Cell Membranes and Transport

• What are the two main components of a cell membrane? phospholipids and proteins
• Is the fatty acid of a phospholipid hydrophobic or hydrophillic? hydrophobic
• is the phosphate group of a phospholipid hydrophobic or hydrophillic? hydrophillic
• what are intrinsic proteins? proteins that span the membrane from one side to the other
• what are extrinsic proteins? founds inside the bilayer or on the surface
• What do the hydrophilic and hydrophobic portions of the protein depend on? The location of the R group in the primary sequence
• what is the cell membrane described as? selectively permeable to non-polar molecules e.g oxygen, fat-soluble molecules e.g vitamins, non charged molecules and small molecules
• What do the R groups lining the space down the middle of a channel protein do? Makes them specific to charged or polar particles allowing them to diffuse across the membrane in facilitated diffusion
• what are all the carbohydrates projecting outside of the cell called? glycocalyx
• what is the glycocalyx involved in? cell recognition, act as specific antigens
• what do the molecules of cholesterol do? regulate the fluidity of the membrane
• what happens if there is not enough cholesterol? membrane becomes too fluid
• what happens if there is too much cholesterol? membrane becomes too rigid
• what did Singer and Nicolson put forward? the fluid mosaic model
• what does 'fluid' in fluid mosaic model refer to? the lateral movement in the membrane
• what does 'mosaic' refer to in 'fluid mosaic model'? the random pattern of the proteins
• How did Singer and Nicolson provide evidence for the fluidity of hte membrane? - From the fusion of two cells - They had two cells one where the membrane proteins were labelled with red dye and the other labelled with green dye - After an hour the red and green dyed proteins dispersed evenly across the membrane proving the lateral movement in the membrane
• Beetroot experiment - cylinders of beetroot are cut to 1cm length, controls surface area - cylinders are rinsed to wash away pigment from damaged cells - cylinders are placed in tubes of water of 5cm^3 then placed in a thermostatically controlled water bath at 20 degrees celcius - after 30 mins the tubes of water are removed and beetroot removed - place the tube of water in a colorimeter to measure absorbance of light - repeat experiment with temperatures at 30,40,50
• What happens are temperatures below 40 in the beetroot experiment? - increases kinetic energy - causes phospholipids and proteins to move more - creates gaps between phospholipids - pigment will also have more kinetic energy - pigment will diffuse out of the cell through gaps
• what happens at temperatures above 40 in the beetroot experiment? - protein compnents of the membrane begin to denature - forms pores which pigment diffuses out of - graph will level off as all proteins denature since membrane becomes fully permeable to pigment
• what is diffusion? random movement of particles from a region of high concentration to a region of low concentration
• what is passive transport? doesnt requrie ATP/energy from respiration
• what is rate of diffusion dependent on? - surface area of the membrane - length of diffusion pathway - steepness of concentration gradient - temperature - membrane permeability, can be affected by salt, presence of detergents and organic solvents
• what is facilitated diffusion? larger molecules that are too big to cross the membrane by facilitated diffusion or charged molecules and polar molecules transported through protein carriers
• what is osmosis? net movement of water from an area of high water potential to low water potential across a selectively permeable membrane
• what is water potential? tendency of water to leave a system by osmosis
• water and solute potential are always... negative values
• pressure potential is always a.... positive value
• what is hypotonic? a hypotonic solution has a lower solute concentration so therefore a higher water potential
• what is hypertonic? has a higher concentration of solutes and a lower water potential
• what is haemolysis? when the blood cells expand and burst because of increased pressure in the cells
• what is crenating? water goes out the blood cell and the cells shrivel
• what happens to blood cells in an isotonic solution? no net movement of water
• what is the equation showing the relationship between solute,water and pressure potenial? Ψw = Ψs + Ψp
• what does it mean if a plant cell is turgid? water enters by osmosis and the cytoplasm and vacule expand and its not physically possible for any more water to enter the cell
• what is plasmolysis in plant cells? water leaves the cells by osmosis and the vacuole and cytoplasm shrink because of loss of water and the cytoplasm pulls away from the cell wall
• what is incipient plasmolysis? the point where 50% of the cells are plasmolysed so water potentials of solution and tissue are equal