James McEvoy

James McEvoy

I teach and research biological chemistry in the Department of Biological Sciences at Royal Holloway, University of London. Before that I taught in Denver, Colorado, and studied at Oxford and Yale.

Location UK

Activity

  • James McEvoy made a comment

    Folks, thank you for being with us over the last few weeks. I'm signing off this run, so until the next time, keep on enjoying your learning. It's been a pleasure.

  • @JoyceJ In your scenario, the amount of water produced is limited by how much hydrogen you start with. If you remove that limitation (by imagining, for instance, that you start with 2 mol H atoms and 1 mol O atoms) then the amount of water produced is limited by the position of equilibrium, and my statement holds. (BTW this question is certainly not dense and...

  • Welcome @ParbhjotK !

  • Reactions with very large equilibrium constants, like this one, are "irreversible": in other words, the products (water) are so much more stable than the reactants (hydrogen and oxygen) that they predominate by many orders of magnitude in the reaction mixture.

  • Sorry this wasn't working for you, @JoyceJ

  • It's a contentious issue, but some researchers are more optimistic than the BBC (see here, for instance https://www.pnas.org/doi/10.1073/pnas.1920877117).

  • Well, one day... if the rate of fixation had been able to keep up with combustion then the atmosphere wouldn't be accumulating CO2, of course.

  • Welcome @JoyceJ !

  • Researchers are still learning about the semidwarf varieties. Some of the most interesting recent molecular results are described here https://www.cell.com/action/showPdf?pii=S1674-2052%2821%2900002-2

  • Almost all of the carbon in plants (in cellulose, lignin, proteins etc) comes from the air, not from the soil. There's a recent paper on the subject here: https://pubs.acs.org/doi/10.1021/acs.est.8b06089

  • Well done @AnnaSeggons, that's about what I got too!

  • Yes, "elevated CO2" does refer to increased levels in the atmosphere. Other things being equal (which they may not be), more CO2 should improve the efficiency of rubisco.

  • @ChrisG Done! But I'm not going anywhere for a while, to make up for missing so many of the early comments on this course run.

  • Thanks @AnnaSeggons , glad you enjoyed it!

  • Yes i'ts histidine, well done @ChrisG . The shape is rather complicated, you are right.

  • Welcome @AnnaBeach, glad to have you on the course.

  • You've hit on a rather sore point in evolutionary philosophy. To what extent should we ascribe a specific purpose to an evolved structure? It's hard to teach or learn about biology without doing so, but it ain't necessarily so.

  • @ChrisG Yes, so when an electron joins a bonding molecular orbital it experiences, on average, a greater positive charge than it did in the atomic orbital.

  • Right. Ethanol is metabolised oxidatively, generating NADH. Unfortunately the metabolic products must be processed by using ATP, so ethanol is not a good source of energy overall.

  • Great find, @ChrisG. It is true that fermentation can occur in the presence of oxygen under certain conditions, but generally cells use available oxygen to respire aerobically.

  • Great question @ChrisG . The answer is that the cell's objective is not only to create a potential gradient. The individual ion concentration gradients are also important and are used for different purposes, for instance in neurons to propagate action potentials.

  • @AnnaSeggons perfect!

  • Yes, some energy is certainly dissipated - but not all of it. Some is indeed converted into useful work.

  • As for other effects on body size, yes, it might not all be good news!

  • You are right @ChrisG , brain development is not the same as activity - although a more developed brain is implied to be more metabolically active in this study.

  • @ChrisG by letting the lid move up you are indeed allowing the gas to do work, decreasing the internal energy of the system.

  • The published value of the enthalpy change is 222 J / g, but with such a simple experiment you're not too far off!

  • @CrisM no, the units of entropy change are indeed J / K / mol.

  • Exactly - the closer they are to a positive charge the more stabilised they are.

  • That's what she needs to get through the day @ChrisG . The smaller figure is her baseline metabolic requirement, the rest for physical activity.

  • Welcome everyone! I'm looking forward to discussing the course with you.

  • James McEvoy replied to [Learner left FutureLearn]

    Thank you for your company and your thoughtful contributions @MicheleCampanelli

  • Just the one, actually - NADH donates a pair of electrons to reduce the carbonyl group to an alcohol.

  • Good question! Your finger did gain some kinetic energy as it moved - and some gravitational potential energy, too, because it moved upwards.

  • Ah, I understand now. I think it's the font that FutureLearn uses...

  • I'm glad you're enjoying the course, @AdamNDIFOR .Thank you for the feedback.

  • I agree Ken, it would be a game changer if it could be made to work.

  • Thanks for your contributions, @JohnSloman

  • Thanks for your company and the feedback, Ken.

  • Right on both counts!

  • Well, when you factor in transport then it may well not.