Lecture 4 Flashcards
What are the functions of the biological membranes?
Defines boundaries and compartmentalizes organelles; compartmenst allow for localization of specific proteins, so unique functions for organelles; regulate the movement of molecules; contains receptors for signals allowing cell-cell communication
What are phospholipids made from?
Two fatty acids attached to a glycerol backbone with a phosphate head
What are fatty acids?
Hydrocarbon chains with a COO- (carboxylic acid) at one end
What is the difference between saturated and unsaturated fatty acids?
Saturated has no C=C double bonds, unsaturated does (causes kinks)
Name the three important properties of the biological membrane
Hydrophobic core acting as permeability barrier, stable and self-healing, provides sealed and closed compartments
Name the classes of amphipathic lipids
Phosphoglycerides, Sphingolipids, Cholesterol, and Membrane Glycolipids
What are phosphoglycerides?
Derivatives of glycerol-3-phosphate with two fatty acyl chains esterified to a glycerol backbone and polar head attached to a phosphate group
What are the four head groups that can attach to the phosphate?
Phosphatidyl-ethanolamine (PE), phosphatidyl-serine (PS), phosphatidyl-choline (PC-most common) and sphingomyelin. (And inisitol- PI)
What is sphingomyelin?
It is a specialized membrane lipid
What is a sphingolipid?
Has a phosphate head where the lipid is derived from sphingosine
What is a common sphingolipid and where is it found?
Sphingomyelin; it makes up myelin sheaths around axons in the brain
What are lipid rafts?
Microdomains in membranes made of sphingolipids
What is the function of cholesterol?
It modulates membrane fluidity
What is cholesterol made of?
It is mostly hydrogen and carbon with a small polar OH
How are membrane glycolipids formed?
By adding carbohydrate (sugar) groups to the lipids- occurs in the golgi.
What determines blood type?
The sugar of the glycosphingolipid (either A or B) that is expressed on the surface of red blood cells
What are the functions of glycolipids?
Cell-cell adhesion, cell-cell recognition, and the alteration of electrical gradients (sugars are often charged and always polar)
What are the methods of movement of the phospholipids in the bilayer?
Lateral (side to side- rapid and frequent) and flip flop (switches sides of the bilayer- rare because polar head group does not cross hydrophobic core)
What does FRAP stand for?
Fluorescence recovery after photobleaching
What is FRAP used for?
To study membrane fluidity
What factors influence membrane fluidity?
Lipid composition, structure of phopholipid tails, and temperature
Which phospholipids are present in the extracellular leaflet?
PC and sphingomyelin
Which phospholipids are present in the intracellular leaflet?
PE and PS
How is membrane asymmetry accomplished?
Phospholipids are synthesized in the smooth ER and inserted into a bilayer at a lumenal face
How are phospholipids transferred to the cytoplasmic face?
Enzymes called flipases move them.
What are integral membrane proteins?
Amphipathic proteins that span the core of the membrane
What are peripheral membrane proteins?
Proteins that do not contact the hydrophobic core of the membrane but associate with integral or lipid- anchored proteins or have direct interactions with lipid head groups
What are lipid anchored membrane proteins?
Proteins bound covalently to one or more lipid molecules
What are outer leaflet proteins linked to?
Covalently linked to GPI (glycosylated inisitol)
What are inner leaflet proteins linked to?
The #5 protein is linked to a fatty acid tail or isoprene derivative
What is myristalation/palmilation?
The attachment of inner leaflet proteins to a fatty acid
Why do membrane proteins have asymmetric topology?
So that the membrane can have different functions on either side.
How do you freeze fracture a membrane?
The membrane is quickly frozen and sliced with a “diamond knife” so it splits down the hydrophobic middle
What is the purpose of freeze fracturing a membrane?
It allows us to view the membrane proteins
How does trypsin allow us to study membrane proteins?
It is a non-specific protease, so by digesting proteins under certain conditions, it can help us differentiate intra and extracellular membrane proteins
Describe the permeability of the bilayer to different types of molecules
Permeable to small, uncharged or hydrophobic molecules; relatively permeable to small uncharged polar molecules; mostly impermeable to large uncharged and polar molecules; and impermeable to charged molecules )(ions)
How do impermeable molecules cross the bilayer?
Simple diffusion, facilitated diffusion, and active transport
What do carrier proteins do?
They bind solutes on one side of the membrane, undergo a conformational change, and transfer solutes to the other side of the membrane
What do channel proteins do?
Form hydrophilic channels through the membrane to allow the passage of solutes without a change in the protein’s conformation
What are gated channels?
Channel proteins that open only under certain conditions
How do gated channels open?
The channel can undergo a depolarization event or a chemical-gated channel can rely on the binding of a particular substance
What are the three ways energy can be supplied for active carriers?
ATP hydrolysis, coupled transport, and light driven
Describe a Na/K pump
3 Na are pumped out and 2 K are pumped in against the concentration gradient for each ATP consumed
What is coupled active transport?
The movement of two molecules simultaneously, where one molecule moves using the energy gradient from the other molecule
What is the difference between symport and antiport?
Symport- molecules move together
Antiport- molecules move in opposite directions
