Plasma Membranes Flashcards
(37 cards)
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
What is simple diffusion?
Net movement of molecules from high to low concentration down a concentration gradient
What factors affect the rate of diffusion?
- Temperature
- Concentration difference
How does temperature affect the rate of diffusion?
- Higher temps increase KE
- More movement
- Increases rate
How does concentration gradient affect the rate of diffusion?
The steeper concentration gradient, the faster the rate of diffusion
What factors affect the rate across membranes?
- Surface area
- Diffusion distance (thickness of membrane)
How does SA affect the rate of diffusion across membranes?
The larger the surface area, the faster the rate of diffusion
How does the thickness of the membrane affect the rate of diffusion across a membrane?
The shorter the diffusion distance the faster the rate of diffusion
What is facilitated diffusion?
Net movement of molecules from high to low concentration down a concentration gradient through a channel protein
What is active transport?
The net movement of particles from an area of low concentration to an area of high concentration against a concentration gradient requiring ATP and using carrier proteins
