VCE Biology Question Thread

[kurdish123]

Hey everyone:)
Can anyone tell me how I can attach files onto this thread?

[Photon]

Thank you guys 

1. Detergents are tricky to explain, because they're really similar to phospholipids. Basically though, the key difference between detergents and phospholipids is that detergents like to form balls, whereas phospholipids prefer to form bilayers. Not going to go into why that's the case, other than to say it has to do with the shape of the molecules.

(Image removed from quote.)

What detergents basically do is bind fats by their hydrophobic tail and bind water by the hydrophilic head, much like phospholipids. This allows them to form balls called micelles that dissolve in water (because the heads are on the outside of the micelle) and that store lipids in their core. This is what they do to fats, what they do to phospholipids is much the same and is shown above. Rather than the phospholipid being stored in the core of the micelle, it is stored in the micelle itself, substituting a detergent molecule.

If this doesn't make sense, don't worry about it too much—it's beyond VCE. Just know that they can disrupt fat droplets and bilayers and you're sweet.

2. A true point. Tertiary structure gives the toplogy of the molecule, its functional shape as it were. So tertiary structure describes how all of the secondary structures fold into each other to make a particular shape.

3. Membrane proteins (genuinely what they're called technically)

4. Each level of structure is a distinct unit. So secondary structure, for instance, doesn't include the peptide bonds between amino acids. That is the protein's primary structure. So secondary structure doesn't describe a state that the protein is in, it describes some of the elements of the protein's structure.

If that doesn't make sense, think of it this way. A protein simultaneously has primary, secondary and tertiary structure. Its primary structure is the order of amino acids (linked by peptide/amide bonds), its secondary structure arises from hydrogen bonding between hte peptide backchain forming alpha-helices, beta-sheets and random coils and its tertiary structure is the overall topology of the protein, formed by a host of interactions between R-groups, including salt bridges, hydrogen bonds, disulphide bridges etc etc.


Nuclear membranes are double folded, whereas plasma membranes aren't. Google some images, will make sense

You said that the reason why detergent dissolves in water is because it has a hydrophilic head and hydrophobic tails. Then why is it that our phospholipids are not the same as they also have hydrophilic heads and hydrophobic tails? Could it be because they don't form micelles? If so, then why do detergents form miscelles in the first place?

[Photon]

Hey everyone:)
Can anyone tell me how I can attach files onto this thread?

Once you go into preview mode you click on "Attachments and other options" and then "browse". Then choose your file from there.

[vox nihili]

Thank you guys 

You said that the reason why detergent dissolves in water is because it has a hydrophilic head and hydrophobic tails. Then why is it that our phospholipids are not the same as they also have hydrophilic heads and hydrophobic tails? Could it be because they don't form micelles? If so, then why do detergents form miscelles in the first place?

Way beyond VCE

Absolutely don't need to know this, but it has to do with the shape of the molecule.

If you look at a phospholipid, the head of the phospholipid has the same cross-sectional area as the fatty acid tail. In other words, the phospholipid is kind of like cylinder shape. Detergents, on the other hand, are a bit different. The cross-sectional area of the hydrophilic head is greater than the cross-sectional area of the tail. As such, detergents are cone-shaped.

Now that's all well and good, but what does it mean? Well it means that phospholipids like to pack in together in parallel. In other words, they like to line up in a line. Therefore, make a membrane, wherein all the heads can be in water and the tails in lipid, they form a bilayer.
Detergents, on the other hand, like to line up with each other, however, they can't really fit in together side-by-side. So rather than lining up in a straight line, they line up in a line that curves (in 2D, obviously these are actually 3D in real-life). As such, to make sure all the tails are with lipids and the heads in water, they're better to just form tight balls rather than a bilayer membrane.

I appreciate that that's all pretty confusing, so if you're completely lost just ignore what I've said and have a look at the image I've attached. You can see that the shapes of the molecules are different and, as a consequence, they pack in together differently.

[Photon]

Way beyond VCE

Absolutely don't need to know this, but it has to do with the shape of the molecule.

