Just wondering if someone can answer a few queries I have
1. Why do some cells produce 36 ATP via aerobic respiration while others produce 38? (Some sources say that the extra 2 ATP comes from glycolysis while others say that it comes from the electron transport chain)
2. Why is it that if oxygen is not present, the Krebs cycle (as well as the electron transport chain) comes to a stop?
3. Can I say that hormones are released into extracellular fluid instead of the bloodstream? (Is there a difference?)
4. Does signal transduction happen with lipid-based hormones? I'm pretty sure it does but could someone just briefly explain the "cascade of events" that occurs?
5. Regarding apoptosis: where does the extrinsic signal come from?
Thank-you in advance!
1. In some cells the ETC is more efficient than others, hence the difference. I highly doubt that it's because of different ways of doing glycolysis.
2. Because NADH/FADH
2 aren't being used by the ETC, this feeds back and halts their production by the Kreb's cycle. Not necessary to know this in VCE though, of course and it is a little more complicated than I've explained, but this should do.
3. Absolutely not. Extracellular fluid is the fluid in which all tissues are bathed, whereas blood is fluid contained within the lumina (sing. lumen, just means a hollow tube) of blood vessels. Hormones are exclusively released into blood vessels and not extracellular fluid (technically hormones can be released into both, but they're not acting as a hormone if they're in the tissue, they're acting as a paracrine in that context—basically, paracrines and hormones can be the same molecule, just in different places).
4. It does. Lipid hormone comes in, binds its receptor and the receptor moves to the nucleus where it helps to transcribe genes. Post-VCE a lot more information is added to this, but you'll just have to accept that this is signal transduction even if it doesn't have the stages you're used to.
5. Any number of places. Viruses. Damaged cells. Immune cells. It's just a signalling molecule, much like a hormone actually.