7. Cell Membranes Flashcards
What is the function of the smooth ER (3 points)
- Synthesis of lipids
- detoxification of drugs and poisions
- sotres ca2+ ions
What are two functions of the rough ER
- secretory proteins produced by ribsomes on outer surface
- membrane synthesis
What is the form and function of the plasma membrane
Its form is from a phospholipid bilayer (hydrophobic tails, hydrophilic heads) which functions as a seperation of intracelluar and extra celluar compartments
What type of lipid are the phospholipid bilayer tails made of? What is important about the structure of it?
Made of unsaturated fatty acids which has a kink in the tail
What are the three different types of lipids found in the plasma membrane?
Phospholipids - main strucutre
glycoproteins- only found in the outer membrane surface
cholestrol - 20% of all membrane lipids
What is the motion of the bilayer and what temperatures make the bilayer more fluid vs viscous
The phospholipids swap places by lateral movement and rarely by flip flop movement
at lower temperatures - membranes solidify
What is the symmetry like in the bilayer (form) and what are the functional compositions that result from this?
The bilayer is asymmetrical because there is rarely flip flow, therefore the bilayer of one side (inner leaflet) - faces cytosol, has a different composition to the bilayer on the other side (outer leaflet) - faces extra celluar space.
the functional consequences is
- Protein kinases C binds to phosphtidylserine (PS) in the inner leaflet only
- if PS moves to outer leaflet it signals a dying cell
What are three functions of a cell membrane
- is a physical boundry that seperates intracelluar and extracelluar matter
- has selective permeability to allow crossing of some substances
- the membrane proteins can determine the function of the cell
What are three things membrane proteins do?
- transport across the membrane
- signal transduction - receptors have binding sites that fit a chemial messenger eg a hormone
- form cell junctions
What is the cytoskeleton?
A dynamic, elaborate network of birds running through the cytosol, acting as the skeleton of the cell.
it anchors organelles and enymes
regualtes celluar activities (eg cell division)
What are the three types of cytoskeleton fibres and what type of protein are they made from?
Microtubules - tubulin
microfillaments - actin
intermediate filaments - keratin
What are three functions of a microtubules and what protein is it made of?
maintains cell shape
cell division
Motility (muscle contraction)
made of tubulin
What are mirofillaments made of what are three functions of it
Made of actin
maintains cell shape and involved in cell shape changes
movement (motility and muscle contraction)
cell division
What are intermediate filaments made of and name two functions
Made of keratin
maintains cell sape
anchorage of nucleus and some organelles
What is the flagella? What is the cilia? Name one difference in the movement
Flagella: a snakelike/whip that moves the cell forward
cilia: a back and forth motion that moves the cell sideways
flagella moves cell forward (think of a sperm cell) the cilia moves the cell sideways
In a cilia and flagella, name what the following structures are:
a doublet
dyenin arms
Doublet: there are 9 of these around in a ring on the outside made of microtubules.
dynein arms: attached to the doublet. Makes cilia and flagella ‘walk’ by ATP. The doublet grips the adjacent doublet, pushes it up, releases, then pushes again.
Why do cilia and flagellum bend?
When two adjacent doublets slide, they are physically restrained. Therefore they bend instead
What are motor proteins? (Where do they attache and what is their function?)
Attach to receptors on organelles to ‘walk’ the organelle along microtubules or microfilaments
How does the selective permeability and transport across membranes work?
Some molecules are restricted and other not. Depends on their composition
- charged molecules cant pass
- large molecules cant pass
- lipid solvable pass by dissolving in lipid bilayer
What is passive transport and what are the two types?
Passive transport is the movement of molecules down a concentration gradient (molecules trying to be even everywhere, eg osmosis)
two types are:
simple diffusion- hydrophobic, small, uncharge molecules moving down a concentration gradient by diffusing through the lipid bilayer
faciliated diffusion- hydrophilic substances diffuse through membranes down a concentration gradient. Using transport proteins (channels or carrier)
How do channel proteins and carrier proteins work in facilitated diffusion?
Channel proteins - a channel where solutes can pass (eg sodium channel)
carrier proteins - alternations between two conformations (open and closed) swallows solute on one side and spits it out on another
these proteins are located on the plasma membrane bilayer
What is active transport and give an example of how the process works
Active transport is working against the concentration gradient. Requires ATP for energy to move the molecules in and out of the cell.
Three sodium molecules and ATP bind to the protein receptor.
Sodium binding stimulates phosphorylation by ATP. ATP hydrolysis is required fro transport against the concentation gradient (basically ATP looses one phosphate and the protein changes shape to spit the sodium molecules to the outside of the cell)
extracelluar potassium binds to the proteins which releases the phosphate group
loss of phosphate restores the proteins original conformation.
Review image for details
