The structure of Cell Membrane Flashcards
Cell membranes are most made of
Lipids
What two types of membrane can you have in eucaryotic cells
Cell membrane/ Plasma membrane
Internal membranes
Cell Membrane/ Plasma membrane
Boundry between the cell and internal environment
The absolute barrier for eucaryotic cells
Surrounded by cell wall
About 5nm thick
Interface to the external world.
Contains many proteins used for good function
- Receiving info
- Import and export of molecules
Internal Membrane
Membranes that separate the organelles from the cytoplasm
What is the structure of the membrane
Lipid Bilayer
Combination of lipids and proteins
This is intersperses with intercalated proteins- These proteins control the membrane functions
What is special about the lipids in the membrane
They are phospholipids
Amphipathic property
Both hydrophobic and hydrophilic
What is special about the lipids in the membrane
Amphipathic property
Both hydrophobic and hydrophilic
This helps membranes assemble spontaneously. Don’t need enzymes/ enzyme catalysis to bring them together
Which ends of the lipids face where
Hydrophilic ends face the water
(either the external environment or the cytoplasm)
Hydrophobic ends face the inside
This is why the lipid layer is a double layer
This is the most energetically favourable conformation
Hydrophilic
Dissolve readily in water due to charged atoms or polar groupd that form electrostatic/ hydrogen bonds with water molecules
Hydrophobic
Insoluble because their atoms are uncharged.
They force water molecules to form a cage like structure around the molecule.
The tails can be either
Saturated or Unsaturated (contains double bonds )
Therefore the hydrophobic end can either be saturated or unsaturated
What is and what causes a self sealing layer
Forces involved in bilayer formation
Membrane damage is energetically unfavourable and leads to repair of vesicle formation
Repair occurs to small damages
Large damage is fixed by creating a vesicle
Membrane movement
They are in constant motion and are said to be fluid
What are each of the layers in the lipid bylayer called
Leaflets
Lipids move constantly within their own leaflet. How do they move between leaflets (flip flop)
Flip flop occurs spontaneously very rarely
Axis rotation and lateral diffusion are common and frequency is related to temperature
Why is having high blood cholesterol bad
Cholesterol as a molecule can integrate itself into the lipid bilayer within blood vessels. Stops lipid movement –> blood vessels loose their fluidity and become more rigid and start to get inflamed
Are the leaflets symmetrical
There is asymmetry in the leaflets.
Glycolipids
Lipids that have short stretches of carbohydrates attached to them.
Never found in the inner lipids only in the outer lipids
Leaflet that faces the extra cellular environment
Predominance of phosphotodile prolein
single myline
Cholesterol
Have glycolipids
When does asymmetry in lipids arise
Arises during manufacture
Lipids are manufactures in the endoplasmic reticulum. This has enzymes that produce lipid components. These are first integrated into the leaflet that faces the cytoplasm.
Scramblases flip some of the lipids
The bilayer then leaves the endoplasmic reticulum and moves as vesicles to the golgi apparatus. In the golgi apparatus the flippases move the specific lipids either to the cytoplasmic to extracellular sides
Scramblases
Facilitate the flip flop so the bilayer grows evenly
Present in the endoplasmic reticulum
More random
Only faciliate extention of the lipid membrane
The different lipids are differentiated how
Separated based on what their different polar groups are
Flippases
Present in the golgi apparatus
More to do with which specific membrane faces which way
there are three ways proteins can be localised on membranes
Transmembrane
Lipid attached
Protein attached
Transmembrane proteins
Proteins that spanned the entire membranes
Lipid Attached Protein
Proteins that face either the internal or external environment. Attached to the lipids in the lipid bilayer
What are the two types of membrane protein
Integral - Have to use a harsher treatment and break open the lipid membrane
Peripheral - Easily extracted, leave the membrane in tact
This is dependent on how hard it is to extract from the membrane
What are the two types of membrane protein
Integral - Have to use a harsher treatment and break open the lipid membrane
Peripheral - Easily extracted, leave the membrane in tact
This is dependent on how hard it is to extract from the membrane
The extremely hydrophobic nature of the space between the leaflets means what for proteins
The water molecules in the proteins are repelled so the proteins are forced to fold in specific ways. Forming alpha helixes and beta barrels
What are the differences between alpha helixes and beat barrels
Alpha helixes are tighter wound and beta barrels are larger.
Alpha helixes tend to be receptors- Don’t allow movement of molecules across a membrane but have a role in sensing the internal environment.
Beta barrels are larger and allow the movement of molecules across a membrane
How do we disrupt a bilayer
Use detergents e.g. SDS –> Form mycells
Breaks lipids apart
Cell Cortex
The membrane is very fluid and fragile
The cell cortex provides the shape.
Protein framework that is attached to the lipid membrane
Fibrous meshwork of proteins attached to the cytosolic side
Within the membrane can proteins move
Yes
The cells have a specific way of controlling this movements.
Cells restrict the movement of proteins by creating barriers . Especially in the gut
How to cells control protein movement
1.Tethering proteins to the cell cortex
2. Tethering to the extracellular matrix proteins
3. Tethering to proteins on the surface of another cell
By falling within a diffusion barrier
