Membrane fluidity - EK 1001 Bio

[09grad]

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Hey guys, can someone help me with this question: pg 45 of EK 1001 bio.


At what temperature would you expect the ratio of unsaturated to saturated fatty acids to be the LOWEST?

A. 10 C
B. 20 C
C. 30 C
D. 40 C

The answer says A.

But my thinking was D, since unsaturated fatty acids promote fluidity, and this is least necessary at higher temperatures. If its cold, the membrane tends to be rigid, so you'd expect more unsaturated fatty acids at colder temps.

Their explanation is this: "According to the passage, increase in temp will cause an increase in both fluidity and fatty acid unsaturation. Therefore, the unsaturated/saturated fatty acid ratio will be lowest at the lowest temp".

Thanks

 

[loveoforganic]

I'm so confused.

 

[09grad]

by what?

 

[loveoforganic]

unsaturated and saturated fa's are interconverting?

 

[Velocity]

Hey guys, can someone help me with this question: pg 45 of EK 1001 bio.


At what temperature would you expect the ratio of unsaturated to saturated fatty acids to be the LOWEST?

A. 10 C
B. 20 C
C. 30 C
D. 40 C

The answer says A.

But my thinking was D, since unsaturated fatty acids promote fluidity, and this is least necessary at higher temperatures. If its cold, the membrane tends to be rigid, so you'd expect more unsaturated fatty acids at colder temps.

Their explanation is this: "According to the passage, increase in temp will cause an increase in both fluidity and fatty acid unsaturation. Therefore, the unsaturated/saturated fatty acid ratio will be lowest at the lowest temp".

Thanks

I think you answered it yourself. As you said, unsaturated fatty acids promote membrane fluidity. But the membrane becomes more rigid at cold temperatures. Why? Saturated fatty acids. You're taking it a step further and saying that the cell would try to counteract this by doing the reverse, but in doing so you're ignoring what you already know. (Or so it seems to me.)

I'm not 100% confident of that explanation but it seems reasonable to me.

 

[BellJS]

something about this strikes me as odd. Especially because it is a well known fact that animals in the arctic carry a high ratio of unsaturated to saturated fatty acids (that's why we love them for their omega-3's unsaturated fatty acids).

 

[maanya88]

Hi,

I am in cell biology right now and we were just tested on this stuff.
Basically, the bilayer is at 37 degrees Celsius. If the temp decreases (lets say 25 degrees for example) then the number of unsaturated fats increases and the amount of cholesterol decreases.
Conversely, if the temp increases (45 degrees for example), then the number of saturated fats and the amount of cholesterol in the bilayer increases.
Think of the temperature not as cold or hot but as the phase transition temperature. In the first scenario, we can melt the membrane at 25 degrees because the bonds are weak due to the increased fluidity '(greater number of unsaturated fatty acids)...the opposite is true for the second example.
Hope this helps 🙂

 

[unique135]

I must say none of the above explanations clearly make sense to the point.

I searched over couple of books and internet. I haven't found anything that could agree with EK's answer. Even its explanation is wierd; I couldn't find anywhere in the passage that increase temperature causes increase in FA unsaturation (maybe someone can help me figure that out).

I think EK's original answer is wrong. Correct answer should be D.

 

[BellJS]

I must say none of the above explanations clearly make sense to the point.

I searched over couple of books and internet. I haven't found anything that could agree with EK's answer. Even its explanation is wierd; I couldn't find anywhere in the passage that increase temperature causes increase in FA unsaturation (maybe someone can help me figure that out).

I think EK's original answer is wrong. Correct answer should be D.

very true. I was trying to use a real world example that probably came off as useless at best.

the answer is clearly wrong because an increase in temp only increases fluidity via a mechanism that probably isn't worth describing, but it doesn't inherently increase unsaturation. Cells must maintain a relatively constant fluidity, this is accomplished by increase unsaturation:saturation to counter the decrease in temps, and an increase in saturation:unsaturation( the lowest unsat:sat) to counter increases in temperatures.

 

[soby10]

The answer is A

b/c some plants and bacteria such as cyanobacteria are able to alter the membrane composition of sat to unsat fatty acids as a way to acclimate to the cold temp. Genes are activated to produce sat fats and repress unsat fats kind of like "heat shock" stress singnaling. Here's a link that may explain it in further detail http://www.jstor.org/pss/4277965.

The point is the membrane is not static but fluid. Like the cell overall it reacts to the environment. Phospholipids move laterally and in some rare situations flip-flop, cholesterol is added in animals to decrease the membrane from being too fluid ect.

 

[unique135]

The answer is A

b/c some plants and bacteria such as cyanobacteria are able to alter the membrane composition of sat to unsat fatty acids as a way to acclimate to the cold temp. Genes are activated to produce sat fats and repress unsat fats kind of like "heat shock" stress singnaling. Here's a link that may explain it in further detail http://www.jstor.org/pss/4277965.

