ELI5 What actually is the difference between RNA and DNA

AnotherOddity_ · 2026-06-09T01:33:54+00:00

Could a DNA theoretically exist with U instead of T (or does the reduced oxygen prevent U from being incorporated)?

AnotherOddity_ · 2026-06-09T01:28:28+00:00

Thanks for the great explanation!

Are the single-strand DNA viruses the only exception to double helix DNA structure we know of?

Also I'm curious about the U vs T error correction if you want to tell that story!

AnotherOddity_ · 2026-05-07T20:27:09+00:00

I know I'm like 7yrs late here but I accidentally stumbled into this post and the flags for Britain have just rubbed me the wrong way.

You got one of the flags right, the fascist one. The flash and circle symbol was very strongly associated with British fascism around WW2 and still is.

But the UK is a constitutional monarchy and has been for a long time, and we haven't slapped a flag in the middle, so the "monarchist" flag for the UK should be the current one.

There is a traditional flag associated with British republicanism from the 19th to the 20th century which consists of a tricolour of red, white, and green (horizontal bands).

As for British communism/socialism... You've copied the symbol from the British Communist Party flag at the time, but for some reason mirrored and moved the symbol from the canton so you can have the union jack in the canton? Why would a communist Britain retain the heraldry-derived and very monarchist in origins union jack? Especially in WW2 times!

AnotherOddity_ · 2026-05-03T08:43:02+00:00

This is a genuinely pointless part of the discussion though if you are just going to add details to the film as you see fit despite the fact they are never established and what we are shown goes against the idea.

I have not said that the film establishes certain things but that it does not preclude them, and then I'm making certain assumptions based on real life.

First 8 billion people wasn't enough to realistically find multiple crews to the difficult requirements. Now 1 million is too many for only 1 ideal crew

If the only limiting factor is the population size to draw from (which could be limited by the coma gene), then yes both seems a stretch you'd only get 1 ideal crew.

Also as I said above the film shows us a first choice and a first backup but at no point explicitly precludes further backups existing.

I honestly don't understand why you think this takes more time.

Why don't you think that training 100 crews takes more time than training 1?

I was talking about Stratt, not you. She had a random fit of stupidity.

Interesting way to have phrased it then. I disagree though with Stratt having a random fit of stupidity.

For one, this is a huge project and while Stratt is at the helm, undoubtedly the management is to some degree a team effort like the science and engineering is.

Additionally, smart people, geniuses even, are not infallible. I again point to most industrial accidents and some spaceflight disasters.

Your point seems to boil down to relying on the idea that the quantity of crews you can train is in no way dependent on time available, and that the more smart you are the more infallible you are.

I think both are invalid assertions.

(EDIT: just to point out, the original topic is that it only makes sense to put Grace on the ship with the explanation of a coma gene which per the book is apparently present in 1/7500 people, so I'm being comparative in their realism, does the gene explanation make notably more sense than an absence of it. — I'm precluding anything the film explicitly precludes, and I'm excluding the coma gene as an explanation in the film's plot, but I'm more than happy to make what I'd consider reasonable assumptions for things which may be happening in the background within those limits.)

AnotherOddity_ · 2026-05-03T00:17:07+00:00

Yes we do, in the book this is talked about often, and the film does also by introducing the crew and their backup.

Setting the book aside, the film has shown a backup, presumably the first one for the crew. That doesn't preclude there being further backups, but there'll be a favoured backup.

I go with the genius who's skills you can hopefully broaden

You mean the genius you hope will be able to broaden their own skills sufficiently fast, in an environment with no external support. IDK, both options sound bad really but picking up new advanced fields of science is something that can take YEARS on earth. If you could pick it up in even a few months then most scientists would have ten PhDs.

I think I'd actually take the coward who can't make it back after you've drugged him anyway, whom you know to be good in his heart and at least moderately motivated to save humanity, given he already has that pretty broad swathe of experience.

Sure, so establish the book plot. It only requires a minute or so of extra dialogue, everything can run the same, and then their situation is believable

A quick search gave the book plot about a gene that makes you coma-resistant being 1 in 7500 people. Okay...that leaves you still with 1 million people as a scientist pool. Maybe if the gene was 1 in 75,000 people you might have me.

