain electrons to try and make it a full valence shell. Therefore flourine is going to want to be reduced. Or the oxidizing agent.


D) Correct answer. Something that loses electrons is losing energy. If its losing valence electrons it loses energy.


E) The substance that is reduced loses energy. If the substance is being reduced then it is gaining electrons. Therefore it would be gaining more energy. As you fill a valence shell it gains energy.

Anotherway you could have done this is just look at D and E.
How can the substance loseing electrons gain energy. And thent he following statement be the substance gaining electrons loses energy. Therefore one must be wrong, one must be right.


Edit:
I looked at where you said breaking bonds is endothermic. Just want to verify what dentalworks said. That is not true. Think about it. How is it that breaking something will cause you to store energy in it. That means forming a bond would release energy. Making something takes energy. Therefore causing making bonds to be endo, breaking exo.

 

[dentalWorks]

so individually, each bond breakage is an endothermic process. but overall the process is exothermic because the total bond formation energy is much more negative than the positive energies of the bond breakages. somehow, this must be happening with NADH-->NAD+. maybe the new bond that H+ eventually makes somewhere is very exothermic. being 160kj/mole more negative than the bond breakage. see why this whole thing is kind of confusing?

Thats exactly correct, when you break a bond you have to give it "energy" to break, and when you form a bond, energy is release. However when studying biochemical processes, individual bond breaks/formations are not as important as studying the WHOLE system. The energy that is used to convert NAD+ to NADH isn't exact energy like the one you study in a typical general chemistry reaction, this internal energy came from the initial priming steps of ATP into the glucose molecule early on during the glycolysis that lead to having it split into two 3-carbon molecules....

for the time being, fuels entering the organism (say in the form of gluclose) are high energy compounds, meaning they have high energy electrons..... You can't liberate these electrons ALL in the same time cause the cell would explode from the amount of heat liberated, you have to do it in slow and gradual steps.... meaning your pulling off those high energy electrons 1-to-few steps at a time.

The whole reason why non-autotrophs (like us) eat glucose is to provide our systems with high energy molecules (glucose) which have high energy electrons.... we oxidize these fuels (pulling their high energy electrons) so we can survive

 

[Erhatstil]

If your still unclear think of it like this
For A, B remember LEO GER
Lose Electrons Oxidation
Gain Electrons Reduction

The oxidizing agent is the thing causing something else to be oxidized. (therefor getting reduced)
The reducing agent is the one causing something else to be reduced
(therefore getting oxidized)


A) Due to what was just said "the oxidizing agent donates electrons" is wrong. The oxidizing agent is being reduced, therefore gaining electrons.

B) "the reducing agent accepts electrons" is wrong. The Reducing agent is being oxidized, therefore gaining electrons.

C) Remember the most electronegative element is Flourine. Flourine always wants to gain electrons to try and make it a full valence shell. Therefore flourine is going to want to be reduced. Or the oxidizing agent.


D) Correct answer. Something that loses electrons is losing energy. If its losing valence electrons it loses energy.


E) The substance that is reduced loses energy. If the substance is being reduced then it is gaining electrons. Therefore it would be gaining more energy. As you fill a valence shell it gains energy.

Anotherway you could have done this is just look at D and E.
How can the substance loseing electrons gain energy. And thent he following statement be the substance gaining electrons loses energy. Therefore one must be wrong, one must be right.

i know what you mean. its either D or E, but as you can tell by the discussion it hasn't been all the clear to me why this is true. for me to just accept the fact that "losing e-=losing energy" doesn't help me rest easy. i need to know why haha

Edit:
I looked at where you said breaking bonds is endothermic. Just want to verify what dentalworks said. That is not true. Think about it. How is it that breaking something will cause you to store energy in it. That means forming a bond would release energy. Making something takes energy. Therefore causing making bonds to be endo, breaking exo.

it is true that breaking bonds is endothermic, but the entire reaction needs to be considered to get an overall positive or negative change in energy.

 

[Erhatstil]

Thats exactly correct, when you break a bond you have to give it "energy" to break, and when you form a bond, energy is release. However when studying biochemical processes, individual bond breaks/formations are not as important as studying the WHOLE system. The energy that is used to convert NAD+ to NADH isn't exact energy like the one you study in a typical general chemistry reaction, this internal energy came from the initial priming steps of ATP into the glucose molecule early on during the glycolysis that lead to having it split into two 3-carbon molecules....

for the time being, fuels entering the organism (say in the form of gluclose) are high energy compounds, meaning they have high energy electrons..... You can't liberate these electrons ALL in the same time cause the cell would explode from the amount of heat liberated, you have to do it in slow and gradual steps.... meaning your pulling off those high energy electrons 1-to-few steps at a time.

The whole reason why non-autotrophs (like us) eat glucose is to provide our systems with high energy molecules (glucose) which have high energy electrons.... we oxidize these fuels (pulling their high energy electrons) so we can survive

thanks for taking the time to help, i'll def keep this mind.

 

[UCB05]

so individually, each bond breakage is an endothermic process. but overall the process is exothermic because the total bond formation energy is much more negative than the positive energies of the bond breakages. somehow, this must be happening with NADH-->NAD+. maybe the new bond that H+ eventually makes somewhere is very exothermic. being 160kj/mole more negative than the bond breakage. see why this whole thing is kind of confusing?

The process of NADH oxidation to NAD+ and H+ is not the same as HCl > H+ + Cl-. What happens to H+ after oxidation is irrelevant. Look at the structures of NADH and NAD+ in dentalwork's pic. In the process of losing that proton, the bonds actually get rearranged. NADH is not aromatic, whereas NAD+ is. The loss of the two electrons and H+ translates to a loss of electrochemical potential energy in the form of reducing potential. Breaking that H+ may be endergonic, but NAD+ has lower energy overall.

When dealing with smaller oxidations, just remember that a loss of electrons (oxidation) represents a loss of reducing potential and make note that it will have lower energy. Usually this comes in the form of loss of valence electrons or achievement of a full outer shell.