VCE Biology Question Thread

[TheAspiringDoc]

When a  solute dissolves in a solvent :
-solute particles separate
-solvent particles separate
-solvent and solute bond (only dissolve if the bonds between solute and solvent is stronger than it is between solvent and solute alone) 
^this is like unit 2 chem version of explaining dissolving.
But in regards to biology u just need to know that  'like dissolves like' meaning that polar will only dissolve in polar and non polar in non polar. This is why fats are insoluble in water. Fats are non polar and water is polar. Strong bonds do not form between the two. Polar , however , can dissolve in water because water is polar itself.  Amphipathic in VCE bio is usually used to describe the phospholipid molecule. Amphipathic refers to the fact that a portion of it is hydrophilic/polar (in regards to the phospholipid the phosphate heads)  and the other portion is hydrophobic/non polar (fatty acid tails) .

Not sure bout your last q.
Hope this helps 

Thanks Sunshine!

[cosine]

Can some please explain to me, does the term 'amphipathic' refer to proteins, or is it something that concerns polar molecules such as water, or all of them? I've found several different definitions and am a little stumped.

Also, why is it that triglicerydes are used for energy storage and all the rest of it? Like I know it is what's used, but why is it in particular used? Like why not a diglyceride or quadglyceride or something like that?

Thanks

Amphipathic means that a certain molecule, or anything in fact, has two parts to it. It probably can refer to proteins, if the protein has two opposing parts. But as sunshine98 said, in VCE Biology, it usually refers to the nature of the phospholipids, as they have two natures, a hydrophilic phosphate head, and a hydrophobic fatty acid region.

First of all, quadglycerides do not exist, but diglycerides do. So you have diglyceride and triglyceride, diglycerides have two fatty acid hydrocarbon chains, and triglycerides have three. Which one would be more efficient for energy storage and source? (Remember, energy comes from breaking down bonds, and clearly the triglycerides would have more bonds!)

Hopefully this helps, but honestly in VCE Biology, just know that triglycerides are an excellent source of energy, nothing more or less!

[TheAspiringDoc]

Amphipathic means that a certain molecule, or anything in fact, has two parts to it. It probably can refer to proteins, if the protein has two opposing parts. But as sunshine98 said, in VCE Biology, it usually refers to the nature of the phospholipids, as they have two natures, a hydrophilic phosphate head, and a hydrophobic fatty acid region.

First of all, quadglycerides do not exist, but diglycerides do. So you have diglyceride and triglyceride, diglycerides have two fatty acid hydrocarbon chains, and triglycerides have three. Which one would be more efficient for energy storage and source? (Remember, energy comes from breaking down bonds, and clearly the triglycerides would have more bonds!)

Hopefully this helps, but honestly in VCE Biology, just know that triglycerides are an excellent source of energy, nothing more or less!

Okay, that really helps - thanks!

But for the sake of intuition, why is it that quad and pent etc. glycerides don't exist if the extra hydrolysis allows for extra release of energy? Perhaps it might be something to do with if you have more fatty acid tails you reduce the surface that can undergo hydrolysis, making it a slower means of energy release?

And how come disturbances such as heat or unsuitable pH are thought to denature the secondary and tertiary structures of a protein but not its quarternary structure?

[Jay.C]

Hey new biologists, I see some of you are beginning to ask questions!! Just a word of advice as I see many of the questions being asked are quite advanced and some far beyond a vce biology level. It's great to want to learn more and be interested, bio is extremely interesting but remember to not make it harder then it has to be!! The study design is there for a reason, you'll only be asked questions on the topics listed, so please don't stress yourselves out with learning greater amounts of content then you need to!! However if you want to dig deeper and it's not putting any of your other subjects to detriment go for it!! 

[cosine]

Okay, that really helps - thanks!

But for the sake of intuition, why is it that quad and pent etc. glycerides don't exist if the extra hydrolysis allows for extra release of energy? Perhaps it might be something to do with if you have more fatty acid tails you reduce the surface that can undergo hydrolysis, making it a slower means of energy release?

