B4 Transport Across Cell Surface Membrane Flashcards
What are plasma membranes?
All membranes around and within all cells
What are cell surface membranes?
Plasma membranes that surround cells and form boundaries between cell cytoplasm and the environment
What functions do phospholipids have in cell surface membranes?
Allow lipid soluble substances to enter and leave the cell; prevent water soluble substances entering and leaving; make membrane flexible and self sealing
Whats the general structure of the phospholipid bilayer?
Hydrophilic phosphate head on outside; hydrophobic hydrocarbon tail on inside
How are proteins embedded in the phospholipid bilayer?
surface of bilayer, never extend completely across, act as mechanical support; Completely span the bilayer, protein channels, carrier proteins
What are the functions of the proteins in the cell surface membrane?
Mechanical support; channels transporting water soluble substances across membrane; allow active transport via carrier proteins; cell surface receptors for identifying cells; help cells adhere together; receptor for hormones
What are the functions of cholesterol in the phospholipid bilayer?
reduce lateral movement of molecules including phospholipids; make membrane less fluid at high temp; prevent leakage of water and dissolved ions from cell
What are the functions of glycolipids in the membrane?
recognition sites; maintain stability of membrane; help cells attach to each other and form tissue
What are glycolipids made of?
Carbs covalently bonded with a lipid
What are the functions of glycoproteins in a membrane?
Recognition sites; help cells attach to each other to form tissues; allow cells to recognise one another , eg lymphocytes
Why can molecules not freely diffuse between the cell surface membrane?
Molecules are : insoluble in lipids, cant pass phospholipid bilayer; too large; same charge as protein channels, repelled; electrically charged, cant pass through non polar hydrophobic tail
What are the functions of the membrane within the cell?
control entry and exit of material in discrete organelles such as mitochondria and chloroplasts; separate organelles from cytoplasm; provide internal transport system; isolate enzymes that may damage cell; provide surfaces on which reactions can occur
Why is the fluid mosaic model of the cell surface membrane called that?
FLUID : individual phospholipid molecules can move relative to one another , membrane is flexible and constantly changing shape; MOSAIC : proteins embedded in phospholipid bilayer vary in shape, size, pattern
What is the definition of diffusion?
Net movement of molecules or ions from region of higher concentration to a region of lower concentration until evenly distributed
What increases the rate of diffusion?
Steeper concentration gradient, higher temperature - more kinetic energy, larger surface area, non polar smaller molecules, thinner exchange surface
