Cell Membranes Flashcards
What is cellularity?
Universal property of life
What is the basic structure of a membrane?
Thin (5nm) film of lipids and proteins held together by non-covalent interaction
The lipid bilayer forms an impermeable barrier to water soluble/ polar molecules
What are the 3 types of membrane lipid?
Glycerophospholipids - Glycerol molecules is bonded to 2 fatty acids and a phosphate group which is bonded to an R group.
Sphingolipids - 2nd carbon is bonded to an amine group - only contain saturated fatty acids so are straight
Sterols- cholesterol - Rigid part made of rings which are connected to a polar head group and a non- polar hydrocarbon tail which decreases membrane fluidity
Outline the link between thermodynamics and the lipid bilayer
Polar molecules dissolve- increased entropy
Non polar molecules dont dissolve - water molecules form an ice like cage structure around the molecule which decreases entropy
How is a lipid bilayer formed?
Hydrophobic tails cluster together
The edges of the bilayer then meet to form a continuous spheroid and a sealed compartment
How do cells respond to damage to their membranes?
Phospholipids are created in the cell
What is the fluid mosaic model?
Fluid - lipids can move in the layer
Mosaic - Different shapes and sizes of molecules
What are the 3 main methods of fluidity?
Lateral diffusion - phospholipids move around within the layer
Flexion - movement of the tail
Rotation- aids membrane function
What are the regulators of membrane fluidity?
Unsaturated double bonds - as they dont pack together tightly and make the membrane thinner
Cholesterol - Decreases membrane fluidity as phospholipids cant move laterally but they prevent them from compacting and becoming too rigid
What are lipid rafts?
Randomly distributed with mainly sphingolipids as they have long fatty acid chains and strong attractive forces to hold adjacent molecules together, and cholesterol - proteins are recruited in this area which increases the efficiency of processes
What are glycoproteins and glycolipids?
Proteins and lipids that are bonded to a carbohydrate
These created the CHO coating of the membrane called the glycocalyx which is protective
What are the membrane proteins?
Integral/ transmembrane proteins- single pass and multi pass
Peripheral membrane proteins -
embedded within the layer or covalently bonded to a lipid or non covalently attached to integral membrane proteins
What is the difference between integral and peripheral membrane proteins?
Integral cross the entire membrane from outer to inner layer (multi pass cross multiple times)
whereas
Peripheral do not cross the entire membrane
What 2 factors impact transport across the membrane?
Size and charge/ polarity of the molecule
State the molecules and how easily they can move across the membrane
No problem - non polar molecules
Ok - Small uncharged polar molecules
Probably - Large uncharged polar molecules
Not at all - charged, large and polar / ions
What are all transport proteins?
Trans multi pass proteins
What are carrier proteins?
Bind a solute and undergo a conformational change to transfer across the membrane
What are channel proteins ?
Interact only weakly with solute, form aqueous pore that solutes can pass through quickly - selective - size and charge of the ion thus only allowing the correct ions through
What is facilitated diffusion?
Movement of a solute down a concn gradient through a partially permeable membrane
What is passive transport?
No energy required
Simple diffusion
Channel mediated
Carrier mediated
What is the electrochemical gradient?
If an ion has a charge then concn and charge determine the direction of flow
e.g. +ve ions outside of the membrane will be attracted to the negative charge on the inside whereas -ve ions will be attracted to the outside
What is active transport?
Pumping solutes across a membrane against their concn gradient which requires energy e.g. energy from electrons transfer
What are coupled carriers?
Secondary active transport
Symporters - move 2 solutes in the same direction- one down its concn gradient which releases energy for the other solute to move against its gradient
Antiporters- do the same but move them in different directions
What are ATP driven pumps?
Primary active transport
e.g. Na+k+ ATPase pump - free energy released by ATP hydrolysis to actively pump 3 Na+ out of the cell and 2K+ into the cell
What are the different types of channel proteins?
Voltage gated - change in membrane potential to open the gates
Ligand gated channels - Only opened by the binding of a ligand
Mechanically gated - disruption in the membrane causing the gate to open