And how come disturbances such as heat or unsuitable pH are thought to denature the secondary and tertiary structures of a protein but not its quarternary structure?

I took this from TSFX, and I still remember it. The reason why they dont exist is because the glycerol backbone, which binds to the fatty acid hydrocarbon chains, only has three available spots, so the maximum number of chains that can bind is 3. Also, what made me believe it is the case with phospholipids. I also asked myself the same question, but then realised that if the glycerol backbone has three spots, then that explains also why phospholipids has one phosphate group and only two fatty acid chains, because only three molecules can bind to the glycerol backbone! At this moment, it all kicked in for me!

For your second question, well, it does. Think about the quaternary structure of a protein, lets look at haemoglobin which is composed of four polypeptide chains (4 tertiary structured proteins). Now, say I increased the temperature a lot and it exceeds the protein's optimal temp, the bonds in the protein start to break and the shape of the protein starts to denature. But how does a quaternary structure hold? Well, there are bonds within each polypeptide chain that adhere together and bring together the complete quaternary level, and if these bonds that link the chains (four in our case) together breaks, then the quaternary structure is denatured. This may be too deep for Biology in VCE, and to be honest you probably won't get asked about which level denatures etc.. You are only required to know the process of denaturation, the effects leading to it, and why it happens, which im pretty sure you already know... xD

Hope this helped!

[sunshine98]

Okay, that really helps - thanks!

But for the sake of intuition, why is it that quad and pent etc. glycerides don't exist if the extra hydrolysis allows for extra release of energy? Perhaps it might be something to do with if you have more fatty acid tails you reduce the surface that can undergo hydrolysis, making it a slower means of energy release?

And how come disturbances such as heat or unsuitable pH are thought to denature the secondary and tertiary structures of a protein but not its quarternary structure?

First q -glycerol can undergo condensation with only up to 3 fatty acid chains cause it only has three hydroxy groups (this is chem stuff tho)
Second q- I was always taught that denaturation of quaternary can happen by the factors that u have  mentioned

[TheAspiringDoc]

Cheers buddies

What happens when DNA is denatured - is its loss of function irreversible? or does it accumulate mutations and continue to do things, albeit in a cancerous manner?

[sunshine98]

Cheers buddies

What happens when DNA is denatured - is its loss of function irreversible? or does it accumulate mutations and continue to do things, albeit in a cancerous manner?

Denaturation of DNA occurs when the hydrogen bonds between the two strands are broken by high temps.I guess  it can be considered reversible cause once temp is decreased again the two strands will anneal ( this forms the foundation for a technique known as DNA Hybridisation - u will learn in unit 4 )
Mutations are a whole other thing, quite distinct from DNA denaturation ( as far as I know from VCE bio)
Hope this helps 

[Jay.C]

Cheers buddies

What happens when DNA is denatured - is its loss of function irreversible? or does it accumulate mutations and continue to do things, albeit in a cancerous manner?

When DNA denatures the hydrogen bonds between the complementary nucleotides break, causing two single nucleotide strands to result. This process is reversible and is infact essential for some processes e.g. Polymerase chain reaction. As for it accumulating mutations or behaving in a cancerous way, I'm not to sure of the effects denaturing would have.     

edit: sunshine98 beat me to it.

[Arithmetic]

Hello everyone! 

I would just like to ask if anybody could explain the modes of transport of soluble substances across the plasma membrane. And explain each of the following: Simple diffusion, facilitated diffusion, osmosis and active transport.

Thanks.

[cosine]

Hello everyone! 

I would just like to ask if anybody could explain the modes of transport of soluble substances across the plasma membrane. And explain each of the following: Simple diffusion, facilitated diffusion, osmosis and active transport.

Thanks.

Well in Biology, when the word 'soluble' is used, it typically describes a molecule (group of atoms) that are able to dissolve in water. So when we talk about soluble substances transporting across plasma membranes, then were talking about molecules, that are able to diffuse in water, that can simply diffuse through the membranes.