The point is the membrane is not static but fluid. Like the cell overall it reacts to the environment. Phospholipids move laterally and in some rare situations flip-flop, cholesterol is added in animals to decrease the membrane from being too fluid ect.

I skimmed the article. I could only conclude that unsaturated fatty acids increase to restore the membrane fluidity that was originally reduced by low temperature. D sounds right to me.

 

[soby10]

I was reading the question and passage again yes your right increasing unsat will increase fluidity and (previous typo) "genes are activated to produce unsat fats and repress sat fats in cold temps in certain organisms" thus D would be correct and its true deep sea animals have more unsat fats than sat. So scientifically D would support this as does the article link.

But reading the passage "According to the passage, increase in temp will cause an increase in both fluidity and fatty acid unsaturation." It didn't say they are talking about deep sea animals or plants therefore we can't assume that. But it does say increase temp=more unsat therefore the biggest disparity in ratios is there at high temps and thus the smallest disparity in ratios is in the opposite cold temps.
Although i agree i think scientifically that is incorr but based solely on the passage i would chose A.
This seems to be a good verbal question not a bio quest as no real science is tested just semantics.

 

[Econ2MD]

"So I can clearly not choose the glass in front of me."

This debate reminds me of The Princess Bride.

From a chemistry pov, I would think unsaturated fats are higher energy species and would be less likely to form at low temps...so I can clearly not choose d 😉

 

[unique135]

But reading the passage "According to the passage, increase in temp will cause an increase in both fluidity and fatty acid unsaturation." It didn't say they are talking about deep sea animals or plants therefore we can't assume that. But it does say increase temp=more unsat therefore the biggest disparity in ratios is there at high temps and thus the smallest disparity in ratios is in the opposite cold temps.
Although i agree i think scientifically that is incorr but based solely on the passage i would chose A.
This seems to be a good verbal question not a bio quest as no real science is tested just semantics.

If you read the article, 2nd para "When poikilothermic organisms such as bacteria..." agrees with what I said. increase temp=more unsat ....I think this is wrong.

"I would think unsaturated fats are higher energy species and would be less likely to form at low temps...so I can clearly not choose d 😉

I would appreciate if you can discuss this a bit further.


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Source: EK Forums

User:
1. the cell stay alive by keeping itself balanced ( homeostasis) thus. at low temperature the cell would want to increase memebrane fluidy where as at high temperature the cell would want to decrease membrane fluidity

with that said. when ratio of unstrated vs saturated is high -> it causes a more fluid membrane. when the ratio is low -> it causes a lower fluid membrane. so, when the ratio is low, the cell must be encountering a high temperature.

Dr. Johnson:
That is correct. This is an edit they never incorporated.

 

[MDJerome]

Good thing I did a search. I just encountered this problem and I believe that the answer is incorrect. As the temperature decreases, cell membranes increase unsaturated fatty acids in the bilayer to increase the fluidity of the membrane. Otherwise, the cell would become ridgid. It doesn't make sense to say that a cell at high temperature (that's already fluid) will increase its number of unsaturated fatty acids. If anything it would decrease the unsaturated fatty acid count at higher temperatures to maintain steady fluidity.

Can anyone explain if this is wrong or right.

 

[Prateek]

Good thing I did a search. I just encountered this problem and I believe that the answer is incorrect. As the temperature decreases, cell membranes increase unsaturated fatty acids in the bilayer to increase the fluidity of the membrane. Otherwise, the cell would become ridgid. It doesn't make sense to say that a cell at high temperature (that's already fluid) will increase its number of unsaturated fatty acids. If anything it would decrease the unsaturated fatty acid count at higher temperatures to maintain steady fluidity.

Can anyone explain if this is wrong or right.

I'm thinking the answer should be D as well

As temperature decreases, unsaturation INCREASES, therefore the ratio of unsaturated:saturated will increase

As temperature increases, unsaturation DECREASES, therefore the ratio of unsatured:saturated will decrease

 

[sangria1986]

I'm thinking the answer should be D as well

As temperature decreases, unsaturation INCREASES, therefore the ratio of unsaturated:saturated will increase

As temperature increases, unsaturation DECREASES, therefore the ratio of unsatured:saturated will decrease

I think an easy way to think about is to look at the fats we eat....

At fats that are solid at room temp have greater amount of unsaturated fats (think butter-they have less fluidity but also are more stable) However, melted butter has lost its unsaturation and become saturated-at higher temperatures.

If you think about it...fats stored in organisms would likewise be converted to unsaturated fats in colder temps because they are more stable at those temps...whereas at higher temps, the saturated fats are more stable.

 

[whiteshadodw]

there is a reason i don't tend to put too much confidence in EK 1001. quite a few errata, and this question took me and my gf almost 20 minutes to figure out...until she pointed me to this page. LOL love EK.

 

[user12]

im starting to think examkrackers are full of crap for a lot of their explanations. many are loaded with errors.