biologay

[run-bandit]

I don't get why 'no charge' is considered lipophillic (and hydrophobic, since not polar)

Shouldn't it be neutral - absolutely nothing-phillic or -phobic?

This 'neutrality' apparently allows small neutral particles to get through the phospholipid bylayer of the plasma membrane!

How can this be since there is hydrophillic ends on either side which will repel it? And even if it did get through one, wouldn't it prefer to stay in the centre?
     

[TrueLight]

hmmm not sure if this answers ur question completely but heres something...

someone who does biochem...or more chemistry could probably explain it to you more...about the charges and such

the phospholipid in the cell membrane has a polar head and a nonpolar tail.... the head has a slight negative charge from the phosphate group...but the tail is not charged, since its non-polar ... its made up of 2 fatty acid hydrocarbon chains... try googling an image of one

small non-polar molecules would go through via simple diffusion
water goes through too even though its polar through aqua porins

other charged ions and proteins and large molecules go through proteins that are embedded in the membrane

na it wouldn't get stuck in the centre... remember there is a concentration gradient that drives the movement


maybe this will help
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=mboc4&part=A1861

[stonecold]

true light pretty much hit the nail on the head.
let me tell you something about vce.  just learn and accept what your told, don't question it.
you'll be much much better off for it.

[TrueLight]

lol ... very true for yr 12... although i was one of those who wanted to know why this why that...lol and teachers didn't know the answers
just learn the basics!

[stonecold]

lol yeah.  i'm not saying that you shouldn't question things, because natural instinct makes you want to, but sadly vce is just one of those things where you have no choice but to take everything you are taught as gospel.

[simpak]

Okay think about what you just told me.  You told me something with NO CHARGE is lipophilic.
In this instance, we think of it has having no charge.  Ignore this non-polar business.  That just means it won't dissolve in water.  That's why it's drawn to the fats; imagine dropping a whole drop of oil in some water, it would sit together and not separate out into the water.  When you only have one particle it sits together in the water regardless of its polarity, unless that particle is polar and made up of several atmos with different polarities.  So basically, the particle won't separate out into different atoms when you place it in water.  It has no charge because of this.
Ergo, it won't be repelled by the hydrophilic head, because it has no charge.  It just LOVES LIPIDS, hence the name, so it can be drawn through the layer and out the other side presumably by standard diffusion.

So let's break it down a little more easily.

A hydrophilic head and a hydrophobic tail are repelled by or attracted to water (not each other!)
So when the particle approaches the hydrophilic head, the particle clearly isn't water and it isn't dissolved in water.  It has no charge so it can't be repelled by the polar head.
It has no charge so it won't be affected by the head or the tail.  Therefore, the hydrophilic head won't repel the particle and neither will the hydrophobic tail.  In fact, the hydrophobic tail is the same polarity as the particle, just as the hydrophilic head is the same polarity as water.  Therefore, the particle is considered lipophilic as it loves the lipid of the membrane just as the hydrophilic head loves the water in the surrounding fluid.  The fact that it passes through the head is irrelevant; the head is still a lipid, and it'll let the particle pass through because the particle has no charge.  The head can't repel something with no charge.

My explanation skills when it comes to biology are now a little rusty but for the purposes of this question I hope I have sorted out any possible flaw you can see in the theory.