Sodium-Glucose Transport 2 (PDF)

## B2.1 Membranes & Membrane Transport ### Membrane fluidity - Depends on the type of fatty acids and cholesterol between the phospholipids - Membranes must be sufficiently fluid to allow many of its functions but not too fluid as it must also control what can pass through. #### Unsaturated fatty...

## B2.1 Membranes & Membrane Transport ### Membrane fluidity - Depends on the type of fatty acids and cholesterol between the phospholipids - Membranes must be sufficiently fluid to allow many of its functions but not too fluid as it must also control what can pass through. #### Unsaturated fatty acids: - Fatty acid chains - If saturated = straight => can pack together - More solid in room temp. - Ie. has a higher melting point - Unsaturated fatty acids, bends in their chains => harder to pack => increase in fluidity - Ie. lower melting point - **Arctic fish:** What composition of fatty acids do they have? - More unsaturated fatty acids compared to fish in warmer water ### Cholesterol - Ringed lipid molecule - Amphipathic - Hydrophobic tail - interacts with the phospholipid tails - Hydrophilic part - interacts with the phospholipid heads. - **Cholesterol** regulates membrane fluidity by acting as a modulator - At high temp. cholesterol binds to phospholipids => prevents them from being too fluid => stabilizing - At low temp. cholesterol prevents phospholipids from packing too densely => increasing fluidity ## B2.1.1 Membrane Structure: Fluid Mosaic Model - **Phospholipids** - **Integral membrane protein** - **Cholesterol ** - **Peripheral protein** Proteins in the membrane can have different functions: **Integral proteins** - Have both hydrophilic and hydrophobic parts - Ie. protein channels for facilitated diffusion - Protein pumps for active transport **Peripheral proteins** - On the surface of the membranes, either facing the outside or the inside of the cell. - Can function as: - Hormone receptors - Neurotransmitter receptors - Immobilised enzymes. **Glycoproteins** - Have chains of sugars (oligosaccharides) attached. - These function as cell recognition "identity flag" = antigens. ### Membrane Transport - Efficient barrier that controls what goes in & out - How can substances pass across the membrane? - **Passive transport** - no energy required - **Simple diffusion** - the passive movement of particles from a higher conc. to an area of lower conc. => along the conc. gradient until the conc. is equal everywhere - **Facilitated diffusion** - **Osmosis** - **Active Transport** - energy (ATP) required #### Passive transport - **Simple Diffusion** - Only small, non polar & non-charged particles can diffuse between the phospholipids: - O2 (oxygen gas) - CO2 (carbon dioxide) - Always from a higher to a lower conc. - Small, charged or polar particles cannot pass across the membrane. - **Salts** Na+, K+, Cl-, Ca2+ => charged, must diffuse through channel proteins in the membrane - **Osmosis** ## D2.3 Osmosis **Hypotonic** - **Hypertonic** - Water moves from a hypotonic solution to a hypertonic solution to even out the conc. of free-moving water molecules. - Continues until equilibrium on both sides. - This is diffusion: - No energy required - Along the conc. gradient **Animal cells vs. Plant cells** **Animal cells** - No cell wall - Have cell membrane - Unicellular organisms have contractile vacuole to regulate osmotic condition: - Osmosis => contractile vacuole - Multicellular animals (humans) don't have this **Plant cells** - Cell wall - Have cell membrane on the inside of the wall - Have large vacuole. ### Osmolarity - Measure of solute conc. in a litre of water - **Hypertonic** - High conc of solutes - **Hypotonic** - Low/no conc of solutes - **Isotonic** - Same conc of solutes on both sides of a membrane