The phospholipid head is the end that likes water
- The idea
- Predict
- See it
- Why
- Check
The idea
“The tails love water and the head avoids it, so the heads hide in the middle of the membrane.”
Hydrophilic and hydrophobic look almost the same on the page. The long tails also look like the part that would reach into the water.
The short version
The mistake: The tails love water and the head avoids it, so the heads hide in the middle of the membrane.
What's actually true: The polar phosphate head is hydrophilic and faces water. The nonpolar fatty acid tails are hydrophobic and hide.
- Water is polar, so it's drawn to charged groups. The phosphate in the head is negatively charged, which makes the head hydrophilic.
- The fatty acid tails are carbon and hydrogen. C-H bonds are nonpolar, so water can't hydrogen bond with them, and the tails are hydrophobic.
- A molecule with a hydrophilic end and a hydrophobic end is amphipathic. Water sits on both sides of a cell membrane, so it takes two layers.
On the exam: The phosphate head faces water and the fatty acid tails hide. If tails touch water, you flipped it.