L10- Membrane transport Flashcards
What is a membrane?
A thin pliable layer of tissue covering surfaces, enveloping a part or separating or connecting structures or organs
What is the structure of membranes?
- Phospholipid bilayer with polar head groups (hydrophilic) and hydrophobic fatty acid tails made of hydrocarbons.
- Hydrophilic surface and hydrophobic core of bilayer
What are the major lipid components of biological membranes?
• Glycerophospholipids • Sphingolipids • Glycosphingolipids • Glycoglycerolipids All contain glycerol attached to phosphates in head groups and fatty acid tails
What are integral membrane proteins?
Largely buried within the membrane but are usually exposed on both faces
What are peripheral membrane proteins?
Exposed at only one membrane face
Have oligosaccharides attached to their membrane proteins that project into the aqueous surroundings of the cell
What does it mean if a protein is glycosylated?
It means it is found in the membrane (facing out)
What is the fluid mosaic model?
Lateral movement within the phospholipid bilayer occurs but diffusion across the membrane is slow
What is the transition temperature of a membrane?
The temperature at which a phospholipid bilayer changes from the (solid) gel state to crystalline liquid state
What does the Tm depend on?
The nature of the hydrocarbon tails (saturated or unsaturated) and the head groups.
Unsaturated hydrocarbon tails have lower melting points than saturated phospholipid
How can organisms protect membranes from thermal stress?
Alteration of membrane lipids to maintain optimal conditions at a given temperature
What are key characteristics of integral membrane proteins?
- High percentage of hydrophobic residues, particularly in parts embedded in membrane
- Segments of protein that span the membrane are alpha helical
What are the ways in which transport occurs across membranes?
- Simple diffusion
- Carrier-mediated transport
- Endo/exocytosis
What are examples of hydrophobic molecules?
Easily diffuse through membrane
O2,CO2,N2, benzene
What are examples of small uncharged polar molecules?
Mostly diffuse through membrane
H2O, urea, glycerol
What are examples of large uncharged polar molecules?
Some diffuse through membrane
Glucose, sucrose