Biological Membranes Flashcards
Describe the fluid mosaic model?
Fluid- phospholipid bilayer in which individual phosphlipids can move, the membrane has a fixed shape.
Mosaic- extrinsic and intrinsic proteins of different sizes and shapes embedded.
What is the role of cholesterol in membranes?
Steroid molecule in some plasma membranes, connects phospholipids and reduces fluidity to make bilayer more stable
What is the role of glycolipids in membranes?
Cell signalling and cell recognition
What are the functions of extrinsic proteins?
Binding sites/ receptors e.g. for hormones and drugs
Antigens (glycoproteins)
Bind cells together
Involved in cell signalling
What is the role of intrinsic proteins?
Electron carriers (respiration/ photosynthesis) Channel proteins (facilitated diffusion) Carrier proteins (facilitated diffusion/ active transport)
What is the function of membranes within cells?
Provide internal transport system
Selectively permeable ti regulate passage if molecules into/ out of organelles or within organelles.
Provide reaction surface
Isolate organelles from cytoplasm for specific metabolic recations.
What is the function of the cell-surface membrane?
Isolates cytoplasm from extracellular environment.
Selectively permeable to regualte transport of substances
Involved in cell signalling/ cell recognition
What are the factors that affect membrane permeability?
Temperature- high temperature denatures membrane proteins/phospholipid molecules have nore kinetic energy and move further apart.
pH- changes tertairy structure of membrane proteins
Use of a solvent- may dissolve membrane
What is osmosis?
Water diffuses across semi-permeable membranes from an area of higher water potential to an area of lower water potential until a dynamic equilibrium is established.
What is water potential?
Pressure created by water molecules measured in kPa
What is simple diffusion?
A passive process that requires no energy from ATP hydrolysis.
Net movement of small, lipid-soluble molecules directly through the bilayer from an area of high concentration to an area of lowe concentration, down a concentration gradient
What is facilitated diffusion?
A passive process.
Specific channel or carrier proteins with complementary binding sites transport larger and/or polar molecules/ ions (not soluble in hydrophobic phospholipid tail) down a concentration gradient
How do channel proteins work?
Hydrophilic channels bind to specific ions. One side of the protein closes and the other opens.
How do carrier proteins work?
Binds to complementary molecules. Conformational change releases molecue on the other side of the membrane; in facilitated diffusion, passive process, in active transport, requires energy from ATP hydrolysis
What is active transport?
ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape.
Specific carrier protein transport molecules/ions from an area of low concentration to an area of higher concentration (against the concentration gradient)
