The Cell Membrane Flashcards
What are the general functions of cell membranes?
Continuous, selective permeability barrier
Control of enclosed chemical environment Communication
Recognition signalling molecules
Signal generation in response to stimuli
Examples of signalling molecules?
Adhesion protein
Immune surveillance
What is the composition of membranes in dry weight?
40% lipid
60% protein
1 to 10% carbohydrates
What are the ranges of fatty acid chains?
C14-C24 and C16-C18
Examples of phospholipid head groups?
Choline
Define
Ethanolamine
Inositol
What is a sphingomyelin?
(Sphingolipids) it’s the only other phospholipid with a phosphate in the membrane.
What is a liposome? Their use?
An enclosed structure.
Delivery of drugs
What are cerebrosides and gangliosides?
Cerebrosides- head group sugar monomer Gangliosides- head group oligosaccharide (sugar multimers)
What are the different types of phospholipid motion?
Flexion
Rotation
Lateral diffusion
Flip-flops
What are the influences of cis double bonds in the bilayer structure?
Unsaturated hydrocarbons chains with sis double bonds reduce phospholipid packing increasing the fluidity
What is the structure of cholesterol?
Polar had a group, rigid planar steroid ring structure. Non polar (flexible) hydrocarbon tail. Hydroxyl head group
What is the significance of the hydrogen bond between the
Reduces mobility and motion therefore reducing the fluidity
What is the paradoxical effect of cholesterol?
Reduced phospholipid chain motion reduces fluidity.
Reduced phospholipid packing increases fluidity
What are lipid rafts?
Dynamic cholesterol rich structures comprised of sphingolipids with saturated fatty acid chains and tightly integrated cholesterol
What is the function of lipid rafts?
Signalling scaffolds which allows dimerisation of signalling pathways
What are the two types of evidence for proteins in membranes?
Functional- facilitated diffusion
Biochemical- freeze fracture and gel electrophoresis
What is freeze fracture and two faces?
Fracturing a crystal with a knife, between two membrane lamella. P fracture face and E fracture face.
What is SDS?
A detergent that coats all proteins with a negative charge so they move in the same direction during a gel electrophoresis.
What are the three modes of mobility of proteins in the bilayer?
Confirmational change
Rotational
Lateral
Why can’t proteins flip-flop?
The amount of hydrophilic structure that is exposed to the aqueous environment is too big and too energetically unfavourable to flip across the membrane
What are the restrictions of proteins in the bilayer?
Membrane protein associations
Association with extramembranous proteins
Lipid mediated effects
What are the two main membrane proteins and their features?
Peripheral they have electrostatic and hydrogen bonds interactions, removed by changes in pH or in ionic strength
Integral they interact extensively with hydrophobic domains of the bilayer, removed by agents that compete for nonpolar interactions
What are transmembrane polypeptide composed of?
Small, hydrophobic, polar and charged amino acids R groups. Alpha helical domains.
What is a hydropathy plot?
To check for membrane proteins
