VCE Biology Question Thread

[TheAspiringDoc]

Ok another few questions I'm not sure about...

Which of the following activities is not found in all living cells?
A. movement
B. aerobic respiration
C. growth
D. synthesis

I'm thinking B or D?...

Amino acids contain four chemical groups connected to a central carbon atom. Which of the following atoms or groups of atoms is not connected to the central carbon in all amino acids?
A. NH2
B. COOH
C. CH3
D. H

I had no idea for this one, never came across this scenario before..

Which of the following is not a function of protein molecules found in the membranes of cells?
A. They act as channels for the transport of lipid soluble molecules
B. They act as receptor sites for some signalling molecules
C. They facilitate the diffusion of charged particles
D. They are the site of active uptake of glucose molecules.

I'm thinking the answer is D? But I'm not sure.


Thanks again for all the help!!

EDIT: Just saw TheAspiringDoc's last post:
Well I felt that since the quaternary structure is all the molecules joining with other molecules in the form of strands of amino acids, they would be interacting with each other and that might cause the structure of the protein to be the way that it is.

Well the first one is almost certainly B. I'm not sure what sunshine's reasoning is?
for the second one, therre sure ain't no CH3 in an amino acid (google a.a. structure )
third one's A. lipid soluble molecules go through the cell membrane.

[sunshine98]

Well the first one is almost certainly B. I'm not sure what sunshine's reasoning is?
for the second one, therre sure ain't no CH3 in an amino acid (google a.a. structure )
third one's A. lipid soluble molecules go through the cell membrane.

I was looking at it as all cells have the potential to respire aerobically - they just need oxygen to do so. But not all cells can move , cause that's dependent on like the presence of flagellas and not all cells have that

[geminii]

Well the first one is almost certainly B. I'm not sure what sunshine's reasoning is?
for the second one, therre sure ain't no CH3 in an amino acid (google a.a. structure )
third one's A. lipid soluble molecules go through the cell membrane.

I see, thanks so much!
Haha yeah the second one was quite simple, I just didn't look at the question carefully

A-I'm thinking A, because not all cells have flagellas which is what allows movement.
B- most cells can perform it. Aerobic respiration is dependent on oxygen not something that the cell contains
C- cell cycle is something that all cells undergo , where growth is a part of one of the stages
D- All cells synthesis things  particularly proteins , that's why prokaryotes have ribosomes.
Answer is  C. If you search up an image of a typical amino acid and you will see that it has all the rest attached.A is the answer because they act as channels for water soluble molecules not lipid soluble. Lipid soluble will usually diffuse through if its along the concentration gradient
Hope this helps

Thank you, this helps a lot!

I was looking at it as all cells have the potential to respire aerobically - they just need oxygen to do so. But not all cells can move , cause that's dependent on like the presence of flagellas and not all cells have that

But don't all cells just move around? Like they aren't stuck in one place right?

[TheAspiringDoc]

I was looking at it as all cells have the potential to respire aerobically - they just need oxygen to do so. But not all cells can move , cause that's dependent on like the presence of flagellas and not all cells have that

You can move without flagella. Some cells even exhibit a "crawling" motion owing to changes in the shape of their cytoskeleton.

[sunshine98]

You can move without flagella. Some cells even exhibit a "crawling" motion owing to changes in the shape of their cytoskeleton.

Did a google search and this seems to be correct , but some yahoo answer says there are some plant cells that don't move..idk. imma leave this for the T-rav to answer.

[vox nihili]

Did a google search and this seems to be correct , but some yahoo answer says there are some plant cells that don't move..idk. imma leave this for the T-rav to answer.

Can definitely move without flagella. Some will use cilia (tiny flagella), many will—as AspiringDoc said—deform their shape and basically shapeshift in a particular direction, others will blow out water and propel themselves along

[peridotleaves]

although B does look kinda sensible, A is pretty promising. As wiki says "The interactions and bonds of side chains within a particular protein determine its tertiary structure."

