Amino acids+Plasma membrane

[Snorlax]

Some answers to my questions on Amino acids/the plasma membrane would be much appreciated! I'm finding difficulty in understand these...

Why does the Hydrogen+ transfer from the carboxyl group to the NH2 group?
Is it due to pH levels?
What would happen if the Hydrogen stayed with the carboxyl group?

In the process of osmosis and even diffusion, i dont understand how water molecules/ions/etc that pass the hydrophilic heads of the plasma membrane, pass though to the hydrophobic parts of the membrane to enter the cell...HOW?

Explanations would be much appreciated!

[chisel]

Some answers to my questions on Amino acids/the plasma membrane would be much appreciated! I'm finding difficulty in understand these...

Why does the Hydrogen+ transfer from the carboxyl group to the NH2 group?
Is it due to pH levels?
What would happen if the Hydrogen stayed with the carboxyl group?

In the process of osmosis and even diffusion, i dont understand how water molecules/ions/etc that pass the hydrophilic heads of the plasma membrane, pass though to the hydrophobic parts of the membrane to enter the cell...HOW?

Explanations would be much appreciated!

Sorry, but those first three questions weren't really exposed to me at all last year, so i got no idea... but i do know the last one i think:

i'm pretty sure its quite simple and there are two other terms that need to be familiarised with - lipophobic and lipophilic. Anyway, ozmosis is purely to do with water, however you say you dont understand how a molecule passes through the membrane, well there are three types of diffusion:

1. Passive: this is when a molecule literally just crosses the membrane with no aid (from a carrier for example) it does this because it is LIPOPHILIC (fat loving) and so it can cross through the fatty acid tails as it 'loves' them.

2. Facilitated: this is the same as Passive, but a protein carrier/ channel is required. This is because the molecules wanting to cross the membrane are not LIPOPHILIC, instead they are LIPOPHOBIC (fat hating) and so they cant cross through the fatty acid tails because they 'hate' them.

3. Active: this is where a molecule goes against the concentration gradient (normal flow of molecules) and so ATP is required. Anyway this is usually requires a protein carrier.

MAN, that gave me a headache just thinking about all that stuff again... i hope i remembered it right as it was the first topic i learnt, and i hope it truly helps you (well the last question at least)
Best of luck for Bio this year, and if you ever need a hand PM me and i'll be sure to help!
 

[Scooby]

Some answers to my questions on Amino acids/the plasma membrane would be much appreciated! I'm finding difficulty in understand these...

Why does the Hydrogen+ transfer from the carboxyl group to the NH2 group?
Is it due to pH levels?
What would happen if the Hydrogen stayed with the carboxyl group?

In the process of osmosis and even diffusion, i dont understand how water molecules/ions/etc that pass the hydrophilic heads of the plasma membrane, pass though to the hydrophobic parts of the membrane to enter the cell...HOW?

Explanations would be much appreciated!

Some substances pass more easily through the phospholipid bilayer than others. It's not as if a substance either can or cannot pass through it. Water molecules can pass through pores in the phospholipid bilayer, but not easily as something like a fat or oil. There are also specialised channel proteins called aquaporins through which water molecules may enter or exit a cell.

Yeah, water is a polar molecule. The hydrophobic tails of a phospholipid are, well, hydrophobic (non-polar). Non-polar molecules may not mix well with polar molecules, like water, but it's not as if they repel them. The hydrophobic tails don't repel water molecules, they just don't have a great affinity for them

Ions generally enter or exit a cell via channel or carrier proteins, as do polar molecules

[Snorlax]

Lipophillic and lipophobic are new terms to me Thanks for that!
But in relation to osmosis, water is polar...Yet the hydrophobic parts of the plasma membrane are non-polar...how does water move through?

EDIT:
Ahhh thanks Scooby, my mind was set as if the hydrophobic tails repel any polar molecules...that clears that up..
"Aquaporins"? new term thanks.

[Scooby]

Lipophillic and lipophobic are new terms to me Thanks for that!
But in relation to osmosis, water is polar...Yet the hydrophobic parts of the plasma membrane are non-polar...how does water move through?

EDIT:
Ahhh thanks Scooby, my mind was set as if the hydrophobic tails repel any polar molecules...that clears that up..
"Aquaporins"? new term thanks.

Yeah, just remember - polar molecules and non-polar molecules aren't attracted to each other (they don't have a great affinity), but they don't repel each other. Polar molecules can sometimes pass through the phospholipid bilayer (not very easily), but usually enter or exit a cell via channel or carrier proteins. Non-polar molecules usually pass through the phospholipid bilayer pretty easily

Hope that helped! 

[Snorlax]

Also, just curious...What are the properties that make ethanol(alcohol) have the ability to move through the membrane easier? I just would of thought the size...but any other reason? is it non-polar?

plus, any help on my question about the amino acids would be nice!

[paulsterio]

Also, just curious...What are the properties that make ethanol(alcohol) have the ability to move through the membrane easier? I just would of thought the size...but any other reason? is it non-polar?

plus, any help on my question about the amino acids would be nice!

It'd be the same reason why water diffuses through the membrane

It's a small molecule, albeit polar.

[slothpomba]

It's been awhile since i've done bio (thats my disclaimer) but i highly doubt you need to know anything related to the first chunk of your post.

The second might help for your intuitive understanding but again, i really dont think you need to know that either. It sounds more like a 2nd or even 3rd year level uni type question ("How" not "What").

All you really need to know about osmosis and diffusion is that it operates on a concentration gradient.

[Scooby]

Yeah, the size of the molecule is important as well

I'd be really surprised if this popped up in your exam though

[Snorlax]

oh thanks...please correct me if i'm wrong...but trying to sum this all up:
So non-polar molecules diffuse across the plasma membrane quicker compared to water diffusing across? (if there were no concentration gradient and the size of the molecules were similar-same)

[Stick]

If there was no concentration gradient then diffusion/osmosis wouldn't occur. But yes, if the conditions and variables were very similar, a non-polar, lipophilic substance will cross the plasma membrane at a faster rate than a lipophobic, polar substance (eg water).

[Snorlax]

Ahh okayy thanks guys, appreciate it!

[slothpomba]

If there was no concentration gradient then diffusion/osmosis wouldn't occur. But yes, if the conditions and variables were very similar, a non-polar, lipophilic substance will cross the plasma membrane at a faster rate than a lipophobic, polar substance (eg water).

That's kind of true but it kind of isn't either. Molecules would still be moving around, it's not like they freeze or anything. Say the contents of a cell are isosmotic with the fluid outside of a cell, it's not that molecules have stopped moving between the external enviroment and the cell, it's just that they're leaving and entering at the same rate. So, there is movement but there is no net gain or loss.

It's just something important to point out. It could pop up on an exam or something.

[Russ]

Your questions about the amino acid proton movement (from COOH to NH2 etc.) is chemistry, not biology and isn't examinable in the Bio curriculum.

[paulsterio]

oh thanks...please correct me if i'm wrong...but trying to sum this all up:
So non-polar molecules diffuse across the plasma membrane quicker compared to water diffusing across? (if there were no concentration gradient and the size of the molecules were similar-same)

What do you mean by quicker? Without a concentration gradient, there would be no NET movement, so at any particular time, the concentration on both sides will be the same anyway. They're not changing, so they can't be changing quickly or slowly.

If you're referring to the flux, i.e. how many molecules pass through a specified area - then you won't really have to know this because it's well out of VCE and definitely well into the domains of physics and maths. Have a read if you're interested though http://en.wikipedia.org/wiki/Fick%27s_Law.