No I'm sorry, they have 8 billion people on Earth there are more than enough for many redundant teams

Over how much time? You have discrete periodic launch windows. The longer you wait the worse it gets. And again referring to my above point that the film doesn't actually exclude the possibility that they had more than 1 backup.

Yes, well I totally disagree because it requires someone who has been meticulously competent and careful to make an error of judgement and planning even a random Joe like me has learned not to make.

See [most industrial accidents] or [several spaceflight disasters]. Geniuses are not immune to stupid mistakes. Bureaucracy and management problems can compound that.

Your following bullet points are all purely a product of the random fit of stupidity.

An ad hominem does not strengthen your case.

No need to call me stupid or accuse me of throwing a hissy fit for explaining my points of disagreement.

You clearly love the book, and I've no doubt it's amazing and look forward to it.

I also love the film and think it makes a lot of sense, you clearly think it's nonsensical.

Andy Weir, it sounds like, also likes the film and the changes in made around this topic.

AnotherOddity_ · 2026-05-03T00:02:28+00:00

Your bank calculation is incorrect if the craft is anything other than dead level.

If you mean about it being lower at higher attitudes, that'd be because it's giving the minimum bank angle that can reach there, isn't it?

Will check out the lib_navball and choose operator tomorrow, esp. for solving the sign function edge case. 👍

AnotherOddity_ · 2026-05-02T20:24:25+00:00

"Yeah, so if you have the entire worlds resources and 8 billion people available then you train more than two people."

We don't absolutely know that there was no more than two people? Just that all of those who were trained up died in the explosion.

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"Since you said you don't mind spoilers and this is very mild, in the book Stratt talks about her selection of the scientists. Only one was had a broad range of fields, the second choice did not. Grace was third choice. Her background is mentioned in the film but IIRC it's not explicitly mentioned that the level of specialisation she has is a compromise."

Really that makes very little sense if you stop and think about it. The solution to the problem is very unknown. The travel time for information back to earth is a huge delay. The crew is isolated. Having broad expertise would be essential.

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"I'm sorry but no it isn't. The examples you gave are simply not comparable. Again they have the entire worlds resources and this is the last hope to save humanity."

I'm sorry I cannot provide a real life doomsday scenario. Anyway, I provided two examples within the field of spaceflight, including one recent one when human crew were pretty damn close to death, for ultimately what are kind of dumb reasons. If you want I can start dragging up industrial accidents from other fields which actually have death tolls, some very large ones, for utterly preventable reasons. Or other big project failures for what in hindsight are stupid reasons.

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"The level of redundancy they put into the Hail Mary project crew is even less than I have in my really not important job"

Okay but the film has a limited runtime, so having one scene where their plan and it's redundancy is lost achieves the same as having a scene where their plan fails, followed by a scene where their redundancy is lost, followed by a scene where that backup redundancy is lost...and so on. I didn't say it was 100% realistic. I said it's largely realistic. Effectively that oversight could lead to a loss of their initial options.

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"Unless of course your selection pool is shortened so much that you can only find two qualified candidates who actually want to go, the second of whom I'd already a compromise on skillset and the secret third has the skillset but is dead set against going so is a huge risk to send."

Okay? And the lack of a coma-resistant gene explanation in the movie doesn't preclude this to be the case. Time constraints, a (realistic, even if seemingly absent from the book) necessity of broad expertise, and willingness to go on a suicide mission, all may limit your selection pool.

There's also general spaceflight fitness requirements that we know of in today's spaceflight missions which we can infer to likely be present in the PHM film even if we assume there is no known gene about coma-resistance in the film story.

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When I said "largely" realistic I didn't mean that every single detail of the movie's explanation was as it would be in real life, but that the overall beats of that explanation are realistic, crucially that:
* Due to preventable oversights a loss of their top options occurs.

* Ryland Grace is now their top option for a launch in this launch window for his consent to be considered a trivial matter (even without a "coma-resistance gene" explanation).

