Membranes and Membrane Transport Flashcards
Membrane formation is driven and maintained by what?
the Hydrophobic effect
What is the Fluid mosiac model?
Phospholipid bilayer acts like a 2 dimensional, fluid-like sea, with proteins and other macromolecues floating like icebergs within it
At human body temperature, what is the role of cholesterol in the bilayer?
Cholesterol RESTRICTS movement of the phospholipids within the bilayer, reducing its fluidity and permeability to small molecules
Describe the structure of cholesterol
- Polar head group
- Rigid steroid ring structure
- nonpolar hydrocarbon tail
What are three factors that increase membrane fluidity?
- Short fatty acid chains
- High unsaturation (one or more cis-double bonds)
- High temperatures
What class of molecule is this and where is it usually found?
- Esterified cholesterol
- Found in: Hydrophobic core of lipoprotein (such as chylomicrons)
What class of molecule is this and where is it usually found?
- Glycerophospholipid (composed of 2 fatty acids, glycerol, phosphate, and head group)
- Found in: Cell membranes (polar head group is oriented to face aqueous environment)
What class of plasma membrane proteins are these?
Integral membrane proteins
- Wind in and out of bilayer one or more times
What type of plasma membrane proteins are these?
Lipid-anchored proteins
- Hydrophilic proteins which are associated with the plasma membrane via a covalently attached lipid molecule that tether the protein to the membrane
- Ex: Ras
What type of plasma membrane protein are C and D?
Peripheral membrane Proteins
- Attached to the membrane by electrostatic or hydrogen bonds that noncovalently link them to integral membrane proteins or to phospholipid head groups
Describe the Glycocalyx and its importance
- Carbohydrates covalently bind to lipids and proteins on extracellular surface of plasma membrane
- These sugar residues absorb water which cushions the plasma membrane
- Referred to as (Cell Coat)
- ABO blood groups are determined by specific carbohydrate sequences in the cell coat of RBC
Movement of molecules across a membrane bilayer depends on what characteristics?
- Size: small molecules move across more easily
- Charge: only uncharged molecules can cross unassisted
- Hydrophobicity: only hydrophobic molecules can cross without assistence
- Solute concentration: Favored from areas of high concentration to areas of low concentration
Facilitated Diffusion
- Transport of molecules down an energectically favorable concentration gradient (high to low)
- Does not require extra energy input (passive transport)
Define the Electrochemical gradient
- Refers to transport of charged molecules
- Transport is influenced by concentration gradient AND the electrostatic environment (net charge)
Membrane potential
- Difference in net charge across the membrane
- also known as Voltage Gradient
What is the voltage gradient of most plasma membranes?
- Inside of cell is more negative than the outside
- Favors the entry of positively charged molecules
Do channel porteins bind to solutes?
- NO!
- Channel proteins form hydrophilic tunnel through bilayer that allows certain solutes to diffuse down their concentration gradient (passive transport)
- Can be gated (opening and closing in response to binding of signaling molecules)
Acetylcholine gated ion channel: purpose
- Binding of acetylcholine to channel allows NA+ to flow into the cell along its concentration gradient
- Influx of NA+ causes depolarization which signals muscle cells to contract
Do carrier proteins bind to solutes?
- Yes! carrier proteins bind to solutes for transport
- Can be involved in active or passive transport
Whats the difference between Paracellular and Transcellular transport?
- Paracellular: Passive; Between adjacent cells through tight junction
- Transcellular: Active and passive; Through cells
GLUT2 carrier protein:
- Location
- What does it transport?
- Type of Transport
- Cell membrane between enterocyte and basal side of cell (Connective Tissue and Blood Supply)
- Transports glucose
- Passive transport: concentration of glucose in enterocyte is higher than that of extracellular space
Primary Active Transport
- One step process that directly involves ATP to transport a solute against its concentration gradient
What is the function of the NA+/K+ ATPase?
- Pumps out 3 molecules of Na+ for every 2 molecules of K+ it imports into the cell
- Leaves cell with a negative charge
- Increases the electrochemical gradient of Na+ (higher levels of Na+ outside of the cell)
If the Na+/K+ ATPase releases Na+ to the basal side of the cell, how does the apical side of the cell get a high concentration of Na+?
Na+ at the basal side leaks back through tight junction to the apical side resulting in high levels of extracellular Na+ at apical surface
