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
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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.
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James McEvoy replied to Joyce J
@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...
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Welcome @ParbhjotK !
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James McEvoy replied to Joyce J
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.
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James McEvoy replied to Joyce J
Sorry this wasn't working for you, @JoyceJ
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James McEvoy replied to Chris G
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).
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James McEvoy replied to Chris G
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.
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Welcome @JoyceJ !
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James McEvoy replied to Chris G
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
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James McEvoy replied to Chris G
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
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Welcome @EleanorHumphries !
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James McEvoy replied to Anna Seggons
Well done @AnnaSeggons, that's about what I got too!
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James McEvoy replied to Chris G
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.
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James McEvoy replied to Chris G
@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.
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James McEvoy replied to Anna Seggons
Thanks @AnnaSeggons , glad you enjoyed it!
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Yes i'ts histidine, well done @ChrisG . The shape is rather complicated, you are right.
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Welcome @AnnaBeach, glad to have you on the course.
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James McEvoy replied to Chris G
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.
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James McEvoy replied to Chris G
@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.
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James McEvoy replied to Chris G
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.
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James McEvoy replied to Chris G
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.
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James McEvoy replied to Chris G
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.
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James McEvoy replied to Anna Seggons
@AnnaSeggons perfect!
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Yes, some energy is certainly dissipated - but not all of it. Some is indeed converted into useful work.
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James McEvoy replied to Chris G
As for other effects on body size, yes, it might not all be good news!
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James McEvoy replied to Chris G
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.
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James McEvoy replied to Cris M
@ChrisG by letting the lid move up you are indeed allowing the gas to do work, decreasing the internal energy of the system.
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James McEvoy replied to Chris G
The published value of the enthalpy change is 222 J / g, but with such a simple experiment you're not too far off!
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James McEvoy replied to Cris M
@CrisM no, the units of entropy change are indeed J / K / mol.
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James McEvoy replied to Chris G
Exactly - the closer they are to a positive charge the more stabilised they are.
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James McEvoy replied to Chris G
That's what she needs to get through the day @ChrisG . The smaller figure is her baseline metabolic requirement, the rest for physical activity.
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James McEvoy made a comment
Welcome everyone! I'm looking forward to discussing the course with you.
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James McEvoy replied to [Learner left FutureLearn]
Thank you for your company and your thoughtful contributions @MicheleCampanelli
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James McEvoy replied to Anna Lodge
Just the one, actually - NADH donates a pair of electrons to reduce the carbonyl group to an alcohol.
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James McEvoy replied to Rosalind M
Good question! Your finger did gain some kinetic energy as it moved - and some gravitational potential energy, too, because it moved upwards.
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James McEvoy replied to Rosalind M
Ah, I understand now. I think it's the font that FutureLearn uses...
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James McEvoy replied to Adam NDIFOR
I'm glad you're enjoying the course, @AdamNDIFOR .Thank you for the feedback.
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James McEvoy replied to Ken Evans
I agree Ken, it would be a game changer if it could be made to work.
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James McEvoy replied to John Sloman
Thanks for your contributions, @JohnSloman
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James McEvoy replied to Ken Evans
Thanks for your company and the feedback, Ken.
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Right on both counts!
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Well, when you factor in transport then it may well not.
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James McEvoy replied to John Sloman
Odd, it works for me
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James McEvoy replied to John Sloman
There's a difference between energy efficiency and temperature difference. Energy is sometimes measured in British Thermal Units in this context (see here for example https://www.greenbuildingadvisor.com/question/calculating-furnace-efficiency)
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Thanks for the question. Engineers struggle to get the jet power they need from electric motors. The alternative might indeed be a net-zero emission, high energy density alternative to a fossil fuel.
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James McEvoy replied to Ken Evans
Absolutely true!
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James McEvoy replied to Marie G
Thank you for your company!
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James McEvoy replied to Marie G
Thanks @MarieG for putting the issue so clearly.
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The biggest generators of biomass energy in the UK are power plants which burn compressed wood pellets. Much of the wood comes from renewable forests in Canada.
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Great question. The answer is that "viability" shifts with the price of oil. If fossil fuels see a price hike then cellulosic biofuels become an option.
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James McEvoy replied to Ken Evans
Thanks for your contributions, @KenEvans
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James McEvoy replied to John Sloman
I imagine that this surge in energy usage coincided with rapid improvements in living standards. Other things being equal, greater prosperity in that period meant more energy use. Nowadays the two are decoupling in developed countries.
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James McEvoy replied to Ken Evans
Agreed. You might be interested in Bill Gates' recent book "How to Avoid a Climate Disaster" - it details some of these mitigating technologies.
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James McEvoy replied to Marie G
@MarieG The newer varieties covert nutrients into seed mass more efficiently. Older varieties need more nutrients to produce the same yield. All other things being equal, that means more fertilizer.