Simple diffusion:
This is the process where either small, non-polar substances can simply diffuse through the cell membrane of cells, because the chemical nature of the membrane is lipophilic, and so the non-polar (lipophilic) substances can diffuse through, as they are attracted to the fatty acid chains. Also, some polar, relatively small molecules such as water and carbon dioxide can still diffuse simply through the plasma membrane, despite being polar, and despite being repelled from the fatty acid chains of phospholipids, because they're so small and can just go through the small pores of the membranes. Remember, simple diffusion is diffusion, the movement of particles from a relatively HIGH concentration to a region of LOW concentration, ALONG the concentration gradient. Diffusion is passive; it does not require energy to proceed (ATP).

Facilitated diffusion:
Facilitated diffusion is the process where particles/molecules are transported from a region of relatively HIGH concentration to a region of LOW concentration, ALONG the gradient, through a plasma membrane with the FACILITATION (aid) of a protein channel/carrier. So, this means that when a molecule is too large, and possibly also polar, and hence cannot freely/simply diffuse the plasma membrane, then it must use some other scheme of transport, right? In this case, these relatively large, polar molecules, such as glucose, will need to be transported into/out of cells through proteins molecules that are pre-embedded into the membrane. This process is also passive; it does not require energy (ATP).

Osmosis:
Osmosis is literally the diffusion of water molecules, through a plasma membrane in/out of cells. Osmosis occurs when water molecules exist at a higher concentration, and diffuse inside a cell, where their concentration is relatively low. Diffusion occurs until equilibrium is achieved, that is, when the amount of water is equal both inside and outside the cells. Osmosis is passive; it does not require energy (ATP).

Active transport:
This is the transport of molecules from a region of relatively LOW concentration to a region of HIGH concentration, AGAINST the concentration gradient, through a plasma membrane. Active transport occurs when molecules from from low to high, and this process occurs actively, that is, it require energy to occur (ATP).

I hope this helped xD

[sunshine98]

Hello everyone! 

I would just like to ask if anybody could explain the modes of transport of soluble substances across the plasma membrane. And explain each of the following: Simple diffusion, facilitated diffusion, osmosis and active transport.

Thanks.

The way substances are transported across a membrane is determined by 2 things - polarity and size.
If something is small it will move much more easily through the membrane than  if it is large.
If something is polar it will not move through as easily as something that is non polar.
Diffusion or the movement of a substance is affected by - temperature  and steepness of the concentration gradient.
Concentration gradient refers to the difference between the concentrations on either side of the membrane. If one side has an extremely higher concentration than the other than the concentration gradient is steep and diffusion will occur. Diffusion is passive (means no energy) the movement of particles from an area of high concentration to an area of low concentration so a some sort of balance can be achieved. This just entails the particles simply passing through the membrane and no energy is required.
However, the diffusion of water (if we can call it that) is referred to as osmosis. Osmosis is the movement of water particles from an area of high free water particles to an area of low free water particles. So if you have a solution separated by a semi permeable memberane (one that only allows the movement of some particles and not other) water will move from the side that has more free water particles (that is , water particles not bonded to the solute) to the area where there is less (that is , the area where most water particles are bonded to solute particles) .
But remember the conditions (polarity and size) that I said earlier. If a particle is large or polar , due to the nature of the phospholipid bilayer it cannot simply diffuse across the membrane so it undergoes a process known as facilitated diffusion. This entails the use of a membrane protein that aids in transporting the substance across the membrane. This happens still following the concentration gradient , so particles move using the protein from an area of high concentration to an area of low concentration.
Now how about if something doesn't want to follow the concentration gradient and wants to instead go from an area of low concentration to an area of high concentration? Then active transport occurs. This requires energy.
Hope this helps 
Edit : beaten by cosine   

[TheAspiringDoc]

Hello everyone! 

I would just like to ask if anybody could explain the modes of transport of soluble substances across the plasma membrane. And explain each of the following: Simple diffusion, facilitated diffusion, osmosis and active transport.

Thanks.

Okay to start us off, diffusion is the movement of molecules down the concentration gradient. What this means is that the molecules are moving from a region of high concentration to a region of lower concentration.

If this diffusion refers to the movement of water, then we call this osmosis.

