topic 4 - membranes Flashcards
what are lipids
water insoluble (hydrophobic) molecules composed mostly of C and H atoms (hydrocarbons)
what are biological lipids
triglycerides - energy storage
phospholipids and sterols - components of cell membranes
what are fatty acids
building blocks of triglycerides and phospholipids
hydrocarbons with a carboxyl group at one end (C double bond to O plus OH)
how do fatty acids vary
- number of carbons in the hydrocarbon (chain length)
- presence and number of C-C double bonds
what is the difference between unsaturated and saturated fatty acids
saturated - no C-C double bonds (saturated with H)
unsaturated - has 1+ C-C double bonds
what are triglycerides
energy storage molecules
3 fatty acids tails bound to a glycerol anchor
- glycerol forms an ester linkage to the fatty acid
what are the parts of phospholipids
polar/hydrophilic head group
- organic molecule (any alcohol)
- phosphate
- glycerol
non polar/hydrophobic tails
- 2 fatty acid tails (one saturated and one unsaturated)
what type of molecule is a phospholipid
amphipathic
how do phospholipids form bilayers in water
hydrophilic heads face the water - form H bonds and electrostatic interactions with each other and H bonds with water
hydrophobic tails hide from water on the inside of membrane - interact with each other through van der waals interactions
what is the function of biological membranes
compartmentalise the cell
- plasma membrane separates in from out
- internal membranes create additional cellular regions
- membranes are selectively permeable and scaffolds for communication and chemical reactions
what is the fluid mosaic model
lipids and proteins coexist in the membrane
carb groups can be attached to proteins or lipids
what is the difference between integral and peripheral proteins
integral = cross the bilayer (seen on both sides)
peripheral = interacting with either head groups or small part reach in
what factors increase the fluidity of the membrane
- increase temp
- unsaturated fatty acids (cis double bonds) - fatty acid tails dont pack as tightly together (fewer van der waals interactions)
- shorter chain length of the fatty acid (fewer C) - there are fewer atoms available to form van der waals interactions
what regulates membrane fluidity
sterols (ex: cholesterols)
how do sterols regulate membrane fluidity from the bilayer
prevent excess viscosity by stopping hte phospholipids from packing too tightly together
prevent excess fluidity by filling in gaps between phospholipids
what are sterols made of
amphipathic
- hydrophobic end
- fused rings (steroid nucleus) in hydrophobic hydrocarbon chain
- hydrophilic tail
what is the order of molecules that can pass through selective permeable membrane
- non polar (N2/CO2/O2) (quick diffusion, small (can slip through gaps), non polar = easy to move through hydrophobic centre)
- small uncharged polar molecules (water, glycerol) (slow diffusion across the membrane)
- large uncharged molecule (glucose/sucrose) (not able to diffuse - hydrophobic centre doesn’t want to let them through)
- ions (can’t diffuse - surrounded by water wolecules which make them too big to cross)
how does water cross membranes
aquaporins (water pores) - allow only water to pass through the membrane
- integral membrane protein
- hydrophilic interior (R groups) and hydrophobic exterior (interacts with the hydrocarbon chains of the phospholipids in the membrane)
what is the relationship between concen gradient and potential energy
large concen gradient = high PE
equilbrium = low energy state
what is tonicity
relative solute concen difference across a lipid bilayer
differences affect diffusion/osmosis across membranes
what are the differences between hypotonic, hypertonic, isotonic
hypotonic (lower concen outside) - water diffuses INTO the cell (cell swells)
hypertonic (higher concen outside) - water diffuses OUT of the cell (cell shrinks)
isotonic - same concen - no net mvmt
what are the two types of passive transport
simple diffusion
facilitated diffusion
what is simple diffusion
small hydrophobic and small polar solutes only
direction of mvmt = with concen gradient (powered by PE)
larger concen gradient = faster diffusion
what is facilitated diffusion
proteins shaped like tunnels cross the membrane and facilitate or allow the diffusion of large polar molecules or ions down/with their concen gradient
- tend to be substrate specific
- don’t require cellular energy
- rate depends on the concen gradient
- direction of the transport is reversible
what are the types of proteins involved in facilitated transport
channel proteins (tunnel)
- substrate specific
- allow mvmt along concen gradient (direction can change based on concen)
carrier proteins
- carry larger molecules (glucose/sucrose)
what is the difference between simple diffusion and facilitated diffusion relation between concen difference and rate of transport
simple diffusion = linear relationship
facilitated = non linear (sharp increase and plateau as it approaches max rate when all transporters are occupied)
what is primary active transport
highly specific protein pumps that cross the membrane
move the solute up or against its concen gradient (from low to high)
transporter uses ATP
often used by the cell to generate chemical and electrochemical gradients
what is secondary active transport
powered by energy released as a different solute moves
highly specific protein pumps that move solute up / against the concen gradient
what is the difference between symporters and antiporters
symporters
- both solutes move in the same physical direction
antiporters
- solutes move in opposite physical directions
