Midterm 2 Flashcards
plasma membrane
the outer boundary of the cell separating the cellular content from the outside world
What holds the lipid bilayer together?
The van der whal interactions between the acyl tails of phospholipids
Functions of the plasma membrane
1)Compartmentalization
2)Scaffolding for biological activities
3)Selective permeable barrier
4)Allowing transport of solute
5)Responds to stimuli
6)Cell to cell communication
7)Energy transduction
Lipid Bilayer
the structural backbone and barrier to prevent random movements of materials into and out of the cell
What type of interaction holds lipids and proteins together in the bilayer
noncovalent bonds
Three lipid types found in mammalian membranes
1)Phosphoglycerides
2)Sphingolipids
3)Cholesterol
Phosphoglycerides
Contain 2 fatty acids, a glycerol, and phosphate group usually linked to a small polar group
Sphingolipids
Lipids derivatived from ceramide that can add groups to their terminal alcohol
Glycosphingolipid
Sphingolipid with an additional carbohydrate found exclusively on the exoplasmic face of the plasma membrane
cholesterol
A polar ampipathic molecule that stabilizes and adds fluidity to membranes composed of a polar head group, steroid ring and hydrocarbon tail
Why is lipid asymmetry between the different leaflets of the bi layer important?
1) Negatively charged cytosolic face can help proteins bind via its charge
2)Signalling can be done via movement of material from the inner layer to the outer layer
3)Glycolipids only are found on the extra cellular side acting as a ligand receptor
glycosylation
Post transcriptional modification which adds carbohydrates to protiens
Three sub classes of membrane proteins
1)Integral membrane proteins- fully integrated into the bilayer
2)Peripheral Membrane proteins- anchored to the outside of the bilayer
3)Lipid anchored proteins- Covaletly linked to the membrane by a membrane protein
Functions of Integral Membrane proteins
1)Transporters: moving ions and solutes across the membrane
2)Anchors: binding intra- or extra- cellular components to the membrane
3)Receptors: binding ligands to initiate signal transduction pathways
4)Electron Transporters: transfer electrons during photosynthesis and respiration
Structure of Integral Membrane proteins
Composed of Alpha Helices and Beta Barrels
Why would the cytosolic side of a integral membrane protein be positively charged?
To anchor to the negatively charged cytosolic side of the membrane
Hydropathy plot
measures the hydrophobicity of amino acids where hydrophobic = +ve, hydrophilic = -ve
Peripheral Membrane proteins
Protiens which do not interact with the core of the lipid bilayer and are anchored via non covalent bonding between the head groups, they are easily removed via changes in Ph or ionization strength
Three types of Lipid anchored membrane proteins
1)Fatty acid- anchored membrane proteins
2)Isoprenylated membrane proteins
3)GPI-anchored membrane proteins
Fatty acid-anchored membrane proteins
Synthesized within the cytosol Attached to a saturated fatty acid, usually myristic acid(14C) or palmitic acid(16C), that is embedded in the membrane
Isoprenylated membrane proteins
Attached to multiple isoprenyl groups(5C), usually farnesyl(15C) or geranygeranyl(20C) groups,then embedded in the membrane, Synthesized in the Cytosol
GPI-anchored membrane proteins
synthesized in the ER, post-translationally attached to the C-terminus and can be released from the membrane via cleavage by phospholipase C
Fluid Mosaic Model
Membranes consists of a mosaic of proteins/lipids in a fluidic state
Why is membrane fluidity important
Vesicle formation, fusion, secretion
Cell division
Muscle contraction
Cell migration
Signalling mechanisms