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Science - please help!!! - IceCream - 2010-09-16
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Science - please help!!! - JimmySeal - 2010-09-16
IceCream Wrote:But, Hydrogen ions H+ are made by giving up protons. So, what makes atoms give away their protons? What then happens to the negatively charged thing thats left? Is it stable?Atoms can't give up their protons (unless radioactivity is involved). H+ ions occur when a molecule gives up a proton (which is the H+ ion). The classic example of this is a water molecule giving up a proton to produce an OH- ion and an H+ ion. The OH- ion has 10 electons and the H+ ion has none.
Science - please help!!! - rigol - 2010-09-16
IceCream Wrote:2. DNA.Why does DNA form a double helix (aka, why did it evolve that way)? Think of semiconservative replication.
Why does DNA consistently form a double helix, but RNA folds in on itself and things like that? Why wouldn't RNA make a double thing too, or DNA just fold in on itself? There's only Uracyl that's different, but it still bonds in the same way as Thymine right?
Chemically, RNA can form double helices too (A-form helices, dsRNA = double strand RNA is the genetic material of some viruses for example). As to why RNA is not normally found as a double helix: during transcription only one strand of DNA is being transcribed, resulting in only one strand of rna. But for forming a double helix, two opposing strands are needed.
(Hope that was comprehensible, English is not my native language ^^)
Science - please help!!! - jcdietz03 - 2010-09-16
The H+ ion has zero (零) electrons! H+ ion is another word for proton because that's all it has (one proton only). The normal hydrogen atom has one electron, but it doesn't exist in that state in nature. It is usually found bound with another hydrogen atom.
When water dissociates, The OH takes an electron from the H because OH is -1 affinity (meaning it wants to get electrons) and H is +1 affinity (meaning it wants to give up electrons, or doesn't hold them strongly).
OH- is pretty unstable. It readily combines with H+ to make water. OH- can also combine with other things; I'm not a chemist so I don't really know.
Science - please help!!! - rigol - 2010-09-16
RNA's can be a very complex subject and I don't know how deep you have to dive into that, so I try to keep it simple:
In human cells, RNA exists mostly as relatively short strands. Mainly, it's an information "shuttle": it transfers the information from the DNA to the ribosoms for protein synthesis. There is not a specific amount of RNA in each cell that I'm aware of; in cells with high protein synthesis activity there is more, in cells with low activity less rna, because rna is synthesized during transcription and this is a highly regulated process because it costs energy.
So, what happens to the RNA the rest of the time? Basically, after rna is transcribed (yes, just a single strand), it gets translated into aminoacid sequences which proteins consist of. At some point after being translated (often more than one time) it breaks down on its own (mRNA is not very stable) or gets broken down by other enzymes into nucleotides, which then can be used again by the enzymes which transcribe the DNA into RNA.
Happy to help you, good luck for your entrance exam!
Science - please help!!! - JimmySeal - 2010-09-16
IceCream Wrote:oh, wait... why does the OH- keep the neutron, and not the H+? And why does Oxygen sometimes make normal covalent bonds with Hydrogen, and at other times takes just the electron + neutron?What neutron are you referring to? Atoms don't give up their neutrons or protons unless radioactivity is involved. The only particles exchanged during normal chemical reactions are electrons. Just bear that in mind because you seem to be missing that.
The vast majority of hydrogen atoms don't have neutrons, but if the reaction were to involve a hydrogen atom with a neutron, it would stay with the proton, as they make up the nucleus and that doesn't change.
Science - please help!!! - jcdietz03 - 2010-09-16
IceCream Wrote:oh, wait... why does the OH- keep the neutron, and not the H+? And why does Oxygen sometimes make normal covalent bonds with Hydrogen, and at other times takes just the electron + neutron?Atoms never trade protons or neutrons. Only electrons. To get atoms to trade protons and neutrons, it takes enormous amounts of energy such as that found inside a star.
