2B-Cell Membranes Flashcards
Cell membranes
- partially permeable and control which substances enter or leave the cell
Fluid mosaic model
Phospholipids form a double bilayer, channel proteins, carrier proteins , glycolipids and glycoproteins, receptor proteins on cell surface membrane and cholesterol
Phospholipids in cell membranes
Hydrophobic fatty acid tails face in so doesn’t allow large and water soluble substances (ions and polar molecules) but small non polar substances can diffuse across
Cholesterol
A lipid that gives Membrane stability and bonds to hydrophobic fatty acid tails of phospholipids causing them to pack more closely together- makes more rigid -has hydrophobic regions barrier to polar substances and maintains cell shape
Why blood cells have cholesterol
Membranes stability as free floating so maintains shape
Temperature below zero affect on membranes
- phospholipids little energy so don’t move much. -close together so membrane rigid. -channel proteins and carrier denature increasing membranes permeability -ice crystals pierce membrane - permeability increases
Temp of zero to 45
- phospholipids more mobile not tightly packed - partially permeable As temp increases phospholipids move more increasing permeability
Temp of 45 above affect on membranes
Bilayer melts - increasing permeability - water inside cell expands puts pressure on membrane -proteins denature increasing permeability
Simple diffusion
Passive process net movement of particles from an area of high conc to low conc across a partially permeable membrane down a conc gradient until equilibrium is established
Factors affecting diffusion rate
1- conc gradient size. 2-thickness of exchange surface. 3- surface area
Facilitated diffusion
Passive - net movement of particles from area of high concentration to low conc across a channel or carrier protein until equilibrium is reached
What uses facilitated diffusion
Large and charged polar particles and ions
Carrier proteins
1- Large molecule attaches to carrier protein in membrane 2- protein changes shape 3- releases molecule on opposite side f membrane
Channel proteins
Pores in membranes for charge particles to diffuse through
Factors affecting facilitated diffusion rate
1- conc gradient size. 2- number or channel or carrier proteins