Unit 3: Chapter 12 Flashcards
Characteristics of Membrane
- sheetlike structures
- composed of lipids and proteins which can be decorated with carbohydrates
- membrane lipids are small amiphipathic molecules which prevent movement of polar or charged molecules
- proteins serve to mitigate impermeability of membranes
- noncovalent assemblies
- asymetric
- fluid structures
- electrically polarized
What form lipid bilayers in aqueous solutions?
phospholipids and glycolipids
Formation of membranes is powered by
Hydrophobic effect
Liposome/ Lipid Vesicles
Double layered formed by phospholipids
Amphipathic
Very small aqueous compartment enclosed by a lipid membrnae
Used as drug delivery systems
The phospholipid bilyaer membrane is stabilized by
energy gained from hydrophobic groups burying hydrophobic groups out of contact with water
1. hydrophobic chain in water forces the formation of a cage of water around it
2. several hydrophobic regions cluster in bilayer, surface area exposed to water decreases and water molecules in cage are released (increase in entropy to drive formation of water)
Micell
Single hydrophobic tail instead of double
Inside is more hydrophobic
Lipid bilayerd are highly imermeable to ions and most polar molecules due to
Hydrophobic tail is picky
Larger permeability coefficient represents
increasing permeability
(easy to cross membrane)
What are the best molecules to cross membrane?
Small, uncharged, nonpolar
Ex. H20, indole, uren, glycerol
What is membrane fluidity controled by?
Fatty acid composiiton and cholsterol content
Membrane temperature is dependent on
Length of fatty acids and degree of cis saturation
Increasing temperature causes what to membrane
Increases fluidity of membrane to make more fluid like
Decreasing temperature causes what to membrane
Decreases fluidity of membrane to make more solid like
Abrupt transition between fluid like and solid like of membrane depends on
length of fatty acid chains and degree of unsaturation
How does cholesterol determine membrane fludiity in animals?
Makes membrane from becoming too rigid and too fluid
helps resist change and acts like buffer
1. prevent solidying at temp below Tm (too rigid)
2. sterically blocks large amount of fatty acids at temperature above Tm (too fluid)
What decreases fluidity of membrane?
Increase fatty acid tail
More closely packed
Less double bonds (saturated)
Why are proteins second most common componet of membrane?
Proteins allow transport proteins of molecules and information across the membrane
Integral membrane proteins
Embedded across entire membrane
Peripheral membrane proteins
Bound to polar head groups of membrane lipids or exposed surfaces of integral membrane proteins
Common structure of integral proteins
membrnae spanning alpha helices and beta strands
Bacteriorhodopism
Integral protein
Made of 7 alpha helices
Bacterical porin
Found in mitochondria, chloroplast, and bacteria
Forms pore or channel to help ions pass
How do lipids and membrane proteins diffuse
Laterally (side to side) in same layer
Rapid
- But can also use transverse diffusion
Fluorescence recovery after photobleaching (FRAP)
Technique that allows measurement of lateral mobility of membrane componets
Transverse diffusion
AKA flip flop
Very slow
Lipids and membrane proteins move to one layer to the other
Requires protein and enzyme for help
Reason why membrnae composiiton is asymmetric
Flippase
Moves membrane lipids from outer leaflet to the inner leaflet during transverse diffusion
Major function of membrane proteins is to function as
Transporters
(Simple transport and active transport)
Small molecules will spontaneously occur if:
(simple diffusion)
- concentration of the molecule is higher on one side of the membrane than the other
- the molecule is lipophilic or soluble in nonpolar solutions
Simple diffusion
Passive transport
No proteins used to assist
Facilitated diffusion
Passive transport
Polar molecules diffuse across membrane down their concentration with assistance of channel proteins
Active transport
Movements of molecules against concentration from low to high that requires source of energy and proteins
2 classes of membrane transport:
Channels and Transporters
Channels
Used in passive transport
Selective
No conformation change
Transporters
Used in passive and active transport
Specifity
Conformational change with gates
Function as pumps and channels
Passive transport
Molecules move with concentration gradient from high to low concentration
No energy required
Na+ - K+ pump
Active transport using ATP hydrolysis
Simutaneously pump 3 Na+ ions out and 2 K+ ions in against concentration gradient
Both against electrochemical agents
Keep concentration gradient of Na+ outside
Na+ concentration gradient is energy source
Most animal cells contain concentrations of
High concentration of K+ and low concentration of Na+
What concentration is more outside cell?
Na+ concentration
What concentration is more inside cell?
K+ concentration
Secondary Transporters
( 2 things moving)
Use one concentration gradient to power formation of another
Symporters
Secondary transporters
Molecules move in same direction
Antiporters
Secondary transporters
Molecules move in opposite directions
How is gluocse moved into animal cells
Active transport against concentration gradient
Symporter powered by Na+ concentration as energy source and moves down concentration gradient
Ion channels
Passive transport systems
Activated by changes in voltage or by binding of specific molecules to the channels
Electrochemical gradient forces
- chemical gradient: concentration gradient
- electrical gradient: membrnae potential (voltage gradient)
