VCE Biology Question Thread

[Corey King]

Hey guys,
We learned that lipids in the plasma membrane are hydrophobic.
I thought this might have meant that they were neutral to water, but apparently it can be repelled by as well.

What I dont get is how something is repelled by water?

Im imagining a hydrocarbon chain. No real polarity. Won't the hydrocarbon and water just ignore each other?

Many thanks,
Corey

Additionally,

 Does active transport always require that there be a higher or equal concentration of the transported substance on the side of the cell being transported to. What if a nonpolar and large substance needs to cross the plasma membrane, but it is in higher concentration on the outside of the cell? Is this passive?

-Does the DNA create membrane proteins and cholesterol? How are they formed?

-If an amphipathic molecule has two parts with different polarities, does this mean that any hydrocarbon chain with only one functional group is amphipathic?
Sorry for the bombardment, my teacher was sick this week

My research says that a peripheral protein is that which doesnt enter the hydrophic element of the bi-layer.

However, when I google a peripheral protein, I get images like the one attached.

This seems to clearly penetrate the lipids to me.

Would the peripheral protein look more like this? (second attachment)

Mod edit: I've merged your posts into one. Please use the 'modify' button to edit your post instead of posting in succession -owlbird83

[Coolmate]

Hey guys,
We learned that lipids in the plasma membrane are hydrophobic.
I thought this might have meant that they were neutral to water, but apparently it can be repelled by as well.

What I dont get is how something is repelled by water?

Im imagining a hydrocarbon chain. No real polarity. Won't the hydrocarbon and water just ignore each other?

Many thanks,
Corey

Hey Corey!
While I didn't do VCE Biology, I have provided some information that may help with your question

Hydrophobic = A molecule that has a tendency to repel water
- A molecule is hydrophobic due to its chemical properties/ structure

Hydrophilic = A molecule that is attracted to water

A common example of Hydrophobia is water and oil. When you put water into a bowl of oil, the oil will repel the water. This is because water molecules have one oxygen atom and two hydrogen atoms, whereas oil is composed of Triglycerides (Lipids), hence has a polarity of non-polar (it is not attracted to the polarity of water).

^I think this would be the same for the Hydrocarbon

On the other hand, a polar molecule attracted to water is sugar. This is because sugar is "water loving", thus attracted to the water.

This article goes into the electrostatics of polar molecules.

I hope this helps!
Coolmate

[Corey King]

Hey Corey!
While I didn't do VCE Biology, I have provided some information that may help with your question

Hydrophobic = A molecule that has a tendency to repel water
- A molecule is hydrophobic due to its chemical properties/ structure

Hydrophilic = A molecule that is attracted to water

A common example of Hydrophobia is water and oil. When you put water into a bowl of oil, the oil will repel the water. This is because water molecules have one oxygen atom and two hydrogen atoms, whereas oil is composed of Triglycerides (Lipids), hence has a polarity of non-polar (it is not attracted to the polarity of water).

^I think this would be the same for the Hydrocarbon

On the other hand, a polar molecule attracted to water is sugar. This is because sugar is "water loving", thus attracted to the water.

This article goes into the electrostatics of polar molecules.

I hope this helps!
Coolmate

Hey Coolmate, I know that the heads are hydrophilic and tails hydrophobic. What I do get is that the heads are polar and so create hydrogen bonds with the surrounding water.

What I dont get is what forces are in play that makes the lipid tails attrated to each other, and what makes them repulsed from polar molecules.

The article you listed says the hydrophobic molecules actually just collect together because they are not attracted to anything.

If so, why does the bi-layer not just pull apart as the heads are pulled in the direction of the water?

[Sine]

-snip-

You really don't need to go into this much detail with regards to the chemical forces at play but I'll try to answer your q's.

Lipid tails attract to each other as a result of the absence of the attraction to water. Phospholipids form into a bi-layer since it is the most energetically favourable structure that the phospholipids can form. Depending on the shape of the lipids also micelles/liposomes can be formed.

The bi-layer and liposomes are more for cylindrical shaped diglycerides whereas cone-shaped monoglycerides tend to form liposomes/micelles. 

[Chocolatepistachio]

if someone could help with this question wouldn't it be c

[Owlbird83]

if someone could help with this question wouldn't it be c

yes c!
An action potential is when the electrical signal moves along the neuron. Is does this through the (normally closed) Na+ ion channels opening and letting in Na+ ions into the axon which causes channels next to it open and results in the wave (of opening channels and entering Na+ ions) that travels along the axon. It would be c because that's where the positive ions are currently being let in.

Does active transport always require that there be a higher or equal concentration of the transported substance on the side of the cell being transported to. What if a nonpolar and large substance needs to cross the plasma membrane, but it is in higher concentration on the outside of the cell? Is this passive?

If it's travelling against concentration gradient it will require energy/ be active transport.
If the molecule is large if might need to travel though a channel/carrier protein, will still only be passive if moving with concentration gradient (facilitated diffusion), and active if going to area of higher conc. .

-Does the DNA create membrane proteins and cholesterol? How are they formed?

I'm not too sure on cholesterol, but membrane proteins are created from transcription of DNA then translation of mRNA in the cell (+further modifications/folding ).

-If an amphipathic molecule has two parts with different polarities, does this mean that any hydrocarbon chain with only one functional group is amphipathic?

I think if the functional group was polar, then yes. But if the one functional group was non-polar, then no.

My research says that a peripheral protein is that which doesnt enter the hydrophic element of the bi-layer.

However, when I google a peripheral protein, I get images like the one attached.

