Lecture 6 Flashcards
Cytosol?
Area in the cell outside of the nucleus that does not include the organelles
Cytoplasm?
Cytosol + the organelles
What separates the cell from the external environment?
Plasma Membrane
Transmembrane Proteins?
-Regulate transport/signalling
-Synthesized in the ER, mature in the golgi and are transported via vesicles into the PM
-Proteins made in the cytosol do not integrate into the membrane
T/F: Components of the cytosol and nucleus are very similar?
Cytosolic proteins are very similar to nuclear proteins, all nuclear proteins are synthesized in the cytosol
T/F: ER, Golgi, Vesicles and Exterior of the cell are similar composition?
True, these components are never in contact with the cytosol and are separated by membrane bound vesicles. Lumen of the secretory organelles is continuous with each other and the extracellular space
Organelle not connected to the secretory pathway ?
Mitochondria
Cytosol vs Lumen ?
Cytosol: Reducing Environment
Lumenal: Oxidizing Environment (cysteines disulfide bonding)
Function of membranes ?
-Provide an enclosure to cells and organelles within cells
- Allow regulated transport + signalling
-Provide sites for chemical reactions (metabolism)
-Support contact with the environment outside of cells
Properties of membranes?
-Hydrophobic barriers between aqueous compartments
- Flexible
-Permeable to small hydrophobic molecules but not large/polar molecules
-Protein complexes control the movement across the membrane
-Can store energy as conc. gradients
Two components of membranes?
-Lipid molecules(phospholipids) + membrane proteins
Phospholipids?
-Form a bilayer
Polar head : in contact with aqueous environments (exterior or interior of the cell)
2 Hydrophobic tails: face each other in the interior of the membrane
Transmembrane Proteins?
-Transport molecules
-Can move laterally
- Cannot flip
Major lipids in the membrane?
-Phospholipids(all membranes)
-Cholesterol
-Glycolipids(only in PM)
Properties of all membrane lipids?
-Have polar heads and hydrophobic tails
T/F: Lipid composition of the membrane determines mobility, curvature and thickness of the membrane?
True
Describe the exact structure of the phospholipid?
-Amphipathic
-Polar head: choline(or other charged molecule), phosphate bound to glycerol
-Fatty acid tails: hydrocarbon tails,
How is the polar head group bound to the fatty acid tails?
Via an ester linkage between the glycerol and hydrocarbon tails
Saturated vs non-saturated fatty acid tails?
Saturated: No double bond
-Straighter/more flexible tails
Non-saturated: double bonds (kinks)
-reduce flexibility and length
Naming the phospholipid head group?
Depends on the charged molecule present
Ex. Phosphatidyl-choline, Phosphatidyl-serine (only negative head group), Phosphatidyl-ehtanolamine
What is phosphatidyl-inositol?
A phospholipid with a sugar instead of a charged molecule, hydroxyl group on the sugar can be phosphorylated
What is Sphingomyelin?
similar to the choline except the glycerol linkage is an amide linkage instead of an ester linkage
Glycolipids?
-Found on the outside surface of the PM
- Polar head groups contain different sugars (galactose, glucose or a NANA sugar)
-No phosphate
-Important for cell contacts
Cholesterol Structure?
-Steroid ring
- Polar head(hydroxyl group) contacts polar phospholipid heads
-Nonpolar hydrocarbon tails in contact with fatty acid chains
How does cholesterol impact the membrane?
When added to the membrane lateral mobility decreases which increases membrane rigidity
Fatty acids tails become longer and more rigid
Membrane Asymmetry?
-Lipid composition on each side of the membrane differs
- Plasma membrane: exterior has glycolipids, interior has negative charge (high phosphatidyl-serine conc.)
Which membrane has the highest level of cholesterol?
PM
Which membranes have the highest level of phosphatidyl-choline and phosphatidyl-ethanolmine?
-ER membrane and mitochondria
Lipid Rafts?
Regions of the membranes of the trans golgi and PM that are thicker and enriched with cholesterol. Microdomain
How does cholesterol make a membrane thicker?
Binds to phospholipids and straightens them.
How does the thickness of the membrane determine which proteins are transmembrane proteins?
If you have a very thick membrane, you will need a region of the protein that is larger(taller) to be inserted into that section
Where are phospholipids and cholesterol synthesized?
In the cytosolic side of the ER
How do we get phospholipids from the exterior of the membrane to the interior?
scrambalase enzyme in the ER flip phospholipids randomly until they create a balanced membrane with the same amount of phospholipids in the outside/inside
How is membrane asymmetry maintained?
Flippase enzymes recognize specific phospholipids and glycolipids and move them from one part of the PM to another
Flippase characteristics?
-ATP-dependent
-Lipid specific
-Directional
Which membrane has highest level of cholesterol?
PM
Which membrane contains glycolipids?
PM
Which membrane contains the highest level of sphinomygelin?
PM
Which membrane contains the highest level of phospho-choline?
Mitocondrial
What is a micro domain?
region of a membrane where a component is present in high concentrations
Example of a microdomain?
Lipid rafts
