Membranes Flashcards
(16 cards)
What is the function of a cell surface membrane?
- Partially permeable membrane
- Act as barrier between cell + environment.
- Substances move across plasma membrane through: osmosis, AT + diffusion
- Allow cell recognition + cell communication.
What is contained the structural molecule?
What is the structure of membranes?
All composed of lipids, proteins + carbohydrates.
Made in 1972
Describe the fluid mosaic model?
Describes arrangement of molecules in the membrane.
Phospholipids form a continuous, double layer –> bilayer.
‘Fluid ‘ —-> phospholipids constantly moving.
Proteins scattered through bilayer, –> tiles in a mosaic.
Describe the component: phospholipids
- Barrier to dissolve water substances.
- Centre of bilayer = hydrophobic water-soluble substances (ions/polar molecules) cannot diffuse through membrane.
- Fat soluble substances dissolve in bilayer + pass directly through the membrane.
What do the terms hydrophobic and hydrophilic mean in terms of phospholipids?
Hydrophilic ——> head of phospholipids = negative phosphate –> attracts to water
Hydrophobic ——> tail of the phospholipids repels water
What molecule controls the fluidity of the bilayer?
Cholesterol = stability
- Low temperatures = cholesterol binds to hydrophobic tail —> pack more closely together = less fluid.
- High temperatures = phospholipids not packed closely together—-> more fluid.
Difference between intrinsic and extrinsic proteins?
Intrinsic—> embedded through both layers of membrane
e.g: channel/carrier proteins.
AA with hydrophobic R group that interact with hydrophobic core of membrane
Extrinsic—>only present one side of bilayer.
Hydrophilic R groups in outer surfaces that interact with polar heads of phospholipids.
What is the function of membrane within cells?
- Divide cells into different **compartments. **
- Act as a barrier between organelles + cytoplasm.
- Form vesicles –> transport substances between different areas of cell.
- Partially permeable to control what enters/exits.
- Membranes within organelles act as a barrier between the membrane contents + rest of organelles.
How does low temperature affect membrane permeability?
- Low energy, can’t move around.
- Channel proteins + carrier proteins in membrane denature –> increasing permeability of membrane.
- Ice crystals form + pierce membrane.
- Highly permeable when it thaws.
How does high temperatures affect membrane permeability?
- Phospholipid bilayer = melt -> membrane = more permeable.
- Water inside cells expand .: pressure placed on membrane.
- Channel/carrier proteins in membrane denature.
–>Increases permeability of membrane.
How does normal temperature affect membrane permeability?
- Phospholipids = move around, aren’t packed as tightly together.
- Partially permeable membrane.
- Phospholipids = more kinetic energy–> increases permeability of membrane.
How do solvents affect membrane permeability?
- Increasing concentration of solvent –> increases membrane permeability.
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Organic solvents dissolve membrane –> loses its structure.
(alcohols -> antiseptic wipes) - Affects transmission of nerve impulses.
What are the roles of glycoproteins?
Intrinsic proteins.
Embedded on CSM with attached carbohydrate chain.
Role:
- Cell adhesion (cells join together to form tight junctions in certain tissues)
- Receptors for chemical signals.
How are glycoproteins involved in cell signalling?
- Chemical binds to receptor ~> elicits a response.
- Direct response or a cascade
- Acts as receptor for neurotransmitter at nerve cell synapse.
- Acts as receptor for peptide hormones (insulin/glucagon) ~> affect uptake + storage of glucose.
Describe role of glycolipids
- Lipids with carbohydrate chain attached.
- Cell markers/antigens
- Can be recognised by immune system as self or non-self.
Practical: Investigating the effect of temperature and organic solvents on membrane permeability.
When beetroot membrane = disrupted, red pigment is released to surrounding solution.
Amount of pigment released = disruption of cell membrane.
Absorbance of each sample measured using colourimeter with blue filter.