Science - please help!!! - Tori-kun - 2010-09-16
@ IceCream: Look through the topic "proteinbiosynthesis" - it covers all your questions on why/how/what (rna vs. dna). just a hint~
Science - please help!!! - Blahah - 2010-09-16
Hey Ice. Just to add to what others have said...
IceCream Wrote:1. Ions.An easier way to think about ions (if talking about atoms) is that an atom of a given element will always have a set number of protons - that's what defines it as the particular element in question. For example, hydrogen has one proton. Often, the number of electrons associated with the atom will equal the number of protons (this gives the most balanced state). If electrons are lost from a starting state of balance, you get a +ve ion, whereas if electrons are gained you get a -ve ion.
ok, so, a normal ion has either more electrons than it has protons, making a negative charge, or one less electrons than it has protons, giving it a positive charge.
An atom can become an ion only if a.) the outer shell of electrons is unstable and b.) the electronegativities of the two atoms concerned are very different, leading to a complete transfer of electrons from one to another.
But, Hydrogen ions H+ are made by giving up protons. So, what makes atoms give away their protons? What then happens to the negatively charged thing thats left? Is it stable?
Hydrogen ions are created when a molecule containing a hydrogen atom gets separated from the hydrogen in a reaction and the hydrogen leaves without an associated electron. Assuming that the hydrogen atom is not an isotope (i.e. it has the usual number of neutrons, in this case 0) then its ion consists only of a lone proton. For this reason you will often see H+, hydrogen ion, and proton used interchangeably.
Ions are not stable - they will form ionic bonds with other ions (either atoms or molecules). However, if you dissolve an ionic compound in a polar solvent (e.g. dissolving table salt, NaCl [sodium chloride], in water), the component ions will mostly stay as individual ions. Actually, they will continually bond with one another and then break apart again, but at any given time the majority of the molecules will be lone ions. This is because a polar solvent (like water) is made up of molecules which have a difference in charge from one end of the molecule to the other (called an electric dipole) due to unequal sharing of electrons between the components of the molecule. The attractions between the polar solvent molecules and the ions in the compound being dissolved are strong enough to pull the ions apart, which keeps them apart from one another (although, as I said before, they do actually continually bond and separate again). So, lone ions are in general not stable but in some situations they can seem to exist singly for long periods of time (like all that salt dissolved in the sea).
IceCream Wrote:2. DNA.Right! But RNA does actually form double helices, just like DNA does. In fact, because RNA nucleotides and DNA nucleotides can bond, you can get DNA-DNA double helices, RNA-RNA double helices and DNA-RNA double helices. The reason you don't always hear about the RNA double helix is because it's hardly ever at rest, always being formed and broken apart again. In the various stages of replication, transcription and translation, RNA molecules will take on looped structures, alpha-helices and beta-helices (the famous "double helix"), as well as formless swirly things. DNA in most cells will spend resting time (which, in a cell at optimum temperature is basically never) as a beta-helix, but also takes on other unpredictable shapes based on its current activity and the moisture content.
Why does DNA consistently form a double helix, but RNA folds in on itself and things like that? Why wouldn't RNA make a double thing too, or DNA just fold in on itself? There's only Uracyl that's different, but it still bonds in the same way as Thymine right?
Science - please help!!! - zachandhobbes - 2010-09-16
Are you self-studying?
Also this seems to be more chem than bio.
Science - please help!!! - zachandhobbes - 2010-09-16
Yeah, I'd suggest you get a textbook. It seems that your knowledge base is quite scattered.
A really, really good resource would be something like an AP Biology (from America) text book. Those are supposed to be like Bio 101 classes in college and would fit you well I think.
Science - please help!!! - jcdietz03 - 2010-09-16
Neurons transmit and receive signals electrically and via the use of chemicals called neurotransmitters. They receive signals via the dendrites and transmit them via the axon. I don't know how neurons "decide" when to retransmit a signal and when not to.
Current means moving electrons. That's all it means. When you see a "one amp" rated circuit, that means up to one coulomb (a unit of charge) per second can travel through that circuit safely.
