VCE Biology Question Thread

[blacksanta62]

Currently do cell signalling hormones and wondering if anyone can give me an example of a hormone for each of the following:
-Endocrine signalling hormones: Would testosterone, estrogen and other growth hormones be suitable examples?
-Panacrine signalling hormones: I have no examples for this
-Autocrine signalling: I have no examples for this

Thank you

[vox nihili]

How exactly does Calcium act as a second messenger molecule in the presynaptic neuron? Specifically, how does it allow the release of neurotransmitters from the synaptic terminal into the synapse? My teacher mentioned something about calmodulin, but never really explained properly. I know the specifics aren't required for the VCE syllabus, but I feel as though it would be a major help in understanding neuronal function in relation to signal transduction...
Thanks!

I don't know the exact details of the proteins involved, but basically it activates cellular machinery that helps to drag the vesicles to the membrane and then helps to pull it in and fuse it. Without that, vesicles won't fuse with the membrane.

Currently do cell signalling hormones and wondering if anyone can give me an example of a hormone for each of the following:
-Endocrine signalling hormones: Would testosterone, estrogen and other growth hormones be suitable examples?
-Panacrine signalling hormones: I have no examples for this
-Autocrine signalling: I have no examples for this

Thank you

Theoretically, any endocrine signalling molecules can be paracrine or autocrine. Just remember not to call paracrines and autocrines hormones. Hormone is a termed reserved only for endocrine.

Some common paracrines include things like histamine, bradykinin, NO, TGF-beta, cytokines, chemokines

[vox nihili]

Is the link reaction from pyruvate to acetyl-coA apart of the Krebs cycle? If a question asked how many CO2 molecules were produced in the Krebs cycle per glucose molecule, would I answer as 6 (this assumes the link reaction is apart of the Krebs cycle) or 4 (this assumes the link reaction is not apart of the Krebs cycle).

I think six would be ok. They'd take both. It's not really a part of the Kreb's cycle, but in VCE land it kind of is

[blacksanta62]

Theoretically, any endocrine signalling molecules can be paracrine or autocrine. Just remember not to call paracrines and autocrines hormones. Hormone is a termed reserved only for endocrine.

Some common paracrines include things like histamine, bradykinin, NO, TGF-beta, cytokines, chemokines

Thanks T-Rav, would I just call them paracrines and autocrines or is there something at the end/beginning. Thank you

[ShereeL]

Hmmm they don't always, not sure it's part of the VCE course. But it's basically because lipid-soluble hormones are typically responsible for transcriptional responses, whereas protein hormones, generally, complete their actions by modulating enzymes etc.

Glycogen. Glucose is not a storage molecule.

Wait, so does this mean the Glycogen in yeast has to be converted into Glucose before it undergoes anaerobic respiration? and does that count as a step in the alcoholic fermentation from yeast?

[vox nihili]

Thanks T-Rav, would I just call them paracrines and autocrines or is there something at the end/beginning. Thank you

Paracrines and autocrines are fine

Wait, so does this mean the Glycogen in yeast has to be converted into Glucose before it undergoes anaerobic respiration? and does that count as a step in the alcoholic fermentation from yeast?

No, glucose can go straight into the pathway.

[haydencooper]

Can someone help with these questions please?

1. Explain how a single odorant molecule given off by food could be detected by a cell and therefore elicit a well co-oridnated response such as the planarian moving to the food (and provide name of process)

2. What is the general function of a hormone?

3. The amount of hormone Z present in the circulatory system of the planaria are shown to vary. What could act upon cell Z to stop hormone production?

4. Explain the cellular mechanisms of how apoptosis works

Any help would be greatly appreciated!!

[blacksanta62]

Hello, just a few questions that have me stumped.
1) How does a very small amount of hormone exert such a large reaction with a cell?
2) Why do lipid based hormones have to be carried by proteins in the blood while protein based hormones can travel through the blood freely?

Thank you

[Photon]

What's up guys.

A few questions from your main man:

- Can carbon dioxide be used if in the L-I stage of if we were to stop light from entering the cell and had no LD stage

- How do the hydrogen ions in both photosynthesis and respiration have an effect on the pH of the cell?

- When is ATPase ever used to break down ATP?

Thanks!

[mtDNA]

Hello, just a few questions that have me stumped.
1) How does a very small amount of hormone exert such a large reaction with a cell?
2) Why do lipid based hormones have to be carried by proteins in the blood while protein based hormones can travel through the blood freely?