Not too sure on this sorry. I googled too and got the same thing. Maybe it depends on the specific type of peripheral protein and some just hang a bit more in?

[-Lilac-]

-Does the DNA create membrane proteins and cholesterol? How are they formed?

Owlbird83 covered this well but I'll just add on a little regarding cholesterol (not VCE knowledge though). Cholesterol is created via a biosynthesis pathway involving many different enzymes. So while the Cholesterol itself is not encoded by DNA, the enzymes involved in the series of reactions that coverts acetyl- CoA into Cholersteol are proteins and therefore are transcribed/translated.

[Corey King]

Hey
Here in Biozone it says exocytosis is used to export large polar molecules. Why don't we just excrete them through facilitated diffusion? Also, why only get rid of large polar molecules this way? It seems like a good way to get rid of bulk molecules of any kind .
Thank you,
Corey

[lm21074]

I'm doing 3&4 bio this year, so someone please correct me if I'm wrong!

Facilitated diffusion involves the passive diffusion of small charged or polar molecules from an area of high concentration to an area of low concentration across a semi-permeable membrane through protein channels or carrier proteins.

Exocytosis is a type of bulk transport - movement of large substances in and out of the cell. Therefore, because they are too big, these large substances cannot move through carrier proteins or protein channels. Rather, they have to move by being packaged into vesicles and fusing with the plasma membrane because they are such large molecules. In order to package and move such large material out of the cell via exocytosis, ATP is required, and facilitated diffusion is not an ATP-requiring process. It is also more efficient for the cell to undergo this process as it is used when a cell needs to release a large amount of substance quickly (e.g. hormones) out of the cell.

Hope this helps you out a bit

[Chocolatepistachio]

For this question

Lupus is a disease in which the immune system makes antibodies that attack the persons own connective tissues targeting them for destruction by the immune system. Which of the following might be a useful drug therapy for lupus?
A a drug that inhibits function(s) of cytotoxic T cells
B a drug that inhibits all cytokines
C a drug that inhibits the function(s) of B cells
D a drug that inhibits phagocytosis by macrophages

Would this be a

[-Lilac-]

For this question

Lupus is a disease in which the immune system makes antibodies that attack the persons own connective tissues targeting them for destruction by the immune system. Which of the following might be a useful drug therapy for lupus?
A a drug that inhibits function(s) of cytotoxic T cells
B a drug that inhibits all cytokines
C a drug that inhibits the function(s) of B cells
D a drug that inhibits phagocytosis by macrophages

Would this be a

The key to this question is the mention of antibodies. This indicates to us that Lupus is a B cell-mediated autoimmune disease as those are the cells that produce the antibodies. Thus, C would be the correct answer.

[Chocolatepistachio]

Thanks

If someone could help with this question

A viral infection can give rise to a phenomenon called ‘ cytokine storm’. What is a cytokine storm and how does it affect an individual infected with the virus?
A cytokine storm is the phenomenon by which the infecting virus releases multiple cytokines. These cytokines enable the virus to infect more host cells and make more viruses
B cytokine storm is the phenomenon by which the host immune system overreacts  to a viral infection and produces large amounts of multiple cytokines. These cytokines enable the host to produce more viruses which then attack host organs
C cytokine storm is the phenomenon by which the host immune system overreacts to a viral infection and produces large amounts of multiple cytokines. These cytokines not only attack the virus but also attack host organs resulting in organ failure and sometimes death
D cytokine storm is the phenomenon by which the infecting virus releases multiple cytokines. These cytokines then attack host cells and organs and sometimes can lead to the death of an individual

[Erutepa]

Thanks

If someone could help with this question

A viral infection can give rise to a phenomenon called ‘ cytokine storm’. What is a cytokine storm and how does it affect an individual infected with the virus?
A cytokine storm is the phenomenon by which the infecting virus releases multiple cytokines. These cytokines enable the virus to infect more host cells and make more viruses
B cytokine storm is the phenomenon by which the host immune system overreacts  to a viral infection and produces large amounts of multiple cytokines. These cytokines enable the host to produce more viruses which then attack host organs
C cytokine storm is the phenomenon by which the host immune system overreacts to a viral infection and produces large amounts of multiple cytokines. These cytokines not only attack the virus but also attack host organs resulting in organ failure and sometimes death
D cytokine storm is the phenomenon by which the infecting virus releases multiple cytokines. These cytokines then attack host cells and organs and sometimes can lead to the death of an individual

For this question you need to understand that cytokines are (as VCAA puts it) 'signalling molecules within the immune system'. They are a very broad category of molecules which our immune cells produce and secrete to carry out many different immune system functions. Knowing this we can immediately eliminate A and D which suggest the virus releases cytokines as this in incorrect - our immune cells produce them.

Left with B and C, knowing that cytokines function to aid in the functioning of out immune cells, we can eliminate B which states that the cytokines are aiding in viral replication. Instead C describes a situation where the cytokines are acting to aid the function of the immune system by targeting the viral pathogen (as well as damaging self cells due to the excessive production of cytokines).

Hopefully this makes sense, however feel free to point out anything i might not have explained well

[jm08]

Hi,

I have a prac test SAC in next month and I was wondering what we had to do for it. Is it like a test on a prac we do in class or will we have to write up a report (aim, discussion etc.)?

[lm21074]

Hi,

I have a prac test SAC in next month and I was wondering what we had to do for it. Is it like a test on a prac we do in class or will we have to write up a report (aim, discussion etc.)?

This is something you should check with your teacher, as every school designs their SACs differently