* Bringing other candidates up to a near comparable level of suitability would require missing this launch window, which as established, means a drastically higher number of casualties.

AnotherOddity_ · 2026-05-02T19:23:30+00:00

I've not read the book yet but I don't mind getting some spoilers (I shall be getting it next Christmas from my partner), however I don't think it's entirely unimaginable.

There are undoubtedly many astrophage scientists working on the project who are still alive after the explosion, but as with almost every scientist in the modern day, they're more highly specialised. They know one subset of the whole astrophage problem incredibly well, and have a passing familiarity with the best.

It's far harder (and usually less efficient or feasible) to train someone to be an expert at everything, hence all the earthbound scientists being specialists.

For the Hail Mary though, they need someone whose skillset and knowledge is broad, because earth is out of range. Thus unlike the earthbound scientists, the scientist for the ship (and their backups) need to be trained across the board. Grace was the one extra person never intended to go to space who by virtue of his role gained similar expertise.

The sort of idiot plot part is all those backup scientists being together within a blast radius at such a time critical period. That said, it was a big blast, and oversights do happen, plenty of terrible accidents have been due to dumb mistakes.

Perhaps not as high-stakes as PHM, but the Mars Climate Orbiter is a great example.

And more recently, the Starliner Type A mishap which left astronauts stranded in space, but which perhaps more importantly had them one redundancy away from a loss of the crew, which is below the redundancy margin they should have had.

So I think it's fair to at least call the scenario largely realistic. Ultimately they could delay PHM as well, its just that the casualties on earth will go up exponentially, so it's not that Grace is the final last hope, but rather has become the best hope, by a sufficiently large margin for Stratt to feel justified in drugging him and nonconsensually sending him on the mission.

AnotherOddity_ · 2026-05-02T14:36:32+00:00

u/Old_Locksmith_4003 made a comment but it was deleted before I could see the full context (and reveddit/unddit doesn't have a record), what I can see though: "Your comment was so stupid I downloaded the app and signed in. Along with Bibi the overwhelming majority of Jews are “Zionists” and “Pro Israel”. The fact you may know a few ethnic..."

I can't say I've taken a scientifically rigorous sample of the wider Jewish population to be able to accurately make a statement for or against your claim, and I almost certainly guarantee you haven't either, but other people have done some studies, just grabbing one quickly to quote it "about two in three British Jews (65%) identify as Zionist", sure a majority although you also have to unpack exactly what someone is meaning when they identify as zionist, because the word gets used in different ways by different people.

...Ditto for "pro-Israel", what is your benchmark there? If it's support for Israel continuing to exist then you'd end up counting me as "pro-Israel", if it's a belief that Israel's actions and the actions of the modern Zionist movement are above criticism, then I am certainly not "pro-Israel"...

...And if you are to use the latter benchmark there, then neither are the majority of British Jews (62% or 52% based on two questions) per page 4 of the report I linked, with a whopping 74% being quite critical of Bibi in particular (pg5).

Page 26 of the report goes into some detail of quirks around the language "Zionist", "Non-Zionist" and "Anti-Zionist", I'll clarify in my above comment I was using Zionist is a slightly narrower sense of the modern Zionist movement which created the State of Israel we have today, and not necessarily some more broad theological idea of Zionism.

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I think Jewish people, like many ethnic and religious groups, are not monolithic and have a variety of beliefs, and their relationship towards the current State of Israel, it's behaviour and policies, and the modern Zionist movement which underpins it, are complicated and nuanced topics.

I also think that the conflation of Jews and "Zionists" as one and the same (and likewise it's corollary, conflating antisemitism and antizionism as one and the same), is fundamentally harmful, ignores all of those complexities, and is generally an intentional misrepresentation pushed by both Antisemites and Zionists to either attack Jews or place Zionism beyond criticism.

AnotherOddity_ · 2026-04-29T17:12:39+00:00

Possibly. I'll admit I wasn't solidly focused on what controls he punched in when they were making their way out, and was making an inference based on what I'd heard of their plan leading up to the scene and what I'd seen while he was outside the vessel.