I was under the impression that the amino acid sequence helps determine the tertiary structure, but it often still needs to be modified by chaperonins etc

[nerdgasm]

Hey everyone, I'm having trouble with a few multiple choice questions. I'll post one now and then post the others later to give people a chance to answer.

The three-dimensional structure of a protein
A. is determined by its sequence of amino acids
B. varies depending on the interaction of the protein molecule with other molecules
C. is irrelevant to the function of the protein molecule
D. is determined by the active site

I'm torn between A and B but leaning more towards A, so any help would be much appreciated! Thanks

I agree with Mr. T-Rav here; both A and B both appear to be correct. The sequence of amino acids in a protein definitely has significant influence on the 3-D structure, because of interactions between different atoms in those amino acids (in short, primary structure influences secondary structure which influences tertiary structure). Not any 3-D structure will do - there will be attractions and repulsions from all the atoms in the protein, and generally, you want structures that have less 'strain' on the atoms. Another point is that the active site in proteins is usually due to a particular sequence of amino acids (e.g. an active site may be formed by having many amino acids which become negatively charged when placed in the body's natural environment, allowing the protein to form favourable interactions with other molecules).

However, once the protein is formed, its 3-D structure can certainly be altered by interactions of the protein with other molecules. An explicit example of this would be haemoglobin, whose 3-D structure will alter depending on how many oxygen molecules it is carrying. Also, by the 'induced fit' model of enzyme-substrate interactions, there can be slight alterations to the structure of an enzyme when a substrate is bound to it. Another example can be found in the various types of enzyme/protein inhibition.

Therefore, I definitely think both A and B make sense; I'd be more inclined to go with B since the sequence of amino acids is not the *only* thing which determines the 3-D structure of a protein (but honestly, I don't think the question is very well designed).

If I've said anything wrong, please correct me (it's been 5 years since I did Bio 3/4!)

[vox nihili]

I was under the impression that the amino acid sequence helps determine the tertiary structure, but it often still needs to be modified by chaperonins etc

I agree with Mr. T-Rav here; both A and B both appear to be correct. The sequence of amino acids in a protein definitely has significant influence on the 3-D structure, because of interactions between different atoms in those amino acids (in short, primary structure influences secondary structure which influences tertiary structure). Not any 3-D structure will do - there will be attractions and repulsions from all the atoms in the protein, and generally, you want structures that have less 'strain' on the atoms. Another point is that the active site in proteins is usually due to a particular sequence of amino acids (e.g. an active site may be formed by having many amino acids which become negatively charged when placed in the body's natural environment, allowing the protein to form favourable interactions with other molecules).

However, once the protein is formed, its 3-D structure can certainly be altered by interactions of the protein with other molecules. An explicit example of this would be haemoglobin, whose 3-D structure will alter depending on how many oxygen molecules it is carrying. Also, by the 'induced fit' model of enzyme-substrate interactions, there can be slight alterations to the structure of an enzyme when a substrate is bound to it. Another example can be found in the various types of enzyme/protein inhibition.

Therefore, I definitely think both A and B make sense; I'd be more inclined to go with B since the sequence of amino acids is not the *only* thing which determines the 3-D structure of a protein (but honestly, I don't think the question is very well designed).

If I've said anything wrong, please correct me (it's been 5 years since I did Bio 3/4!)

nerdgasm's reasoning is completely right


For those who are still a little unsure and feel like they need definitive proof. A is correct because of something called the Afinsen principle/dogma. Without getting bogged down in the details, this idea came out of work done by a bloke named Christian Afinsen, who basically found that protein folding is contingent on the primary structure (i.e. amino acid sequence) of the protein. In essence, what he showed is that if you unfold a protein and then expose it to a particular set of conditions the protein will refold into the same structure. This therefore indicates that 3D structure of the protein is not determined by the environment, but rather, by the amino acid sequence. One way to look at it is to acknowledge that the environment facilitates the folding of a protein into its shape. The environment can either permit it or not. But at the end of the day, the protein still has a shape that it wants to fold into.

