Lecture 5 – Lecture Notes
- Bilayers form spontaneously because of hydrophobic tails.
- The left tail is saturated while right tail is unsaturated in the picture above.
- Can have many sites of unsaturation (carbon-carbon double bonds)
- Lots of unsaturated, more fluidity.
- Lots of saturated and packed tightly, less fluidity.
Importance of unsaturation:
- Saturated, linear molecules are acted on by desaturase.
- Manipulating desaturase abundance can help manage membrane fluidity. - Many desaturase enzymes, because some will want a little unsaturation and
some may want a lot of saturation. Some desaturases could work at different
temperatures. **Enzymes differ in where the double bond will take place.
- if small and uncharged, easy to get through, large and very charged, hard to
- Nonpolar molecules just diffuse down concentration gradient.
- Ions need to be transported across because they can’t readily diffuse across. - Membrane proteins transport molecules across membranes.
- Many alphahelises minimizes the charges of the protein backbone. So it can
interact with hydrophobic s acid tails.
- Membrane proteins have tell-tail signature of where active site is, nonpolar,
uncharged amino acids at active site.
- Diffusion down a concentration gradient, less of the molecule. Driven by
free energy change. More ability to do work when there are more molecule
on one side than the other.
- Facilitating diffusion: using protein pore or channel allowing lots of molecule
to transport through membrane. Some pores only allow one at a time.
Channel allows much more molecules.
- Active transport: pumping things against concentration gradient. Moving
molecule from low concentration to higher concentration. Against free
energy change, need energy to do this. ABC transporters (group of
molecules) are active transporters.
- Different transporters transport different things.
Modeling a neuron:
- Ions diffuse along electrochemical gradients.
- Not just chemical (how much of each on both sides of membrane) but
electrical (what charge on each side).
- Equilibrium doesn’t mean same concentration of molecu