If the diffusion is of anything else (i.e. only refers to solute molecules) then it's just diffusion (which can have added bits tacked onto the name (e.g. simple)

Because the molecules in diffusion are moving down the concentration gradient (a.k.a. from a region of high concentration of the molecule to a region of lower concentration), they will do it with out needing any energy input.

Simple diffusion occurs when a molecule (which has to be non-polar as the fatty tails of the phospholipid bilayer will not all ow polar molecules to pass through - the exception to this is water, which although polar, can occasionally just slip through because it's soooo tiny)  basically just passes in between the phospholipids that constitute the cell membrane.

Facilitated diffusion is the same as simple diffusion, except the molecule passing through (such as glucose or water) has to pass through a protein channel which 'facilitates' (helps) it. This also requires no energy input as again, it is simply diffusion. Water, for example, most commonly passes through a protein channel known as an aquaporin. I'm not sure about this next bit I'm about to say, so could someone please verify? But I also believe that this aquaporin can be shut if the cells wishes (well cells don't 'wish' ), meaning that the cell won't absolutely fill up with water and lyse (burst/explode) if it is placed in pure water as otherwise the water would move in to balance the concentration of all the stuff inside the cell compared to the outside. Right?

As I've said earlier, osmosis is simply the diffusion of water across the semi-permeable membrane. Again, it is diffusion, so it doesn't require any expenditure of energy. This can be seen for example when you have the classic 'U-shaped' container thing (guys, what's it called LOL with a semi-permeable membrane in the centre-bottom bit, in which the SP membrane is permeable for water, but not salt. If there are different concentrations of salt on either side, then the water will move (diffuse) from the area of lower concentration of the salt (as this is the area with the higher concentration of the water) to the area of lower concentration of the salt. This is osmosis in action!
(google osmosis - the image I've described should come up)

Active transport also refers to the movement of molecules across semi-permeable membranes, but the molecules are moved 'up' their concentration gradient (imagine there were two pools of equal size; one pool had 5 ppl in it and the other had 10. People would be moving up the concentration gradient if even more people from the less populated pool moved to the more populated one). For this reason, active transport requires the expenditure of energy (which is sourced from the breakdown of ATP into ADP + Pi [Pi just means a free phosphate]).

Basically all this movement across the cell membrane ideally intends to allow the cells to take in and get rid of what it needs (although am I forgetting things like endo and exocytosis?)

Endocytosis is the movement of larger, non-soluble molecules into the cell via a process in which a part of the phospholipid bilayer forms a vesicle configuration around the thing being moved based on the same principles of hydophilia/phobia that cause them to generally form the cell membrane. Exocytosis is the same, but isthe movement of the molecules out of the cell. Both of these DO require energy expenditure.

An example of exocytosis is when neurotransmitters move out of the axon of one neuron via exocytosis, diffuse across the synapse (so they go down the concentration gradient) and then reach the dendrite of the receiving neuron, and then activate a postsynaptic receptor to continue the series of things but that's nerves so eh imma stop soon

Also interesting to know that the organelles inside a (eukaryotic) cell are also membrane bound (as that's pretty much the definition of a eukaryotic cell) so they too are involved in some of these forms of transport.

I hope this is helpful (As mr andersen says [watch his video on movement across cell membranes!!!!!!!!!! {Bozeman Bio}])



EDIT: Haha I lose *raspberry @ cosine & sunshine*

[TheAspiringDoc]

Heyo

Can someone please outline the purpose of the non-template strand of DNA?
(I mean if it doesn't even code for RNA, what use is it?)

Thanks!

[cosine]

Heyo

Can someone please outline the purpose of the non-template strand of DNA?
(I mean if it doesn't even code for RNA, what use is it?)

Thanks!

I am assuming you're talking about RNA transcription, right?
Well, no, in terms of VCE Biology, the non-template strand is not used to code for RNA, but it has to exist - because remember, the original DNA molecule is double stranded, and because RNA is single stranded, then only one strand of the DNA double helix could possibly be used to transcribe the RNA.

Im not sure if this directly answers your question - bit of a vague one haha, 'what use is it' xD