What are the characteristics of phospholipids?

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Discussion Overview

The discussion revolves around the characteristics of phospholipids, particularly focusing on their headgroups and hydrocarbon chains. Participants explore the classification of phospholipids as amphipathic, polar, or non-polar, and the implications of pH on their charge and behavior.

Discussion Character

  • Homework-related
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that phospholipid heads are both charged and polar, while the tails are non-polar.
  • Others argue that at low pH, phospholipids may become uncharged, raising questions about their amphiphilic nature.
  • A participant notes that the pKa of phosphoric acid suggests it is dissociated at physiological pH, leading to a negatively charged anion.
  • There is a suggestion that the charge of the phosphate group depends on pH, while polarity remains constant.
  • Some participants question whether there is a single correct answer to the classification of phospholipids, indicating that multiple interpretations may exist.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the classification of phospholipids, with multiple competing views regarding their characteristics and the influence of pH on their charge and polarity.

Contextual Notes

The discussion highlights the dependence of phospholipid characteristics on pH, which introduces uncertainty regarding their classification as charged or uncharged, polar or non-polar.

Kushal
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Homework Statement



Phospholipids have headgroups and hydrocarbon chains as follows:

A. amphipathic, non polar
B. non polar, polar
C. polar, non polar
D. charged, non polar


Homework Equations



phospholipids have a phosphate head group and fatty acid residue hydrocarbon tails.


The Attempt at a Solution



I have eliminated A and B as they are obviously incorrect.

I would classify phospholipid heads as being both charged, and (thus) polar.

C and D seem to be, both, correct answers to me.

But of course there should be only one.
 
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Answers C and D are not incorrect. At what pH would the negatively charged phosphate be protonated (and uncharged)? If you were at that pH, would the phospholipid act as an amphiphile?
 
The answer is not A
 
since phosphoric acid is a weak acid, it's pKa should be between 2 - 6.

Therefore at physiological pH 7.4, the acid will be dissociated, giving the negatively charged anion.

Am I correct?

If, the pH is very low, in strongly acidic conditions, then the phospholipid will be uncharged.
 
At that low pH would answer D apply? There is a more correct answer (independent of pH).
 
Using the Le Chatelier's Principle, then there will be no charge on the phosphate because it would remain undissociated!

Is that it?

ooo but then, the charge will depend on the pH, while, the polarity will always be here!

so, in a sense, it is better to say C!

right?
 

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