Thank you

1) A small concentration of hormone has the potential to exert such a large reaction in the target cell due to the process of signal amplification. For instance, when a signalling molecule binds to a G protein coupled receptor (GPCR), a G protein becomes activated and acts as a relay molecule, which then activates adenylyl cyclase, a protein found embedded in the plasma membrane. As a result, the protein changes conformation and thus gains an active site. Therefore, ATP is then enabled to bind to this site and is converted into cyclic adenosine monophosphate (cAMP). These cAMP molecules (secondary messenger molecules) produced may go on to further activate even more molecules (known as protein kinases), which then activate even more molecules which finally bring about a cellular response. In this process, one signalling molecule acts as the ligand and binds to the target cell's receptor. 100 cAMP molecules may be activated - these then can activate a further two protein kinases each, hence activating a total of 200 protein kinases. Then... these go on to activate EVEN MORE molecules! As you can see, we went from 1 signalling molecule to >200 other activated molecules, hence demonstrating how a small amount of hormone can exert such a large reaction in the target cell

2) As you would know from your studies of biomacromolecules in AoS1 Bio, steroids are hydrophobic (or lipophilic) and thus repel water. As a result, they are unable to pass through the circulatory system as the majority of the plasma component of blood is water. Therefore, they require a 'carrier protein' (which is hydrophilic), however, I'm uncertain to how exactly the carrier protein works - I'd assume it acts as a 'capsule' surrounding the steroid hormone to prevent interaction of water, but I'm not too sure... On the contrary, Peptide and amino acid derivatives are hydrophilic (or lipophobic). As a result, they are able to interact which water and thus can flow freely in the plasma of blood.

I hope this helps

[mtDNA]

Can someone help with these questions please?

1. Explain how a single odorant molecule given off by food could be detected by a cell and therefore elicit a well co-oridnated response such as the planarian moving to the food (and provide name of process)

2. What is the general function of a hormone?

3. The amount of hormone Z present in the circulatory system of the planaria are shown to vary. What could act upon cell Z to stop hormone production?

4. Explain the cellular mechanisms of how apoptosis works

Any help would be greatly appreciated!!

1) I'm not too sure about this question, so i'll leave it for someone else to answer. I''t attempt it anyway - I believe it relates to the fact that the odourant molecule is complementary to a specific receptor found embedded in the plasma membrane of the planarian cell. Therefore. it acts as a signalling molecule in which it binds to a receptor on the planarian cell, hence causing  a signal transduction pathway, which in turn leads to a cellular response. This will then allow for the movement of the planarian towards to the food source (I'm not certain if this answer is correct...)

2) The general function of a hormone is to act as a distant signalling molecule which acts on a target cell located away from the endocrine glad that produced and secreted it. This signalling molecule then causes a cellular response from the target cell/s. As a result, it allows for the coordination of the organism as it regulates homeostasis in the organism - the homeostatic cellular response may either reinforce (positive feedback) or counteract (negative feedback) the initial stimulus

3) (this may be incorrect...) A hormone from another cell, or the same cell, may be produced to act on cell Z. I'd assume that the hormone would act as an inhibitory signal which would temporarily prevent the transcription of the specific gene that translates and produces hormone Z. (May someone notify me if this is correct, and if not, what the actual response should be...)

4) In apoptosis, there are two pathways - the intrinsic pathway and the extrinsic pathway. In essence, the intrinsic pathway is when apoptosis is signalled from within the cell, while the extrinsic pathway is when apoptosis is signalled from another cell/external source. Despite the two pathways, the effects caused are quite similar: proteins called 'caspases' become activated and cleave proteins within the cell, including the cytoskeleton and nuclear lamins (nuclear envelope). Respectively, this causes blebbing (or Zeiosis) and the degradation of the nuclear envelope. Simultaneously, the chromatin is fragmented. After these processes occur, a phagocytic cell engulfs the degrading cell and releases cytokines (which act to inhibit an inflammatory response).

In saying this, I also have a question on apoptosis: In the Intrinsic pathway, how exactly is cytochrome C activated in the mitochondria to initiate the caspase cascade? - Thanks

[vox nihili]

1) I'm not too sure about this question, so i'll leave it for someone else to answer. I''t attempt it anyway - I believe it relates to the fact that the odourant molecule is complementary to a specific receptor found embedded in the plasma membrane of the planarian cell. Therefore. it acts as a signalling molecule in which it binds to a receptor on the planarian cell, hence causing  a signal transduction pathway, which in turn leads to a cellular response. This will then allow for the movement of the planarian towards to the food source (I'm not certain if this answer is correct...)