B is right as well because proteins have an enormous capacity to change shape based on their interaction with other proteins. ALL of you should already know this. This is exactly what the induced fit model relates to. Substrate binds, protein changes shape. Boom, interaction with molecule leads to changed shape of protein.

[mahler004]

I was looking at it as all cells have the potential to respire aerobically - they just need oxygen to do so. But not all cells can move , cause that's dependent on like the presence of flagellas and not all cells have that

Not true - oxygen is toxic to some anaerobic bacteria.

[geminii]

Just saw this on the internet, as well as in my teacher's notes:

"Scattered in the lipid bilayer are cholesterol molecules, which help to keep the membrane fluid consistent."

I was under the assumption that cholesterol in the membrane decreases its fluidity/flexibility and makes it harder, and when there is too much cholesterol the membrane becomes impermeable and rigid. Is this correct? Does the above quote mean the same thing as what I'm thinking? Clarification would be appreciated!

Thanks!

[Injustice]

Just saw this on the internet, as well as in my teacher's notes:

"Scattered in the lipid bilayer are cholesterol molecules, which help to keep the membrane fluid consistent."

I was under the assumption that cholesterol in the membrane decreases its fluidity/flexibility and makes it harder, and when there is too much cholesterol the membrane becomes impermeable and rigid. Is this correct? Does the above quote mean the same thing as what I'm thinking? Clarification would be appreciated!

Thanks!

Cholesterol in the bilayer actually does both. When temperatures are above optimal, the cholesterol actually prevents the bilayer from liquifying, and makes it more rigid. When temperatures are lower than optimal, the cholesterol actually prevents solidification of the bilayer.

[geminii]

Cholesterol in the bilayer actually does both. When temperatures are above optimal, the cholesterol actually prevents the bilayer from liquifying, and makes it more rigid. When temperatures are lower than optimal, the cholesterol actually prevents solidification of the bilayer.

Thank you!

I also have another question... are lipids all triglycerides, with the only variation being the molecule at the top which is usually choline? AKA do all molecules have a glycerol molecule, three fatty acids and a phosphate molecule? Or only some?

[Gogo14]

Thank you!

I also have another question... are lipids all triglycerides, with the only variation being the molecule at the top which is usually choline? AKA do all molecules have a glycerol molecule, three fatty acids and a phosphate molecule? Or only some?

Can some explain to me what choline is?

From my reading so far no. Triglycerides does not have a phosphate molecule. It is glycerol molecule plus 3 fatty acids. Phosopholipids is similar to triglyercides, but one of the fatty acid chains is replaced by a phosophate molecule. Also, there are steriods which are another type of lipid.

[Injustice]

Thank you!

I also have another question... are lipids all triglycerides, with the only variation being the molecule at the top which is usually choline? AKA do all molecules have a glycerol molecule, three fatty acids and a phosphate molecule? Or only some?

Not all lipids are triglycerides. Just think of lipids as fats/oils. All lipids (fats/oils) are composed of fatty acids and a glycerol backbone, all of them. How many fatty acids, depends on what type of lipid it is! I will put it this way, a glycerol backbone is the 'neck' of all lipids (fats/oils), and this backbone, only have three available bonds (slots) to join with. So, in triglycerides (tri = 3), there are three fatty acid chains attached/bonded to the backbone, which is the glycerol molecule. So triglycerides have 1 glycerol molecule and 3 fatty acid chains attached to it. Now, with phospholipids, a phosphate group gets attached to one of the slots/bonds available on the glycerol backbone, and remember, there are a maximum three slots available. So as the phosphate group is attached, there are only two more slots left. So these two slots are occupied by two fatty acid chains. So finally, phospholipids have 1 glycerol backbone, 1 phosphate group and 2 fatty acid chains bonded to the glycerol backbone.