Membranes

• Partially permeable membrane • Act as barrier between cell + environment. • Substances move across plasma membrane through: osmosis, AT + diffusion • Allow cell recognition + cell communication.

All composed of lipids, proteins + carbohydrates.

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.

• 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.

Hydrophilic ——> head of phospholipids = negative phosphate –> attracts to water Hydrophobic ——> tail of the phospholipids repels water

Cholesterol = stability • Low temperatures = cholesterol binds to hydrophobic tail —> pack more closely together = less fluid. • High temperatures = phospholipids not packed closely together—-> more fluid.

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.

• 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.

• 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.

• Phospholipid bilayer = melt -> membrane = more permeable. • Water inside cells expand .: pressure placed on membrane. • Channel/carrier proteins in membrane denature. –>Increases permeability of membrane.

• Phospholipids = move around, aren’t packed as tightly together. • Partially permeable membrane. • Phospholipids = more kinetic energy–> increases permeability of membrane.

• Increasing concentration of solvent –> increases membrane permeability. • Organic solvents dissolve membrane –> loses its structure. (alcohols -> antiseptic wipes) • Affects transmission of nerve impulses.

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.

• 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.

• Lipids with carbohydrate chain attached. • Cell markers/antigens • Can be recognised by immune system as self or non-self.

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.