VCE Biology Question Thread

[johnhalo]

Hey guys,

I was just going over cellular respiration/photosynthesis, and just had a question:

How does the ATP produced during cellular respiration break down into ADP + Pi in order to release energy which drives all the functions in our body?

I remember reading somewhere that ATP acts as a coenzyme and it is through an enzyme reaction that it turns into ADP + Pi, but I just wanted to make sure.

Thanks

[vox nihili]

Wow, I did not expect this to happen. The truth is that I had a multiple choice question asking how starch passes through the membrane and I answered endocytosis when some other classmates answered channel proteins. We still don't know who's right and I was hoping I could resolve it by asking here but I got both answers. :l

My guess is that it gets broken down via hydrolysis reactions into glucose and then transported only to be 'rebuilt' on the the other side of the membrane.

I'm not really sure about starch, but glycogen is certainly transported via being broken down and remade in cells, as I suggested earlier. Theoretically, however, starch could be transported by exocytosis/endocytosis, though there is really no reason at all to do so. Channel proteins are most certainly wrong though. The channels can't be that big.

Hey guys,

I was just going over cellular respiration/photosynthesis, and just had a question:

How does the ATP produced during cellular respiration break down into ADP + Pi in order to release energy which drives all the functions in our body?

I remember reading somewhere that ATP acts as a coenzyme and it is through an enzyme reaction that it turns into ADP + Pi, but I just wanted to make sure.

Thanks

This is a good way of looking at it. It's a little more complicated than that, but getting bogged down in the details will only confuse everyone, including me!

[cosine]

Wow, I did not expect this to happen. The truth is that I had a multiple choice question asking how starch passes through the membrane and I answered endocytosis when some other classmates answered channel proteins. We still don't know who's right and I was hoping I could resolve it by asking here but I got both answers. :l

My guess is that it gets broken down via hydrolysis reactions into glucose and then transported only to be 'rebuilt' on the the other side of the membrane.

If we are talking VCE Biology, your answer is correct. Starch will be transported via endocytosis, it cannot go through channel proteins, as only polar, and relatively smaller (comparing to starch) molecules can actually go through channel proteins, because there is a polar lining inside the channel proteins, so starch is not only too large, it is non-polar so it cannot go through the channel protein.

[Splash-Tackle-Flail]

Quick question, when something like a glucose solution is infused in the body, and travels in the bloodstream, can the glucose molecules diffuse into the red blood cells via protein channels? If they don't (i.e. and instead enter interstitial fluid and enter other cells such as tissue cells), how to red blood cells get energy? (i.e. can glucose metabolise outside of a cell so that it's broken down products can enter the red blood cell??)

Thanks in advance

[cosine]

Quick question, when something like a glucose solution is infused in the body, and travels in the bloodstream, can the glucose molecules diffuse into the red blood cells via protein channels? If they don't (i.e. and instead enter interstitial fluid and enter other cells such as tissue cells), how to red blood cells get energy? (i.e. can glucose metabolise outside of a cell so that it's broken down products can enter the red blood cell??)

Thanks in advance

Yes, glucose molecules can diffuse through the protein channels of cells if the concentration is higher on the outside of the cell (interstitial fluids), than it is inside. And to your second question, no, anaerobic and aerobic respiration occurs in the cytoplasm inside of cells, glucose does not get broken down outside the cells.

[Splash-Tackle-Flail]

Yes, glucose molecules can diffuse through the protein channels of cells if the concentration is higher on the outside of the cell (interstitial fluids), than it is inside. And to your second question, no, anaerobic and aerobic respiration occurs in the cytoplasm inside of cells, glucose does not get broken down outside the cells.

So there are protein channels for glucose in red blood cells? It's just that a friend told me glucose metabolises outside the cell for red blood cells, but in the cytoplasm for other cells.

Dude, you're literally a beast at bio- like please come host a lecture for me

[cosine]

So there are protein channels for glucose in red blood cells? It's just that a friend told me glucose metabolises outside the cell for red blood cells, but in the cytoplasm for other cells.