2) The general function of a hormone is to act as a distant signalling molecule which acts on a target cell located away from the endocrine glad that produced and secreted it. This signalling molecule then causes a cellular response from the target cell/s. As a result, it allows for the coordination of the organism as it regulates homeostasis in the organism - the homeostatic cellular response may either reinforce (positive feedback) or counteract (negative feedback) the initial stimulus

3) (this may be incorrect...) A hormone from another cell, or the same cell, may be produced to act on cell Z. I'd assume that the hormone would act as an inhibitory signal which would temporarily prevent the transcription of the specific gene that translates and produces hormone Z. (May someone notify me if this is correct, and if not, what the actual response should be...)

4) In apoptosis, there are two pathways - the intrinsic pathway and the extrinsic pathway. In essence, the intrinsic pathway is when apoptosis is signalled from within the cell, while the extrinsic pathway is when apoptosis is signalled from another cell/external source. Despite the two pathways, the effects caused are quite similar: proteins called 'caspases' become activated and cleave proteins within the cell, including the cytoskeleton and nuclear lamins (nuclear envelope). Respectively, this causes blebbing (or Zeiosis) and the degradation of the nuclear envelope. Simultaneously, the chromatin is fragmented. After these processes occur, a phagocytic cell engulfs the degrading cell and releases cytokines (which act to inhibit an inflammatory response).

In saying this, I also have a question on apoptosis: In the Intrinsic pathway, how exactly is cytochrome C activated in the mitochondria to initiate the caspase cascade? - Thanks

Well beyond VCE knowledge, so you don't need to know

Very basically, the intrinsic pathway is set into action when proteins blast holes in the mitochondria (proteins are Bax and Bak). Cytochrome C is held in the mitochondria, so when it becomes leaky, cytochrome C pops out. It then binds to Caspase 9 and another protein called Apaf-1, forming a complex called the Apoptosome, which then goes on to activate other caspases and then apoptosis happens...

[Shax]

Guys, how can a plant absorb materials that are on their leaves if it has an outer cuticle layer that acts as an impermeable boundary for the leaf tissue? If we spray a solution of a plant hormone onto a plant, how do leaves absorb this substance? The stomatal pores take in gases; what structure absorbs liquids other than the root hairs?
  

[haydencooper]

1) I'm not too sure about this question, so i'll leave it for someone else to answer. I''t attempt it anyway - I believe it relates to the fact that the odourant molecule is complementary to a specific receptor found embedded in the plasma membrane of the planarian cell. Therefore. it acts as a signalling molecule in which it binds to a receptor on the planarian cell, hence causing  a signal transduction pathway, which in turn leads to a cellular response. This will then allow for the movement of the planarian towards to the food source (I'm not certain if this answer is correct...)

2) The general function of a hormone is to act as a distant signalling molecule which acts on a target cell located away from the endocrine glad that produced and secreted it. This signalling molecule then causes a cellular response from the target cell/s. As a result, it allows for the coordination of the organism as it regulates homeostasis in the organism - the homeostatic cellular response may either reinforce (positive feedback) or counteract (negative feedback) the initial stimulus

3) (this may be incorrect...) A hormone from another cell, or the same cell, may be produced to act on cell Z. I'd assume that the hormone would act as an inhibitory signal which would temporarily prevent the transcription of the specific gene that translates and produces hormone Z. (May someone notify me if this is correct, and if not, what the actual response should be...)

4) In apoptosis, there are two pathways - the intrinsic pathway and the extrinsic pathway. In essence, the intrinsic pathway is when apoptosis is signalled from within the cell, while the extrinsic pathway is when apoptosis is signalled from another cell/external source. Despite the two pathways, the effects caused are quite similar: proteins called 'caspases' become activated and cleave proteins within the cell, including the cytoskeleton and nuclear lamins (nuclear envelope). Respectively, this causes blebbing (or Zeiosis) and the degradation of the nuclear envelope. Simultaneously, the chromatin is fragmented. After these processes occur, a phagocytic cell engulfs the degrading cell and releases cytokines (which act to inhibit an inflammatory response).

In saying this, I also have a question on apoptosis: In the Intrinsic pathway, how exactly is cytochrome C activated in the mitochondria to initiate the caspase cascade? - Thanks

Thanks heaps!!

[haydencooper]

Can someone help answer this question please?

What is negative feedback and how can it result in the planarian being stationary?

(Just some background info, the planarians are responsive to light and move away from a light source into darkness). I had my own idea of an answer for this but wanted to see if someone else could help with one first