Quick question - trans fats and membrane fluidity?

[040111333]

I'm confused on this simple question: Do trans fats increase or decrease membrane fluidity? The Kaplan Biochem. book seems to have a contradicting answer, so I wasn't sure

---

Members don't see this ad.

 

[Astra]

Trans fats are unsaturated fatty acids.

Unsaturated fatty acids increase membrane fluidity and therefore, trans fats will increase fluidity.

 

[040111333]

Trans fats are unsaturated fatty acids.

Unsaturated fatty acids increase membrane fluidity and therefore, trans fats will increase fluidity.

Hmm, but trans fats are made from the hydrogenation of unsaturated fatty acids right? Kaplan says this: Part of the health concern of trans fats is due to their ability to lower membrane fluidity, in addition to the tendency of trans fats to accumulate and form plaques in the bloodstream.

Thoughts? I thought it might be because hydrogenation makes the double bonds single again in trans fats? hence decreasing the kinks in the cell membrane and therefore, decreasing fluidity overall?

 

[aldol16]

Hmm, but trans fats are made from the hydrogenation of unsaturated fatty acids right? Kaplan says this: Part of the health concern of trans fats is due to their ability to lower membrane fluidity, in addition to the tendency of trans fats to accumulate and form plaques in the bloodstream.

Thoughts? I thought it might be because hydrogenation makes the double bonds single again in trans fats? hence decreasing the kinks in the cell membrane and therefore, decreasing fluidity overall?

Trans fats are not made from hydrogenation. Trans fats have a trans double bond - that's why they're called trans fats. Hydrogenation of an unsaturated fatty acid would saturate the alkene carbons, removing the double bond altogether. Alkane carbons don't have trans or cis configurations because they are free to rotate. Trans fats decrease membrane fluidity because they pack similarly to saturated fats - that is, all they're missing is 2 hydrogen atoms. They pack similarly. The reason cis fats increase fluidity is because they introduce kinks in the membrane.

 

[Astra]

Trans fats are not made from hydrogenation. Trans fats have a trans double bond - that's why they're called trans fats. Hydrogenation of an unsaturated fatty acid would saturate the alkene carbons, removing the double bond altogether. Alkane carbons don't have trans or cis configurations because they are free to rotate. Trans fats decrease membrane fluidity because they pack similarly to saturated fats - that is, all they're missing is 2 hydrogen atoms. They pack similarly. The reason cis fats increase fluidity is because they introduce kinks in the membrane.

Is this image correct? The cis fats are V shaped and therefore would introduce kinks?

https://qph.is.quoracdn.net/main-qimg-a5e067decfb245bc722e8872ce58be94?convert_to_webp=true

 

[Phoodie]

Is this image correct? The cis fats are V shaped and therefore would introduce kinks?

https://qph.is.quoracdn.net/main-qimg-a5e067decfb245bc722e8872ce58be94?convert_to_webp=true

Yup

 

[Astra]

Yup

So in terms of membrane fluidity,

Cholesterol increases fluidity

saturated fats decrease.

Cis fats increase

Trans fats decrease

Correct? Also, anything else related to fluidity I am missing?

 

[Phoodie]

So in terms of membrane fluidity,

Cholesterol increases fluidity

saturated fats decrease.

Cis fats increase

Trans fats decrease

Correct? Also, anything else related to fluidity I am missing?

Yeah I'm pretty sure that's all correct. Nothing else is really coming to my mind right now so

 

[BerkReviewTeach]

The key thing here is to consider what you are increasing or decreasing from. In terms of the impact on cell membrane fluidity, you need to consider the packing of the structures.

Alkanes pack more tightly than alkenes, making them more "solid like" (with a higher mp). Cell membranes with saturated fats will exhibit the least fluidity.

Trans-alkenes pack more tightly than cis-alkenes, making them more "solid like" (with a higher mp). Cell membranes with trans-alkenes (trans fats) will exhibit reduced fluidity compared to cis-alkenes fats, but more fluidity than saturated fats.

So trans fats reduce cell membrane fluidity if they replace cis-fats, but increase cell membrane fluidity if they replace saturated fats.

 

[aldol16]

Cholesterol increases fluidity

Yeah I'm pretty sure that's all correct. Nothing else is really coming to my mind right now so

Cholesterol works both ways: http://www.cholesterol-and-health.com/Cholesterol-Cell-Membrane.html

It's better to use first principles to reason these out than to memorize them.

 

[Astra]

Cholesterol works both ways: http://www.cholesterol-and-health.com/Cholesterol-Cell-Membrane.html

It's better to use first principles to reason these out than to memorize them.

Let me make sure I understand the reasoning.

Cholesterol lowers membrane fluidity by reducing the interactions between the phospholipids and leading to more fluidity.

Cholesterol increases membrane fluidity by allowing the membrane to be heated to higher temperatures before the membrane becomes extremely fluid?

Cholesterol is sorta like a buffer then lol?

 

[NextStepTutor_3]

Sure! If I remember correctly, Khan's membrane fluidity video actually compares cholesterol to a buffer. At low temps, it introduces space between the fatty acid tails, which would otherwise clump together; at high temps, it attracts the tails and limits the increase in fluidity that would occur if it weren't present.