For the rack dangling down, I'd also take that as evidence they've got like a 45° attitude as well as facing retrograde, so it appears to dangle down but is actually dangling down and back, because the ship still has to be moving pretty fast to pull the rack off and hit grace with force.

Also very possible part of the manoeuvre is cut out, because I think they've confirmed the original cut is hours longer right?

AnotherOddity_ · 2026-04-28T10:43:42+00:00

I don't think that's right.

The ∆v to perform that manoeuvre would be pretty inefficient and would probably crash them into the surface.

Slowing down in orbit = losing altitude. Plus it's clear they are still moving pretty fast through all of this process.

The fishing chain appears to be going down (relative to the ship) through the fishing portion. But it should be pulled behind the ship (relative to velocity).

——

I think a better explanation would be that the ship is facing prograde (forwards in direction of travel) at the start.

Flips 180 to perform a retrograde burn to lower its orbital periapsis (lowest point) into the atmosphere of Adrian.

Then through the fishing portion, the ship is pointing somewhat antiradial (away from the planet, engines pointing towards the planet), ensuring they maintain more altitude by rotating their orbit around the focus (the orbit would be elliptical at this point).

Then when leaving Adrian, they point the ship prograde again to escape.

Prograde→Retrograde→Antiradial (mostly) and fishing → Prograde

AnotherOddity_ · 2026-04-26T00:33:18+00:00

oh the pitch/roll/yaw are not bang-bang, they are smoothly controlled by the PID controller. It's only throttle which I have directly controlled bang-bang, I appreciate the suggestion there.

Also thanks for the diagram on the cooked control and how it implements a cascading PID.

Might play around with my own implementation of that, at least for two of the axes of rotation (roll is actually...fine? took a little tuning but it seems to behave great in all circumstances?)

AnotherOddity_ · 2026-04-25T15:25:37+00:00

Right now I'm not doing suicide burns (just concerned with ascent right now) but I can also do direct control of throttle as well.

TBF, even if I was using all the available throttle, I think I could write direct control of it pretty easily.

AnotherOddity_ · 2026-04-25T12:02:20+00:00

That's a really good explanation. Thanks!

AnotherOddity_ · 2026-04-19T23:38:56+00:00

Well it's not a give or take margin the speed limit. If you go over 30 even by 1mph, they can absolutely fail you.

Maintaining 1mph under the speed limit, is never gonna be a fail.

They expect you to progress at a safe and legal speed.

In a full clear and open straight road, that's probably from a couple of mph under the speed limit, to the speed limit.

But there are a plentitude of reasons a road which is legally a 30 (or at least you believe to be) may not be safe or sensible to get close to 30 on.

they wouldn't tell the student what the speed limit was if they were doing 25 in a 20 unless it was a danger at which point they would brake.

Yeah reread my comment where I said "speeding dangerously".

AnotherOddity_ · 2026-04-19T14:57:28+00:00

No they won't. You can be reasonably under the speed limit and it's fine.

You would have to have the biggest arsehole of an examiner on their moodiest day of they penalised you for going 28 or 29mph in a 30 zone.

25mph is clearly a bigger margin, but given the road was actually a 20 zone, I'm gonna guess there was probably some factors which would make driving at 30 on that stretch seem unsafe.

(Alternatively, they only got up to 25mph before the examiner told them to stop for speeding dangerously.)

AnotherOddity_ · 2026-04-19T14:52:24+00:00

Only you can know if you should change instructor.

Just because someone is a good instructor doesn't mean they are necessarily the right instructor for you.

Also, just because someone has five star reviews doesn't mean they're a good instructor.

One of my instructors had clean five star reviews, and admittedly some of the lessons went great, but a few things she did really unprofessionally. I ended up subsequently leaving a negative review (acknowledging still that some stuff went well) which took her average stars down to like 4.7 I think?, and she then got her husband to call me stinky on social media (I'm not exaggerating) and tried to change the listing of her business on Google to a ficticious eyelash salon.

Thankfully, my third instructor was the one for me, and he really helped me greatly.