Dude, you're literally a beast at bio- like please come host a lecture for me

Okay so I may go into too much detail here, so beware. Red blood cells (of humans) are enucleated, that is, they do not have a nucleus. These cells lose their nucleus and so they do not have the genetic code (DNA) to synthesise the proteins that are required for the production of the cell organelles. The reason that this is so, is because there would be more room them to carry oxygen. Anyways, this means that red blood cells lack a mitochondrion, so they cannot possibly synthesise ATP in bulk, because we know that the mitochondria is the organelle where most of the ATP is producer (32-34 ATP molecules per glucose). However, there are two forms of cellular respiration, aerobic and anaerobic. Aerobic respiration involves the use of oxygen in the ETC, which occurs in the cristae of the mitochondrion, but remember, there are none in RBCs. So, red blood cells must synthesise ATP in another form, hence they undertake the anaerobic pathway. This means that glucose diffuses into the cytoplasm of RBCs and is broken down in the cytoplasm and then undergoes the further biochemical reactions of anaerobic respiration.

Oh and let me test your knowledge here. Can RBCs synthesise proteins? Why/Why not? Whatever your answer is, then how would RBCs intake haemoglobin? (the protein that carries oxygen and is found in abundance in RBCs).

Thank you for the kind words, it means a lot

[Splash-Tackle-Flail]

Okay so I may go into too much detail here, so beware. Red blood cells (of humans) are enucleated, that is, they do not have a nucleus. These cells lose their nucleus and so they do not have the genetic code (DNA) to synthesise the proteins that are required for the production of the cell organelles. The reason that this is so, is because there would be more room them to carry oxygen. Anyways, this means that red blood cells lack a mitochondrion, so they cannot possibly synthesise ATP in bulk, because we know that the mitochondria is the organelle where most of the ATP is producer (32-34 ATP molecules per glucose). However, there are two forms of cellular respiration, aerobic and anaerobic. Aerobic respiration involves the use of oxygen in the ETC, which occurs in the cristae of the mitochondrion, but remember, there are none in RBCs. So, red blood cells must synthesise ATP in another form, hence they undertake the anaerobic pathway. This means that glucose diffuses into the cytoplasm of RBCs and is broken down in the cytoplasm and then undergoes the further biochemical reactions of anaerobic respiration.

Oh and let me test your knowledge here. Can RBCs synthesise proteins? Why/Why not? Whatever your answer is, then how would RBCs intake haemoglobin? (the protein that carries oxygen and is found in abundance in RBCs).

Just a preface: <3 <3 <3

Answers to your Qs: No, RBC's can't synthesise proteins as they have no DNA (required to make mRNA and proteins). I'm frankly not too sure about how RBCs intake haemoglobin, but I'm assuming it diffuses into the RBCs when they're being produced in the bone marrow (clutching at straws here!)

Anyways, I got more questions- so for context we're learning about tonicity, and comparing the infusion of iso-osmolar urea with iso-osmolar dextrose solutions. So I know urea is permeable so infusing iso-osmolar urea would result in the urea diffusing into the red blood cells in the body, making the red blood cells osmole concentration greater than the blood's so water then diffuses into the RBCs and lyses it. But apparently for the dextrose solution, dextrose is initially impermeable, and thus can be infused into the body. But with protein channels wouldn't dextrose be permeable and thus result in the same cruel fate as urea?

[cosine]

Just a preface: <3 <3 <3

Answers to your Qs: No, RBC's can't synthesise proteins as they have no DNA (required to make mRNA and proteins). I'm frankly not too sure about how RBCs intake haemoglobin, but I'm assuming it diffuses into the RBCs when they're being produced in the bone marrow (clutching at straws here!)

Anyways, I got more questions- so for context we're learning about tonicity, and comparing the infusion of iso-osmolar urea with iso-osmolar dextrose solutions. So I know urea is permeable so infusing iso-osmolar urea would result in the urea diffusing into the red blood cells in the body, making the red blood cells osmole concentration greater than the blood's so water then diffuses into the RBCs and lyses it. But apparently for the dextrose solution, dextrose is initially impermeable, and thus can be infused into the body. But with protein channels wouldn't dextrose be permeable and thus result in the same cruel fate as urea?

