L7: Biological Membranes Flashcards
What is the main function of the plasma membrane?
Separates the intracellular and extracellular environments, to form a layer of protection against the exterior environment
What components make up the plasma membrane?
-Composed of lipids (mainly phospholipids ) and proteins
- There are two opposing sheets of lipids into which proteins are inserted
- Each lipid has a hydrophobic tail (interior of membrane) and a hydrophilic head (exterior of membrane) which defines the lipid bilayer structure
What are some other functions of the plasma membrane?
- Separates the intracellular and extracellular environments
- Involved in cell signalling by receiving information via receptors on the proteins in the plasma membrane
- Flexible to give cells the capacity to move and expand
What is the fluid mosaic model?
The phospholipid bilayer with proteins integrated within the spaces between phospholipids
What are the functions of membrane proteins?
Cell signalling, communication and selectively permeable
What are the main phospholipids found in the plasma membrane?
- Phosphatidylcholine
- Sphingomyelin
- Phosphatidylserine
- Phosphatidylethanolamine
What other lipids are found in the plasma membrane?
- Cholesterol
- Glycolipids
What is the structure of a phospholipid?
- Non-polar, hydrophobic tail (hydrocarbon)
- Polar, hydrophilic head containing a glycerol and phosphate group
- Head group attached to the phosphate to form a specific phospholipid e.g. choline for phosphatidylcholine
What term is used describe a phospholipid?
Amphipathic (having both hydrophobic and hydrophilic regions)
What section of the phospholipid interacts with what region?
- The hydrophilic head interacts with the intracellular and extracellular environments of the cell
- The hydrophobic tail is in the centre and forms a bilayer to do so
What is the difference between saturated and unsaturated fatty acid tails?
- Saturated tails contain no double carbon bonds
- Unsaturated tails contain double carbon bonds
What is the effect of a double bond in the fatty acid tail?
- Creates a kink in the tail which affects the ability to pack into the plasma membrane
What makes up a molecule of glycerol?
3 carbons
1 hydroxyl group
How are the fatty acid chains attached to the glycerol?
2 hydroxyl groups attached to the fatty acid chain by ester linkage
How is phosphate attached to the glycerol?
Phosphodiester bond
What charge does phosphatidylcholine have?
- Neutral charge due to one positive and negative charge
- Still means that it is highly hydrophilic
How does sphingomyelin different to the other phospholipids?
- Does not have a glycerol
- Has sphingosine instead
- Same in every other way
What charge does phosphatidylserine have?
- Negative charge - has 2 negative and 1 positive
- Overall negative charge
What is the composition of the phospholipid bilayer?
- Inner and outer monolayers have different compositions
- Predominantly phosphatidylcholine with sphingomyelin on the extracellular leaflet
Predominantly phosphatidylserine with phosphatidylethanolamine on the intracellular leaflet