Membrane Flashcards
What do membranes do?
Receive info, import and export small molecules, and have the capacity for movement and expansion.
What is the membrane structure?
Lipid bilayer with lipids and proteins interacting noncovalently.
What are the different types of membrane lipids and what characteristic do they share?
Glycolipid, cholesterol, phospholipid, all are amphiphilic.
Describe cholesterol and its role
reduces membrane permeability to small molecules. Role in fluidity is temperature dependent .
How do monolayers in plasma membrane move?
Monolayers (leaflets) commonly diffuse laterally but transverse movement (flip flop) is rare.
How is saturation related to fluidity?
Unsaturated hydrocarbon chains reduce membrane thickness and Shorter hydrocarbon chains makes membrane more fluid due to fewer interactions.
How did experiment between mouse and human cells show diffusion of proteins in membrane?
When they were mixed, the labeled proteins mixed and moved around.
Describe FRAP
Used to measure the rate of diffusion of lipids and proteins in the membrane
Higher rate of diffusion means a quicker rate of fluorescence return
How is mobility of proteins restricted in cell?
• Protein aggregation •
Tethering to a protein inside the cell •
Tethering to a protein outside the cell •
Cell-cell interactions •
Tight junctions •
Cytoskeletal Network
Where does phospholipid synthase occur?
In the ER
What do scramblases do?
They randomly distribute phospholipids in either direction toward equilibrium.
What do flippases and floppases do?
Move phospholipids from outer to cytosolic leaflet or vice versa, requires ATP unlike scramblase
What do membrane proteins do and what are their types.
They perform the tasks of the membrane. Integral and Peripheral Membrane Proteins.
Describe single vs multipass transmembrane alpha helices.
Single pass are mostly nonpolar with no proline. Multipass may have a mix of hydrophobic and hydrophilic, or be entirely hydrophobic depending on structure.
How many amino acids needed to span membrane as a helix?
20-30
Describe beta barrels.
H bonding between B strands, can’t be identified by hydropathy plot since only 10 amino acids required for B strand to cross membrane.
Where are oligosaccharides added in membrane?
Non cytosolic side of lipids and proteins.
Describe permeability of the lipid bilayer.
Small hydrophobic molecules like CO2 easily diffuse. Small uncharged polar molecules like H2O diffuse but with more difficulty. Large uncharged polar molecules like glucose hard to diffuse. Ions can not diffuse.
Describe diffusion and the difference between passive and active transport.
Diffusion is the movement down a gradient.
Passive uses a channel or transporter but no energy needed.
Active transport requires energy.
What are channel proteins?
Water filled pores through which solutes can diffuse.
How do transporters work?
They alternate between two conformations to mediate transport.
What are the types of transporters?
Uniport (One transported molecule), Symport (two molecules together), Antiport(one molecule on each opposite side.)
What is glut1-glucose transporter?
A passive transport uniporter that transports glucose to the cytosol.
What is the chloride bicarbonate exchanger?
A passive transport antiporter that uses Cl- and other molecules to cause exhalation and movement of CO2.
What are the steps of the CBE?
- CO2 reacts with H2O, through carbonic anhydrase to from HCO3- and H+
- HCO3- moved out, Cl- moved in
- HCO3- moves into erythrocyte, Cl- out, CO2, and H2O formed
- CO2 leaves erythrocyte and is exhaled.
What are the different types of active transporters?
Coupled transporters that move multiple molecules across membrane and ATP driven pumps.
What does the Ca2+ pump do?
Functions in muscle cells to sequester Ca2+ in the Sarcoplasmic Reticulum, so it can be released during muscle contraction, Uses ATP as energy source.
What is the Na+/K+ pump?
An antiporter that uses ATP as an energy source and maintains concentration gradient and contributes to difference in charge across membrane.
How does Na+ /K+ pumping work?
Phosphorylation causes pump to hydrolyze ATP, triggering a conformational change that ejects Na+ and causes K+ to move in.
The pump then dephosphorylates itself, causing it to return to its original conformation and K+ is ejected.
What is the Na+/ Glucose transporter?
A symporter and gradient driven pump that uses the Na+ electrochemical gradient as an energy source for the pump, both molecules move in same direction.
What occurs in transcellular transport?
Intestinal cells transport glucose from the gut to extracellular fluid first, using sodium gradient to transport it against concentration gradient.
Then passive transport moves it from high to low concentration. Na+ moves out of cell through Na+/K+ pump.
What are the characteristics of ion channels?
They exist in open/closed states, can be regulated by gating and/or phosphorylation.
What types of ion channels are there?
Voltage gated, ligand gated (extracellular/intracellular ligand), mechanically gated.
How does the bacterial/k+ channel work?
Amino acids affect what goes through pore, number of interactions ion makes based on pore size and charge of amino acids surrounding the pore.
