Plasma Membranes Flashcards
Name 4 roles of cell-surface membranes
1- Compartmentalisation
2- Chemical reactions
3- Cell signalling
4- Controls which molecules can enter or leave a cell/organelle
What is compartmentalisation?
The formation of separate membrane bound area
It’s vital in order to:
- Separate ant reactions that are incompatible
- Allows for formation of specific conditions within the area surrounded by the membrane
- Allows for the creation of chemical gradients
- Protects cell components
What is cell signalling?
- Cells in multicellular organisms need to communicate to coordinate their response
- Protein has a specific tertiary (3’) structure, e.g. hormones
- Protein bonds to specific receptor with complementary tertiary structure on cell membrane
- Activate a response
What is the structure of cell-surface membranes?
- Formed from a phospholipid bilayer: hydrophilic phosphate heads form both the inner and outer layer of a membrane, the fatty acid tails form a hydrophobic core inside the membrane
- Cells normally exist in aqueous environments. Phospholipid bilayers are perfectly suited as the hydrophilic heads can interact with water
What molecules can diffuse through the phospholipid bilayer?
Small, non-polar molecules, e.g. CO2, O2
Describe and explain the ‘fluid mosaic model’ of membrane structure
- The phospholipids are free to move within the layer relative to each other (they are fluid), giving the membrane flexibility
- The proteins embedded in the bilayer vary in shape, size and position (in the same way as mosaic tiles)
What are intrinsic proteins?
Give 2 examples
Transmembrane proteins that are embedded through both layers of a membrane
Channel and carrier proteins
What are channel proteins?
- A transport protein
- Allows passive movement of small polar molecules down a concentration gradient
- E.g. ions, Na+, K+, Ca+
What are carrier proteins?
- A transport protein
- Allows passive and active movement of large molecules
E.g. carbohydrates
What are glycoproteins?
- Intrinsic proteins
- They are embedded in the cell-surface membrane with attached carbohydrate chains
- Cell signalling
What are glycolipids?
- Lipids with attached carbohydrate chains
- These molecules are called cell markers and can be recognised by the cells of the immune system as self or non-self.
What are extrinsic proteins?
Present in the one side of the bilayer
What is cholesterol?
- A lipid
- Binds to hydrophobic tails
- Makes membrane more rigid/less flexible
- Strength and support (animal cells don’t have a cell wall)
- It regulates the fluidity of membranes
How does temperature affect membrane structure?
Freezing: -10°C
- Carrier proteins + protein channels lose shape and open
- Cell membrane damaged by ice crystals
- Membrane is very permeable
Cold: 0°C
- Low KE
- Phospholipids close together
- Membrane is stiff
- Least permeable
Warm: 20°C
- phospholipids have more KE
- More movement
- More space between them
- More permeable
Hot: 40°C +
- Carrier proteins + protein channels denature
- Open
- Phospholipid bilayer melts
- Membrane is very permeable
How do solvents affect membrane structure?
- Some solvents can dissolve the phospholipids in the membrane
- E.g. ethanol
- Loses it’s structure
- Increases it’s permeability