Normal electricity is made of electrons, which aren't atoms. Electrons are part of atoms. Metal (which circuits are usually constructed from) has a bunch of properties - one is that its electrons are loose and can flow freely between metal atoms. This gives what on the macro scale is called conductivity which is one property of metals generally.
I don't think you can put an electrode inside a neuron. Since neurons transmit and receive signals electrically, you can excite a neuron by applying a voltage to it - this is what electrodes are for. The voltage doesn't have to be big (<1V usually works). fMRI is used when you want to observe neurons firing without influencing them. Electrodes may have been used in the past for this purpose but I don't really know.
Cells use osmosis to move materials with the grain. They use chemical pumps (and energy) to move materials across the grain (i.e. from lower to higher concentration). I don't know about Na+ and K+ specifically.
Electricity doesn't carry voice signals...sort of. This gets into how a radio works. If you have an oscillating electrical signal (I think you can design a circuit that does this given a power source but I'm not exactly sure) traveling inside an insulated wire, it will stay within that wire. If you have an electrical signal traveling inside an un-insulated wire, it will escape the wire and travel through the air. Depending on the oscillation frequency, the electrical signal traveling through the air will have different properties, such as how quickly it attenuates and how good is it at bending around corners. Also, these properties change depending on the length of the un-insulated part of the wire. We will now call the un-insulated part of the wire the antenna because that's what you call an un-insulated wire whose purpose is to transmit an electrical signal through the air (or some non-conductive medium). Then there's the whole bit about receiving a transmitted signal too. Then there's the whole bit about how do you transform a person's voice into an electrical signal so that it can be transmitted (this is called transmission). Then you have the bit about taking the transmitted signal, receiving it somewhere else, and processing it into audio (called reception).
Science - please help!!! - hereticalrants - 2010-09-16
Ah, electromagnetic radiation...
The way you explain it, it sounds like it is electricity(electrons or whatever) but it's all photons... from radio waves, to visible light, to x rays and gamma rays.
@Icecream
Sodium and potassium ions pass through the phospholipid bilayer at different rates-- and ions in general do not pass through it well.
This is why the nueron can create electric potential on the membrane through active transport-- it uses one ATP to exchange three sodium ions for two potassium through the transfer protein. This is done against the concentration gradient, so it does require molecular energy from ATP.
Get a good textbook, it can explain these things better than random forum users
You have a long way to go on those chemistry concepts...
Science - please help!!! - hereticalrants - 2010-09-16
IceCream Wrote:ok, cool, thanks JCDietz, i guess i can safely skip normal electricity then, since it's not really the same type of thing. Thank god lol. That voice thing seems complex!!I think he just rambled a bit. How complicated can sound waves being translated into electrical impulses possibly be, compared to, say.... the nature of the natural world itself?
Science - please help!!! - Aijin - 2010-09-16
IceCream Wrote:ok, cool, thanks JCDietz, i guess i can safely skip normal electricity then, since it's not really the same type of thing. Thank god lol. That voice thing seems complex!!Myelinated axons are only present in vertebrates it's important to keep in mind though.
And so, the current in neurons is only really from one Myelin Sheath to the next, i guess, because new ones flow after that...
Myelin sheaths basically work like this: the sheath is interrupted by sections of unmyelinated sections (called the nodes of Ranvier). There are no sodium channels between nodes, so the action potential (the electric impulse) can't regenerate along the nodes.
Instead, what happens is that when an action potential occurs at a node all the sodium ions that enter into the cell diffuse, and end up repelling all the positively charged ions in the axon, which pushes the chain to the next node, where the action potential then is regenerated.
There's a few bonuses to this: besides being far more rapid, it conserves more energy than if an action potential had to occur at every point along the axon, because in that case the sodium-potassium pump has to use energy to pump out all those sodium ions, whereas with a myelin sheath sodium ions are only entering at the nodes rather than the enter axon.
Quote:When you put an electrode on the inside or outside of a neuron, what exactly does it measure? Is it taking a sample of the number of +ve or -ve ions around it?Microelectrodes are inserted into the soma (the cell body) of the neuron, then another electrode is placed outside the neuron. That way both the interior and exterior are recorded in millivolts by a voltmeter.
