VCE Biology Question Thread

[Stick]

What is the point of the DNA strands found in chloroplasts?

The reactions that make up photosynthesis are all dependent on enzymes. As you should already know, enzymes are a type of protein. In some cases, we're going to need protein synthesis to occur rather rapidly in order to keep up normal function. If we relied on nuclear DNA, it'd be a rather inefficient pathway - the DNA would be transcribed in the nucleus, the messenger RNA would have to exit the nucleus and approach a ribosome somewhere in the cytoplasm to be translated and the new protein would then have to be transported through the endoplasmic reticulum to the chloroplast before it could be used to catalyse important photosynthetic reactions. As you can see, having the DNA (and ribosomes) where the resulting protein will be used is very handy - protein synthesis occurs in the chloroplast rather than somewhere else in the cell and it can be used as soon as translation has concluded.

[DJA]

Thanks for all the answers guys. Really consolidating my learning.

And on a side note congrats on your 2500th post stick

[alchemy]

A bit late to the party here, but I'll try ask some questions while I can.

Biocatalysis is also important because organisms only have a certain amount of energy that they can devote to biological reaction systems, which means that by lowering the required energy input for vital biochemical reactions, the organism's energy input (such as food) can be reduced.

Can you please explain this again? Lower input=lower input?

Lysosomes are basically membrane-bound sacs that contain digestive enzymes called lysosymes. These lysozymes are secreted, the lysozymes break down the matter taken up by the cell, and the lysozyme, an enzyme, is neither used up nor consumed by this catabolic reaction. So essentially, no, the lysosomes are not destroyed in this instant.

So when lysosomes ‘recycle’ mitochondria they aren’t destroyed in that process as well, right? What happens to these hydrolytic enzymes (lysozymes) once they’ve done their job of recycling? Also, why would an organelle, such as mitochondria, be recycled by these enzymes?   

[psyxwar]

A bit late to the party here, but I'll try ask some questions while I can.

Can you please explain this again? Lower input=lower input?

needing less energy to drive metabolism = animal does not need to eat as much to survive

[vox nihili]

So when lysosomes ‘recycle’ mitochondria they aren’t destroyed in that process as well, right? What happens to these hydrolytic enzymes (lysozymes) once they’ve done their job of recycling? Also, why would an organelle, such as mitochondria, be recycled by these enzymes?

Whether or not the lysosomes are destroyed is irrelevant really. In some instances their membranes will be completely voided (so yes, destroyed), others not so much. Mitochondria are recycled because they get, for want of a better way to explain it, get tired and a bit buggered essentially. Like anything, there's wear and tear on the mitochondria, so they need to be replaced.
The enzymes themselves may very well be broken down, or go onto recycling more things. Quite often they will be broken down though, or can be degraded or deactivated by other cell processes. They're all very nitpicky questions, particular about what happens with the enzymes and I daresay there's are questions we don't really yet have definitive answers to.

[Frozone]

What is the difference between carrier mediated protein channels and channel mediated protein channels in the phospholipid bilayer of the plasma membrane?? (i do know that they both do not require energy...but thats it)

And I am not referring to the active transport carrier protein where energy is required to carry substances through the plasma membrane.

Edit: The diagram I am pondering over and not understanding is on pg 44 of the Nature of Biology TB if anyone has that text.
(3 types of passive transport: Simple diffusion, Channel mediated, Carrier mediated: the last two I do not get the difference)

My book says nothing about channel mediated and carrier mediated. Should I be worried. By the way I'm using heinenman biology 2.

[vox nihili]

My book says nothing about channel mediated and carrier mediated. Should I be worried. By the way I'm using heinenman biology 2.

It may not use those exact terms. Mine (Nelson) just called them channel proteins and carrier proteins. yes you do need to know the difference.

[DJA]

Do we need to know about the induced fit model for enzymes? Or do we just need to know the lock and key model?

[grannysmith]

I'm led to believe that carrier proteins, although used in diffusion, can also be used in active transport?

[Stick]

Do we need to know about the induced fit model for enzymes? Or do we just need to know the lock and key model?

It's not a bad idea to know both.

I'm led to believe that carrier proteins, although used in diffusion, can also be used in active transport?

Yep, you're correct! It's the only way active transport occurs.

[grannysmith]

Do we need to know about the induced fit model for enzymes? Or do we just need to know the lock and key model?

I think they're both models (theories if you like), and neither have been proven or disproved. One states that the active site is the exact complementary shape of the substrate, whereas the other one says that the enzyme "fits" itself around the substrate.

Edited

[vox nihili]

I think they're both models (theories if you like), and neither have been proven or disproved. One states that the active site is the exact shape of the substrate, whereas the other one says that the enzyme "fits" itself around the substrate.

Induced fit is supported by much more research than lock and key. Lock and key is presented as a way to introduce the theory, whereas induced fit is somewhat of an intellectual expansion on that, and is more correct. So technically, you learn the incorrect model first because it's easier, and then get corrected by induced fit. Nonetheless, lock and key does pop up often and is essentially right as a model.

[grannysmith]

Induced fit is supported by much more research than lock and key. Lock and key is presented as a way to introduce the theory, whereas induced fit is somewhat of an intellectual expansion on that, and is more correct. So technically, you learn the incorrect model first because it's easier, and then get corrected by induced fit. Nonetheless, lock and key does pop up often and is essentially right as a model.

So I'm guessing for the purpose of VCE biology, both models are essentially correct?

[grannysmith]

It's not a bad idea to know both.

Yep, you're correct! It's the only way active transport occurs.

Cool!

[alchemy]

I'm led to believe that carrier proteins, although used in diffusion, can also be used in active transport?

Just remember that active transport is for the movement of substances across the membrane, via carrier proteins and through protein channels, against the concentration gradient.