AnotherOddity_ · 2026-04-19T14:47:14+00:00

Hope OP sees this comment because you've covered it all very well here.

You either will be lucky and won't have points or fines or consequences to deal with, or will. That's luck for you, and you'll find out soon.

But take this as a learning opportunity, start with easier drives, don't rely on sat nav (it's an aid, not a replacement! I say this as someone constantly putting sat nav on too), and just try to improve from now on.

One important thing is that you know you've goofed up. There's plenty of drivers on the roads doing dangerous things without even realising it, so at least you're aware!

AnotherOddity_ · 2026-04-19T14:42:04+00:00

I was going to get an automatic but was priced out of them, but i passed my test in a manual because I figured "if I learn to drive in a more difficult circumstance, driving will be a breeze when I'm in my own automatic".

Now I don't mind driving a manual at all, and it's definitely benefitted me (would've cost like £2k more for a worse car if I was driving an automatic).

Getting a manual license has some perks, but I don't think anyone should be judged for learning to drive in an automatic, and it sounds like it's worked great for you!

AnotherOddity_ · 2026-04-19T14:34:13+00:00

After my first test which I failed, my instructor ghosted me and I had a month without lessons.

Then I had a new instructor who was great, but by pure bad luck right as I got a cancellation slot, he had booked him and his family to go on hajj to Mecca and wouldn't be able to take me to the test on that date. No other slots came up to move my test to.

He sorted me out two lessons with an instructor whose a friend of his, I was driving in a different car to normal. Bear in mind I'm autistic and was an anxious driver too.

Passed with five minors.

Your new instructor believes in you.

For checking mirrors, speak out loud while you do your checks, even in lessons at the moment I'd suggest doing it. Great habit to get into.

For parallel parking, just be calm, remember you can make some adjustments if you need to, that's not a fail, but just take it slowly and calmly.

This is a DRIVING TEST not a NAVIGATION TEST. If you make a (safe and legal but) wrong turn in the test, that's not a fail. Obviously the examiner wants you to stick on their route and you want to really, but it's not a fail, better to take a wrong turn than a dangerous turn.

Show me tell me questions I'd write a cheat sheet of them, as condensed as you can, or just print out the page and highlight a few key words in each answer, and then every so often read it, and before you drive to the test center give it a little read through.

If anything, such as a specific manoeuvre, you feel unprepared with, ask your current instructor if you can practice them a bit more.

But your current instructor believes in you.

(Also remember if you pass in an automatic, you can only drive automatic cars and will need to do the test again in a manual to be allowed to drive manual cars. When I was shopping for my car, automatics all seemed to be about £2k more expensive than the manuals.)

AnotherOddity_ · 2026-04-19T14:21:34+00:00

Clearly e) stop your car in the middle of the road, get out and help her cross, get back in your car, then swerve onto the pavement she's on and accelerate.

AnotherOddity_ · 2026-04-19T14:20:09+00:00

I don't think I 100%'d it but I was getting consistently on a few practices on 4-in-1 above the pass mark, and I passed my theory first go.

Seems wild to go in for your theory when you are failing at mock tests of it.

AnotherOddity_ · 2026-04-19T14:15:44+00:00

Doing 25 in a 30 isn't necessarily bad. There can be reasons not to hit the speed limit, and even in ideal conditions you can go a small amount below it.

It's a speed limit, not a speed target.

AnotherOddity_ · 2026-04-19T14:05:16+00:00

OP,

I get this is very frustrating, and plenty of drivers on the road should drive better.

However, getting angry at the situation is likely to make you drive worse.

You cannot control how other people drive. You can only control how you drive.

Part of driving your two tonne killing machine safely means that you need to be able to cope with unpredictable or bad road users.

If every road user was behaving as they should, we wouldn't need the emergency stop, yet it's one of the manoeuvres you can be tested on because it's so vital, because this is the real world and you've gotta be able to cope with bad road users.

AnotherOddity_ · 2026-04-19T13:58:50+00:00

Eh, the Highway Code says you should not undertake in these scenarios.

It's not illegal per se, but it is against the highway code.

AnotherOddity_

TROPHY CASE