Chapter 6: 6.2 Membranes Flashcards
Different membranes have different —– ——–
Lipid profiles
What are membranes made up of?
A variety of lipids and proteins
What do the membrane compositions represent?
Represents a fluid mosaic model
What diffuses rapidly throughout the plane of the membrane?
Lipids
True or False:
In membranes, protein composition is always the same
False, protein composition is random
Protein are able to travel ——— throughout the membrane
Laterally
What forces are involved in membrane lipid assembly?
- Hydrophobic effect
- Van der Waals forces
Different lipids yield different membranes, what lipid shapes are there?
- Cone
- Cylinder
Why do polar lipids aggregate?
To minimize contact between water and their hydrocarbon chains
What do cone shaped lipids form?
Micelles
What do cylinder shaped lipids form?
Bilayers
What does membrane fluidity depend on in the membrane?
Lipids within the membrane
List:
Properties of lipids that affect membrane fluidity
- Saturation
- Hydrocarbon length
- Cholesterol
- Headgroup
Define:
Tm
Phase Transition Temperature
* Midway point between gel-like and fluid membranes
Describe:
Structure of membrane hydrocarbons as it moves from solid to fluid
Hydrocarbons chang from anti-conformation to gauche conformation resulting in more “kinks”
What R Groups affect Tm?
- Choline
- Ethanolamine
- Glycerol
True or False:
The longer the chain length, the higher the Tm
True
The tighter the packing of the kipids…
The more solid the membrane
At lower temperatures, membranes have more…
Unsaturated hydrocarbon chains
At higher temperatures, membranes have more…
Saturated hydrocarbon chains
What does cholesterol act as in membrane fluidity?
Cholesterol acts as a “buffer”
What does it mean that cholesterol acts as a “buffer”?
It disrupts lipid packing as well as provides rigidity
Describe:
High Temperature Adaptations of Hypothermophilic Archaea
Have a lipid called caldarchaeol
* Stabilizes the membrane even more at high temperatures
What high temperature adaptations are present on hydrocarbons chains?
Hydrocarbon chains are linked with glycerol at both ends
Describe:
Membrane Lipid Dynamics
Lipids move laterally in the membrane very rapidly (1 μm/s)
* Transverse diffusion is much slower
Why is transverse diffusion so much slower?
The polar head group does not easily pass through the hydrophobic interior
In transverse diffusion:
What move lipids from the outer membrane to the inner membrane?
Flippases
In transverse diffusion:
What moves lipids from the inner membrane to outer membrane?
Floppases
In transverse diffusion:
What transports lipids from either side of the membrane to the other?
Scramblases
Define:
FRAP
Fluorescence Recovery After Photobleaching
State:
Steps of FRAP
- Fluorescently label lipids
- Bleach membrane
- Monitor how quickly fluorescence returns
What does FRAP show?
Show that lipids rapidly diffuse laterally
Describe the process of:
Freeze Fracture EM of the Membrane
- Freeze cells to -196°C in liquid nitrogen
- Fracture membrane )opens along interface of lipids)
- Separate the two halves
- Make a carbon-metal replica of each half
- Observe via electron microscopy (EM)
What can freeze fracture EM of the membrane show?
Shows that membrane protein distribution is random
Describe the process of:
Single Molecule tracking of Phospholipids/proteins
- Label phospholipid/protein
- Place in a live kidney (contains compartments)
- Track with microscope
What can single molecule tracking of phospholipids/proteins?
Shows that lipids diffuse quickly and freely between compartments, but protein remained contained within compartments longer
What can diffusion be impeded by? (4)
- Actin cytoskeleton barriers on the underside of membrane
- Organelle membranes contacting the plasma membrane
- Extracellular matrix linked to the membrane proteins
- Immobile membrane protein and lipid clusters