Quote:Since Na+ always seems to flow into the cell, and K+ flows out of the cell, how does it manage to end up with more Na+ on the outside and more K+ on the inside?Sodium will always be around ten times more concentrated outside of the cell's membrace because the sodium-potassium pomp transports three sodium ions out whilst drawing two potassium ions in. Because sodium is positively charged, and potassium negatively charged, sodium WANTS to enter the cell, but the membrane is selectively permeable, so it cock-blocks the sodium
When the neuron is at rest (no action potentials occuring) the sodium channels are closed, so while it doesn't enter the cell it can be pushed out of the cell (by the sodium-potassium pump, which is active even while the neuron is at rest)The reason everything ends up normal again AFTER an action potential, though, is NOT because of the sodium-potassium pump . It's simply too slow. After an action potential peaks, the potassium channels open up, and they flow out of the axon. The potasium channels remain open even when the sodium channels have already closed, so that so much potassium leaves the membrane that eventually the membrane gets repolarized.
Science - please help!!! - liosama - 2010-09-16
hereticalrants Wrote:Ah, electromagnetic radiation...No sorry hereticaldkaslkas the way you understand it is also wrong. Though his explanation is a little muddled, and electricity doesn't travel through air, it can't. EM waves are generated by electricity.
The way you explain it, it sounds like it is electricity(electrons or whatever) but it's all photons... from radio waves, to visible light, to x rays and gamma rays.
Get a good textbook, it can explain these things better than random forum users
You have a long way to go on those chemistry concepts...
Also there is nothing wrong with asking questions on a forum with random forum users to at least get an idea/primer of things, then delve in deeper so there is a foundation to work upon.
Also ice, I recommend TTC for a high level understanding which is more important than anything, especially with the sciences, there are a good bunch of TTC physics and TTC Neuroscience lectures, though I havent seen either, they shouldn't be that bad, you can't be biased on raw science, so it won't be as stupid as the linguistics lecture by that John McHhorter dude
Best of luck with Kyoto daigaku
You'll do well my dear.
Science - please help!!! - TheVinster - 2010-09-16
You people... are monsters.
Science - please help!!! - hereticalrants - 2010-09-16
liosama Wrote:hereticaldkaslkas the way you understand it is also wrongI don´t think I said enough about the way I understand it for you to say as much. In fact, you repeated the only things I really did say on the topic.
... why am I even posting this? Defend your nerd pride! Yaaaaaar! Hahaha.
Science - please help!!! - ta12121 - 2010-09-16
TheVinster Wrote:You people... are monsters.一体何者？
Science - please help!!! - Aijin - 2010-09-16
Hey hey, I'm not a monster! Just a robot, gosh.
...You guys didn't REALLY believe Honda's orchestra-conducting robot was the true extent to our technology, did you?
Science - please help!!! - Hashiriya - 2010-09-16
WTF! (*throws in the towel)
Science - please help!!! - hereticalrants - 2010-09-16
I think when Aijin said that the sodium-potassium pumps were slow, she meant that they're slow in relation to the open protein channels that work by passive transport.
A "couple of miliseconds" is a really long time when you're talking about individual neurons.
Also, the majority of the neuron's energy is used in the sodium-potassium pump, even though it pretty much just helps obtain/maintain resting potential(among other things) by expelling excess sodium.
As she said, action potential is obtained simply by letting potassium concentrations do their thing and balance out on each side of the membrane. The sodium concentrations remain out of balance and provide the charge.
*this is an official statement of humility, as I have not studied this in a long time and may have no idea what I'm talking about.
Science - please help!!! - Aijin - 2010-09-16
IceCream Wrote:wow Aijin, i thought you were an arts student!!?!? How do you know this stuff in so much detail?!? But thanks...!!!At one point I was considering a career in behavioral neuroscience. I abandoned that of course, but I still have some left over knowledge from the coursework/labs and self-studying I did on it. To be honest though my knowledge of neurophysiology is pretty rusty; I was always far more fascinated by the psychology aspects of the field rather than the biology bits.
