VCE Biology Question Thread

[RazzMeTazz]

Is it the cholesterol in plasma membranes that allow for the membrane to reseal itself if it is punctured?

[howlingwisdom]

How would you identify a neurohormone from a neurotransmitter?

Are all neurotransmitters proteins?

[katiesaliba]

Is it the cholesterol in plasma membranes that allow for the membrane to reseal itself if it is punctured?

Cholesterol assists membranes in maintaining their structure, so yes it would help. The hydrophobic attractions between the tails of phospholipids, however, will provide membranes with the means for repairing themselves. Just think about the polarity of a phospholipid and the hydrophobic and hydrophilic ends. 

[RazzMeTazz]

Does cholesterol increase or decrease the fluidity of membranes?

In some sources I have come across, it says cholesterol increases the fluidity of membranes but others say they add a level of rigidity to membranes?

Does anyone know which is actually correct?
o.O

[howlingwisdom]

Does cholesterol increase or decrease the fluidity of membranes?

In some sources I have come across, it says cholesterol increases the fluidity of membranes but others say they add a level of rigidity to membranes?

Does anyone know which is actually correct?
o.O

Cholesterol actually increases or decreases fluidity depending on the temperature!

At low temperatures, the cholesterol will make the phosphilipid bilayer more fluid in order to prevent solidification, whereas at high/moderate temperatures, the cholesterol will reduce the membrane's fluidity.

[alondouek]

Does cholesterol increase or decrease the fluidity of membranes?

In some sources I have come across, it says cholesterol increases the fluidity of membranes but others say they add a level of rigidity to membranes?

Does anyone know which is actually correct?
o.O

It's actually both, funnily enough. Cholesterol serves to give the membranes both fluidity and rigidity in different conditions. It is a 'bidirectional regulator' of membrane fluidity.

When environmental temperature is high, cholesterol gives the membrane rigidity by raising the membrane's melting temperature, while at low temps it acts to prevent the membrane from stiffening and becoming too rigid.

edit: beaten by howlingwisdom haha

[Frozone]

What is the purpose of the NAD+ molecule?

[alchemy]

What is the purpose of the NAD+ molecule?

It's an unloaded carrier molecule. It is loaded with H to form NADH. NADH is then unloaded to form ATP in the electron transport chain, releasing NAD+ back for reuse. 

[RazzMeTazz]

It's actually both, funnily enough. Cholesterol serves to give the membranes both fluidity and rigidity in different conditions. It is a 'bidirectional regulator' of membrane fluidity.

When environmental temperature is high, cholesterol gives the membrane rigidity by raising the membrane's melting temperature, while at low temps it acts to prevent the membrane from stiffening and becoming too rigid.

edit: beaten by howlingwisdom haha

Thanks for clearing up my confusion!
I really appreciate it!

[RazzMeTazz]

Cholesterol actually increases or decreases fluidity depending on the temperature!

At low temperatures, the cholesterol will make the phosphilipid bilayer more fluid in order to prevent solidification, whereas at high/moderate temperatures, the cholesterol will reduce the membrane's fluidity.

Oh thanks so much!!
Great explanation!

[eagles]

Are lysosomes present in plant cells?

I thought that they may have because since the cell wall is fully permeable, heaps of foreign matter can enter the cell.
To remove the foreign matter, lysosomes play an important role in digesting them.

Can I have some feedback about this?

[alchemy]

Are lysosomes present in plant cells?

I thought that they may have because since the cell wall is fully permeable, heaps of foreign matter can enter the cell.
To remove the foreign matter, lysosomes play an important role in digesting them.

Can I have some feedback about this?

That's been a long debated topic, but current evidence does suggest that they have lysosomes. 

[Scooby]

Are lysosomes present in plant cells?

I thought that they may have because since the cell wall is fully permeable, heaps of foreign matter can enter the cell.
To remove the foreign matter, lysosomes play an important role in digesting them.

Can I have some feedback about this?

It's debated, but I'd just go with the notion that they don't for VCE. Either way, plant cell vacuoles also contain hydrolytic enzymes capable of digesting cellular debris and other materials

And a plant cell wall may be completely permeable - but remember that plant cells are also bound by a cell plasma membrane, which is selectively permeable, so not everything just floats into and out of the cell

[alchemy]

I was wondering about the fate of the NADH molecules in anaerobic respiration. When the net 2 ATP is produced, and NAD becomes loaded to NADH, what happens to the NADH after that. Surely, they can't get unloaded right, because there's no more ATP produced in that process?

[nhmn0301]

I was wondering about the fate of the NADH molecules in anaerobic respiration. When the net 2 ATP is produced, and NAD becomes loaded to NADH, what happens to the NADH after that. Surely, they can't get unloaded right, because there's no more ATP produced in that process?

I think this question is out of VCE scope but if you are interested, NADH during anaerobic respiration actually can get converted back into NAD to produce lactic acid (in human) and ethanol (in plants). The way they do it in human is to make NADH undergoes oxidation reaction, eventually donates it H+ ion to the pyruvate in glycolysis to from something called lactate, then with the help of an enzyme called lactase dehydrogenase, contributes to the production of Lactic acid. In plants, NADH undergoes oxidation reaction as well, donates its H+ ion to pyruvate just like in human, but the only difference is the enzyme that involve in this process, called decarboxylase, helping plants to produce ethanol in the end.
Hope this helps!