Bio 3&4 Questions!!

[Scooby]

Water diffuses across the phospholipid bilayer via aquaporins, yeah? Would this be a type of simple diffusion or facilitated diffusion?

Why aren't non-polar molecules repelled by the hydrophilic head of a phospholipid?

Is the sodium-potassium pump a type of uniporter or antiporter?

Are monosaccharides and disaccharides soluble?

Thanks guys

[Panicmode]

Water diffuses across the phospholipid bilayer via aquaporins, yeah? Would this be a type of simple diffusion or facilitated diffusion?

Why aren't non-polar molecules repelled by the hydrophilic head of a phospholipid?

Is the sodium-potassium pump a type of uniporter or antiporter?

Are monosaccharides and disaccharides soluble?

Thanks guys

1. Okay, water diffusing across a plasma membrane is given a special name (since it is the solvent and not the solutt moving) called osmosis. Technically, since it uses a protein channel (aquaporin) it is a type of facilitated diffusion, but you will never see it called that. It will almost always be referred to as osmosis.

2. Non-polar molecules aren't repelled because they don't have a charge. The fact that they are non-polar just means that they can't mix well with polar molecules because the strongest forces holding them together would be van der Waals. So it's not so much that they are repelled, more so that they can't mix well. It isn't the same kind of repulsion as you would expect say two negatively charged molecules to have for each other.

3. An antiporter as it pumps in potassium ions at the same time as pumping out sodium ions.

4. Yes. Sucrose (table sugar) is an example of a disaccharide and as you know, it is fairly soluble in water.

[Scooby]

Cool. Thanks Panicmode!

[Scooby]

Just a few more questions...

If non-polar molecules aren't repelled by the hydrophilic heads, why are polar molecules like water repelled by the hydrophobic tails?

When we say disaccharides are 'soluble' in water, does that just mean it will split into its monosaccharides in water?

How can a monosaccharide be soluble in water if it is only a single molecule?

[Panicmode]

Just a few more questions...

If non-polar molecules aren't repelled by the hydrophilic heads, why are polar molecules like water repelled by the hydrophobic tails?

When we say disaccharides are 'soluble' in water, does that just mean it will split into its monosaccharides in water?

How can a monosaccharide be soluble in water if it is only a single molecule?

1. It will not pass through the plasma membrane because it cannot "dissolve" in the plasma membrane.

2 / 3. No, disaccharides contain many hydroxy (OH) groups. This allows them to form hydrogen bonds with water and so dissolve in water. Similarly, monosaccharides are soluble in water because of their ability to form hydrogen bonds.

[blank]

1/ I'm confused about the differences in terms of properties (e.g. elasticity etc) b/w alpha helices & beta sheets. My teacher said that alpha helices are stretchy and my textbook says that beta sheets give silk tensile strength but are less rigid than alpha helices so they can form enzyme active sites. Doen't less rigid mean more elastic? So then how can it be strong?

2/ What is the difference b/w the functions of glycolipids and glycoproteins?

3/ Do glucose molecules pass the plasma membrane by faciltated diffusion or active transport?

4/ How do the molecules that use carrier proteins differ from those that use channel proteins to pass the membrane?

5/ Is there such thing as active diffusion?

Thanks! (totally lost :S)

[nubs]

Really testing my memory here (may not be entirely accurate)

2: (I wouldn't worry too much about this, just know what they look like, what they're made of and where they are found - that should be enough) But here you are anyway
http://au.answers.yahoo.com/question/index?qid=20100128212701AA4IWHQ

3: Facilitated diffusion

4: The ones that use carrier proteins are 'carried' by specific proteins across the membrane. For the other ones, the protein channels just open up and let the particular molecules pass through

5: I have never come across the term 'active diffusion' before and I can't find anything suggesting that such a thing exists after a quick google search.

[Scooby]

1. It will not pass through the plasma membrane because it cannot "dissolve" in the plasma membrane.

2 / 3. No, disaccharides contain many hydroxy (OH) groups. This allows them to form hydrogen bonds with water and so dissolve in water. Similarly, monosaccharides are soluble in water because of their ability to form hydrogen bonds.

Alrightyy

1. So why can't water undergo simple diffusion? Isn't it already small enough to diffuse through the bilayer?

2. Ohhh, okay. So why can't polysaccharides dissolve in water?

[Panicmode]

1. It will not pass through the plasma membrane because it cannot "dissolve" in the plasma membrane.

2 / 3. No, disaccharides contain many hydroxy (OH) groups. This allows them to form hydrogen bonds with water and so dissolve in water. Similarly, monosaccharides are soluble in water because of their ability to form hydrogen bonds.

Alrightyy

1. So why can't water undergo simple diffusion? Isn't it already small enough to diffuse through the bilayer?

2. Ohhh, okay. So why can't polysaccharides dissolve in water?

1) Yes.

2) Polysaccharides can't dissolve in water because they are much larger than their monosaccharide monomers. As the chain gets bigger and bigger, the solubility in water decreases. Even though they may be able to form hydrogen bonds with surrounding water molecules, their affinity for themselves is much greater than their affinity for the surrounding solution and so they will not dissolve.