Quote:1. resting neuron.Yep, you got it. The concentration gradient and the electrical gradient are in balance (equilibrium potential to be more specific). The reason the inside of the cell is negative, though, is mostly due to negatively charged proteins inside the membrane.
inside of cell Na+ a little K+ lots less positive
-----------------------------------[ ]-------
outside of cell Na+ lots K+ a little more positive
So, the chemical force wants to push K+ outside, but the electrical force wants to keep it inside. This is why potassium channels can be open, because eventually the two forces on K+ reach an equilibrium and no more goes through the open channel. This accounts for the relative negativity of the inside of the cell.
Quote:4. The cell should return to resting potential. When the sodium-potassium pump is doing it's thing, it doesn't have all that much effect on the relative quantities of things, because it's slow. But with so much Na+ there, the equilibrium of the forces of K+ would surely be at a different point than it was originally, even though there are K+ channels left open?I think it'd be easier to explain this with graphs of the rate of entry of sodium, and the rate of exit for the potassium. I remember my behavioral neuroscience textbook had a lot of graphs for the action potentials/repolarization, and it really helped to understand the concepts. It's pretty hard to visualize neurophysiology just on explanations in words alone after all.
Therefore: How does the Na+ get out of the cell, so there is only relatively little there, ready for the next possible action potential, which can occur in a couple of miliseconds???
But yes, it doesn't go immediately back to the resting potential. Potassium ions flow out at a rate significant enough that the membrane becomes temporarily hyperpolarized due to all of the positive charges that are exiting with those potassium ions. But the hyperpolarization doesn't last long, and it DOES get back to resting potential before the neuron's refractory period is over.
In other words, to answer your question simply: The concentration gradient causes potassium to leave quickly enough that the resting potential is attained within those couple of milliseconds, so that the neuron is ready to fire again.
Action potentials are usually graphed with 1 ms as the measurement, so you'll be able to see exactly how fast the repolarization truly is.
Aha, found one
http://openwetware.org/images/thumb/a/a6/Action-potential.jpg/300px-Action-potential.jpg.png
Science - please help!!! - zachandhobbes - 2010-09-16
I learned about this last year in chem.
What happens is that the electrical action potential causes the channels to open up and the Na+ flows out through the opening.
Science - please help!!! - zigmonty - 2010-09-17
jcdietz03 Wrote:Electricity doesn't carry voice signals...sort of. This gets into how a radio works. If you have an oscillating electrical signal (I think you can design a circuit that does this given a power source but I'm not exactly sure) traveling inside an insulated wire, it will stay within that wire. If you have an electrical signal traveling inside an un-insulated wire, it will escape the wire and travel through the air. Depending on the oscillation frequency, the electrical signal traveling through the air will have different properties, such as how quickly it attenuates and how good is it at bending around corners. Also, these properties change depending on the length of the un-insulated part of the wire. We will now call the un-insulated part of the wire the antenna because that's what you call an un-insulated wire whose purpose is to transmit an electrical signal through the air (or some non-conductive medium). Then there's the whole bit about receiving a transmitted signal too. Then there's the whole bit about how do you transform a person's voice into an electrical signal so that it can be transmitted (this is called transmission). Then you have the bit about taking the transmitted signal, receiving it somewhere else, and processing it into audio (called reception).This is actually partially incorrect. You can insulate an antenna and it will still work. Think of your mobile phone, the whole thing is encased in plastic (an excellent insulator). Insulation prevents conduction of electric charge, it does nothing to attenuate the associated magnetic field. Plastic is transparent to frequencies considered radio waves (obviously not visible light though, well, unless the plastic is transparent lol). To prevent EM waves propagating from a wire carrying alternating current, you have to shield the wire. This shield has to be metallic, completely surround the wire (obviously insulated from it) and be connected to ground. You're basically wrapping the wire with another antenna that absorbs the waves and diverts the energy to ground.
Anyway, a bit off topic...