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James McEvoy replied to Ken Evans
Fascinating! Thanks for sharing that, @KenEvans
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James McEvoy replied to Rosalind M
Hmm can you give me the context, @RosalindM ?
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James McEvoy replied to Marie G
But the old varieties would have needed even more fertilizer, @MarieG , and would have needed much more land (with the corresponding environmental degradation) to feed the same number of people.
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James McEvoy replied to John Sloman
Thanks @JohnSloman, and for pointing out this mistake. The automatic transcription system struggles sometimes with technical terms.
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James McEvoy replied to Maria Grigg
Thank you for that, @MariaGrigg
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Welcome @HagerAbdo !
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James McEvoy replied to [Learner left FutureLearn]
Thank you @MicheleCampanelli for that interesting insight.
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James McEvoy replied to Ken Evans
You are right that the extensive redox chemistry of manganese made it ideal for this job. And it is not rare (though not as famous as some other metal) so not hard to obtain.
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Welcome to the course @LucyCousins !
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An electrostatic interaction, but partially covalent too. Well done!
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James McEvoy replied to Ken Evans
Heme and chlorophyll have similar structures and it is likely that chlorophyll came from heme, evolutionarily speaking https://academic.oup.com/gbe/article/5/1/200/729709#
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James McEvoy replied to Mark Ward
Thanks for your thoughtful contribution @MarkWard. You are right that China is now increasing to a 3-child limit, but birth rates in that country remain low.
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James McEvoy replied to [Learner left FutureLearn]
Welcome to the course @MicheleCampanelli
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James McEvoy replied to Jo-Ann Giovannoni
It gets less mathematical next week!
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Equilibrium is reached when the free energy change is zero. At that point there is no net reaction.
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Oh dear! Let's hope some more learners besides Kirsten can manage this tricky exercise.
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James McEvoy replied to Marie G
These ion gradients give each cell a source of energy which they can use to do work, like transmitting nervous impulses, or moving compounds around. It's a bit like a hydroelectric power plant, using the potential energy stored in the water to drive other processes.
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Yes a kind of 3D L shape...
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James McEvoy replied to Mark Ward
Yes, he's a superb writer on bioenergetics too.
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James McEvoy replied to Sarah Rashina
Glycolysis never happens by itself. What happens to the pyruvate when the yeast begins to respire?
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James McEvoy replied to Ken Evans
Right, we've filled in some details but the broad picture here has remained the same.
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Glad to hear it and thanks for the feedback @AdamNDIFOR
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James McEvoy replied to Ken Evans
Very thorough, well done @KenEvans
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This course is more about energy than environmental toxins, @JohnDuffey , but I hope you find it interesting anyway.
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Great to have you on board @StephenJohnson
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I hope so, @RosalindM !
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Right, it's a delicate question as to whether a big public health challenge always deserves the name "epidemic". I tend to think not, not others have different views.
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James McEvoy replied to Ken Evans
Good question. Because mitochondria make ATP in their membranes it is more energetically efficient for the cell to contain lots of little mitochondria (with a large surface area : volume ratio) than a few big ones.
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James McEvoy replied to Ken Evans
Definitely true, good point @KenEvans
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James McEvoy replied to Marie G
Sure - and those compounds might be stored in the wrong place, too. Non-alcoholic fatty liver disease has become quite common, for instance.
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James McEvoy replied to Marie G
That’s right - although our skin does use solar energy to synthesise vitamin D, so it’s important in that sense.
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Welcome to the course, @AdamNDIFOR .
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Welcome to the course @AliceBarrell !
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Good question @NefiseArıt . There are a number of techniques, and some of them are described here https://en.wikipedia.org/wiki/Respirometry
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James McEvoy replied to Maria Grigg
Yes, smart meters are a great way to learn about your domestic energy usage.
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Welcome to the course @NefiseArıt ! I hope you enjoy it.
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Welcome to the course @MariaGrigg. Always good to get out of your comfort zone!
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Welcome @CarolMeasures !
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James McEvoy replied to John Sloman
Thanks for sharing @JohnSloman
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Welcome to the course @LynneoliviaLuckhurst !
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James McEvoy replied to John Sloman
Right.
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James McEvoy replied to Marie G
Of course when I say "reduction of oxygen gas" I mean giving it electrons, not reducing its quantity. The addition of oxygen gas to the atmosphere was of revolutionary importance, as we'll see in Week 3.
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James McEvoy replied to John Sloman
I'm no Trekkie, but I do know about dilithium crystals.
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James McEvoy replied to Jo-Ann Giovannoni
Right... Exothermic.
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James McEvoy replied to Marie G
That's right. The hot molecules used some of their energy to expand the space, pushing the lid upwards against the force of the virtual finger.
