VCE Biology Question Thread

[katiesaliba]

You are correct! Sodium potassium pumps still work during refractory periods.

Would they always be working then, even during the absolute refractory period?

[alchemy]

Would they always be working then, even during the absolute refractory period?

Refer to this image: http://imgur.com/b3QPXAq
The 'absolute refractory period' refers to the depolarisation and depolarisation stages.
The 'relative refractory period' refers to the hyper-polarisation stage itself.
The sodium and potassium pumps work during both these periods.

[slothpomba]

To clarify, sodium-potassium pumps work to maintain the resting phase in neurons, right? So the pumps would also work during the relative refractory period after hyperpolarisation? 

These do not become refractory, they are always "switched on". Think of them as part of a critical infrastructure of the cell - the hospital, power plant or water supply. We can't really shut off any of these in modern society because they're so crucial and it'd be nuts to have opening and closing hours for hospitals or power. The Na+/K+ ATPase pumps are similar. It is important that the resting membrane potential be maintained, these pumps as important to be constantly operating to the neuron as hospitals are important to be constantly operating to us.

Sodium pumps OR Potassium pumps can be made refractory but for as far as you need to know, Na+/K+ ATPase pumps are always on. They also play a (small) role in returning the membrane to its resting potential after the peak of the AP.

[robert.pernes]

HI all, I have a few questions regarding Signal transduction of proteins and lipids into the cell membrane.

Firstly, how does a protein enter the cell via signal transduction and what happens after

And Secondly, How does a lipid enter a cell via signal transduction and what happens after

[howlingwisdom]

HI all, I have a few questions regarding Signal transduction of proteins and lipids into the cell membrane.

Firstly, how does a protein enter the cell via signal transduction and what happens after

And Secondly, How does a lipid enter a cell via signal transduction and what happens after

Proteins and lipids do NOT enter a cell but instead initiate signal transduction (a cascade of events that happen inside of the cell after they bind to their specific receptors, leading to a cellular response).
Proteins, which are water-soluble/hydrophillic in nature (hence unable to pass through the phospholipid bilayer) bind to a specific receptor on the surface of the cell membrane. This causes a cascade of events inside the cell (like the activation of G-proteins which activates second messengers like cAMP which amplify the signal from the membrane receptors to target molecules inside the cell) which lead to an amplified cellular response.
Lipids, which are hydrophilic, are able to pass through the phosphilipid bilayer and bind to a specific intracellular receptor (in the cytoplasm or nucleus). For instance, lipid-based hormones bind to a receptor forming a hormone-receptor complex which enters the nucleus and modfies gene expression in the cell. Lipid-based hormones generally affects gene expression/modifies genes.

Hope this clears a few things up and helpsl! (Someone correct me if I've missed anything/am incorrect haha)

[Rishi97]

Explain the role of auxin (IAA) in the following plant growth processes:
a) Apical dominance
b) Stem growth
c) Secondary growth

Thanks

Could someone please help me
Much appreciated

[swagsxcboi]

Proteins and lipids do NOT enter a cell but instead initiate signal transduction (a cascade of events that happen inside of the cell after they bind to their specific receptors, leading to a cellular response).
Proteins, which are water-soluble/hydrophillic in nature (hence unable to pass through the phospholipid bilayer) bind to a specific receptor on the surface of the cell membrane. This causes a cascade of events inside the cell (like the activation of G-proteins which activates second messengers like cAMP which amplify the signal from the membrane receptors to target molecules inside the cell) which lead to an amplified cellular response.
Lipids, which are hydrophilic, are able to pass through the phosphilipid bilayer and bind to a specific intracellular receptor (in the cytoplasm or nucleus). For instance, lipid-based hormones bind to a receptor forming a hormone-receptor complex which enters the nucleus and modfies gene expression in the cell. Lipid-based hormones generally affects gene expression/modifies genes.

Hope this clears a few things up and helpsl! (Someone correct me if I've missed anything/am incorrect haha)

generally a very good answer but lipids are hydrophobic, and they enter the cell, passing through the phospholipid bilayer.

[howlingwisdom]

generally a very good answer but lipids are hydrophobic, and they enter the cell, passing through the phospholipid bilayer.

Oops my bad - thank you for pointing that out!

[howlingwisdom]

Why can't an action potential be initiated during the refractory period?

[robert.pernes]

Proteins and lipids do NOT enter a cell but instead initiate signal transduction (a cascade of events that happen inside of the cell after they bind to their specific receptors, leading to a cellular response).
Proteins, which are water-soluble/hydrophillic in nature (hence unable to pass through the phospholipid bilayer) bind to a specific receptor on the surface of the cell membrane. This causes a cascade of events inside the cell (like the activation of G-proteins which activates second messengers like cAMP which amplify the signal from the membrane receptors to target molecules inside the cell) which lead to an amplified cellular response.
Lipids, which are hydrophilic, are able to pass through the phosphilipid bilayer and bind to a specific intracellular receptor (in the cytoplasm or nucleus). For instance, lipid-based hormones bind to a receptor forming a hormone-receptor complex which enters the nucleus and modfies gene expression in the cell. Lipid-based hormones generally affects gene expression/modifies genes.

Hope this clears a few things up and helpsl! (Someone correct me if I've missed anything/am incorrect haha)

WOW THANK YOU SO MUCH!

[katie101]

Explain whether all hormones need to enter the bloodstream to be able to affect a cell.

Thanks

[MM1]

Explain whether all hormones need to enter the bloodstream to be able to affect a cell.

Thanks

Not all hormones need to enter the blood stream to affect a cell. Sometimes a hormone may act on the cell that secretes it (autocrine signalling) or to nearby adjacent cells (paracrine).

[katie101]

Not all hormones need to enter the blood stream to affect a cell. Sometimes a hormone may act on the cell that secretes it (autocrine signalling) or to nearby adjacent cells (paracrine).

Thanks!!

[howlingwisdom]

What are the possible consequences/results of a toxin or botox in a neuromuscular junction?

[MM1]

What are the possible consequences/results of a toxin or botox in a neuromuscular junction?

Prevents the contraction of muscles?