If you look at a phospholipid, the head of the phospholipid has the same cross-sectional area as the fatty acid tail. In other words, the phospholipid is kind of like cylinder shape. Detergents, on the other hand, are a bit different. The cross-sectional area of the hydrophilic head is greater than the cross-sectional area of the tail. As such, detergents are cone-shaped.

Now that's all well and good, but what does it mean? Well it means that phospholipids like to pack in together in parallel. In other words, they like to line up in a line. Therefore, make a membrane, wherein all the heads can be in water and the tails in lipid, they form a bilayer.
Detergents, on the other hand, like to line up with each other, however, they can't really fit in together side-by-side. So rather than lining up in a straight line, they line up in a line that curves (in 2D, obviously these are actually 3D in real-life). As such, to make sure all the tails are with lipids and the heads in water, they're better to just form tight balls rather than a bilayer membrane.

I appreciate that that's all pretty confusing, so if you're completely lost just ignore what I've said and have a look at the image I've attached. You can see that the shapes of the molecules are different and, as a consequence, they pack in together differently.

(Image removed from quote.)

Wow, I actually get it now. Thank you so much Mr T-Rav! You've been a great help   

[vox nihili]

Wow, I actually get it now. Thank you so much Mr T-Rav! You've been a great help   

No worries

It's actually really cool stuff, weirdly. We had to learn about them last year and how they're used to study membrane proteins, and that was really cool. Turns out there's a lot to know about detergents!

[gameboy99]

Hey guys, I'm in yr11 doing Bio and I was thinking of doing questions from past VCAA papers from what I have learnt so far in Biology this year. Should I leave some papers for later in the year so I can do them under timed conditions or is it better to do questions with all the VCAA papers???
ALSO, what are the most recommended company papers I should do???

[cosine]

Hey guys, I'm in yr11 doing Bio and I was thinking of doing questions from past VCAA papers from what I have learnt so far in Biology this year. Should I leave some papers for later in the year so I can do them under timed conditions or is it better to do questions with all the VCAA papers???
ALSO, what are the most recommended company papers I should do???

I really encourage you to save at least 2010-2015 exam papers for like a month before the actual exam, just because it will really refresh you and and can be seen as an indicator as to how you will perform on the exam. I did the 2014 exam like a week before my actual exam and it had so many similarities to our own exam, so everything I learnt from the 2014 was still fresh and etc.

I did the <2010 (1998/2009) exams like three/four months before the end of year exam. So you really don't have to do them the early, my main worry that you will run out of good exam questions, because many biology company papers are not reliable, leading to your next question, the best exam papers are VCAA, 100%. NEAP was pretty good but they go beyond VCE, so only do them if you're really confident.

[Gogo14]

Why do lipophilic/ hydrophobic molecules pass through the membrane? Wouldnt they just stay in the fatty acid tails instead of passing through to intracellular fluid?

[Photon]

Why is it that all amphipathic molecules make lipids soluble?

[qwertyqwerty]

Why is it that all amphipathic molecules make lipids soluble?

I'm assuming you mean soluble in water. A micelle is formed with the molecule and the lipid. The hydrophobic part of the molecule faces inside the micelle, while the hydrophilic part sticks out. Because of this, it is able to dissolve in water.

[gameboy99]

Is it useful doing quick check, and chapter review questions from Nature of Biology because most questions are pretty easy... is it also useful doing most of biozone???

[vox nihili]

Why is it that all amphipathic molecules make lipids soluble?

They don't necessarily, but the details of that are probably a little complex to go into here Better to not worry all that much about detergent

[Photon]

I'm assuming you mean soluble in water. A micelle is formed with the molecule and the lipid. The hydrophobic part of the molecule faces inside the micelle, while the hydrophilic part sticks out. Because of this, it is able to dissolve in water.

How would that be different from a phospholipid bilayer? Phospholipids bilayer are practically the same thing except they don't form miscelles because of their shape

[vox nihili]

How would that be different from a phospholipid bilayer? Phospholipids bilayer are practically the same thing except they don't form miscelles because of their shape

Well some lipids are dissolved in the phospholipid bilayer, such as cholesterol for instance.