I don't have much background with dextrose solution, or the molecular size of it. All I can say is that certain molecules that for a molecule to be able to diffuse through protein channels, they must:
- Be relatively small, but relatively larger than water molecules, oxygen etc..
- Be polar substances, as inside the protein channels, there is a polar lining, and hence only polar molecules can pass through them.
- Be at a higher concentration outside the cell than inside, and only then they can diffuse through into the cell to reach equilibrium.

I will take a guess here. Apparently dextrose is a form of glucose that is derived from starches, basically when starch breaks down into its respective monomers, they are called dextrose. What do you mean when you say it is initially impermeable, and thus can be infused into the body? Do you mean that dextrose is forcibly taken up into cells? Just give me more background info and I would love to help, but this is such a specific question haha

[pi]

5% glucose/dextrose infusion increases both intracellular and extracellular fluid volume, so yeah if you infuse enough for long enough (which never practically happens) you can follow the ill fate of infusing urea and lyse the RBCs.

Guessing this comes from Prof CW's lecture? If so, absolute mindfuck hahahaha

[Splash-Tackle-Flail]

I don't have much background with dextrose solution, or the molecular size of it. All I can say is that certain molecules that for a molecule to be able to diffuse through protein channels, they must:
- Be relatively small, but relatively larger than water molecules, oxygen etc..
- Be polar substances, as inside the protein channels, there is a polar lining, and hence only polar molecules can pass through them.
- Be at a higher concentration outside the cell than inside, and only then they can diffuse through into the cell to reach equilibrium.

I will take a guess here. Apparently dextrose is a form of glucose that is derived from starches, basically when starch breaks down into its respective monomers, they are called dextrose. What do you mean when you say it is initially impermeable, and thus can be infused into the body? Do you mean that dextrose is forcibly taken up into cells? Just give me more background info and I would love to help, but this is such a specific question haha

My current theory is that we are only dealing with the infusion site, so since dextrose can only permeate via protein channels in the RBCs, they would permeate at a much slower rate than something that would quickly prompt cell lysis such as urea (which can permeate via the phospholipid bilayer membrane). So it's more gradual change and given the dextrose is metabolised and all, the
"tonicities" of the Extracellular fluid and intracellular fluid aren't lethally great. I think Prof CW is going through it more tomorrow so I can tell you about it.

And thanks so much I genuinely appreciate it (btw how does haemoglobin get in RBCs if RBCs can't produce it- i.e. was my answer on the right track?)

5% glucose/dextrose infusion increases both intracellular and extracellular fluid volume, so yeah if you infuse enough for long enough (which never practically happens) you can follow the ill fate of infusing urea and lyse the RBCs.

Guessing this comes from Prof CW's lecture? If so, absolute mindfuck hahahaha

Gee just about everything has an ill fate in bio..

Yeah, I think I'm starting to fit the criteria for Wilfred Owen's "Mental Cases" poem... "— These are men whose minds the Dead osmolarity have ravished. Memory fingers in their hair of murders...because like a lone red blood cell in an infinite bath of terror, we are the forsaken..." -Wilfred Owen's 1914 remark after sitting through his very first lecture of med school.

[vox nihili]

Just going to jump in here and say a couple of things:



-glucose is not taken up by channels, it is taken up by carrier proteins. As a general rule, channels are usually reserved for ions, whereas carriers can do both ions and polar molecules. This is obviously not a hard-and-fast rule, but as a rule-of-thumb it's right nine times out of ten.
-red blood cells don't take up haemoglobin. Rather, they start off as cells that can produce proteins and, as they develop, kick out their nucleus. So it's not a matter of getting haemoglobin in that makes an anuclear RBC, but rather, a matter of getting the nucleus out

[johnhalo]

Is oxygen required for the Krebs Cycle or Electron Transport Chain? I always believed it was needed in the ETC, and not Krebs, but I've read that it is needed for the Krebs Cycle. Clarification on this would be wonderful.

In other words, is oxygen an input of Krebs or ETC.

Thanks

[vox nihili]

Is oxygen required for the Krebs Cycle or Electron Transport Chain? I always believed it was needed in the ETC, and not Krebs, but I've read that it is needed for the Krebs Cycle. Clarification on this would be wonderful.

In other words, is oxygen an input of Krebs or ETC.

Thanks

ETC

[qwertyqwerty]

Are coenzymes used up in an enzyme reaction? What about cofactors?