1-22 Membranes and Microscopy Flashcards
5 Functions of biological membranes
- permeability layer
- compartmentalization of functions
- identification
- signaling
- energy storage
describe the permeability barrier function of biological membranes
controls what gets in and what gets out
describe the compartmentalization function biological of membra nes
allows functional compartmentalization
describe the identification function of biological membranes
proteins/lips/carbs that occur on surface of cell to identify different cells. (ex. A and b antigens of AB blood type)
describe the signaling function of membranes
receptors tell the inside of the cell what the conditions are on the outside
describe the energy storage function of biological membranes
any time you create a gradient across a membrane, can be used as a source of energy. Gradients are used to drive molecule transport, drive oxydative phosphorylation in mitochondria.
Common chemical features of membrane lipids
The membrane lipids are amphipathic molecules. Besides cholesterol, they have a three-carbon backbone with at least one fatty acid tail attached.
phospholipids
examples?
hydrophilic parts?
hydrophobic parts?
membrane lipid with phosphate.
includes phosphoglycerides (hydrophobic fatty acid chains, hydrophilic phosphorylated alcohol)
and sphingomyelin (hydrophobic fatty acid chains, hydrophilic phosphoryl choline)
glycolipids
example of?
describe.
hydrophobic parts? hydrophilic parts?
example of sphingolipid
sphingosine backbone with sugar (unlike phospholipids, not phosphate) attatched via ester bond.
hydrophobic parts - fatty acid chains, sphingosine hydrocarbon chain
sugar - hydrophilic
cholesterol
structure?
hydrophobic parts? hydrophilic?
build on a four ring steroid structure with a hydrophobic head group.
Ring structure and hydrocarbon are hydrophobic
the membrane proteins. do what?
- allow selective permeability
- carry out most of the specialized and specific cell functions of the membranes
- diffuse laterally (unless constrained) but don’t flip flop
most membranes have more ____ than _____
protein, lipid
peripheral membrane proteins
bound to membrane surface or to an integral protein.
released without disrupting bilayer
amphipathic molecules - hydrophobic regions interact with inner lipid part of membrane. hydrophobic regions interact with the head groups and aqueous environment.
integral membrane proteins
penetrate the lipid bilayer
require detergents to be released (must disrupt bilayer)
have a defined topography (orientation) that will not change since it was inserted into the membrane
how do lipids effect the physical characteristics of membranes?
interactions? kinks? cholesterol content? temperature? transport?
hydrophobic interactions by tails dictate the shape.
kinks in fatty acid chains decrease interactions/packing and increase fluidity
cholesterol incorporation causes a net decrease in membrane fluidity
higher temperatures causes lipids to pack loosely
membrane allows for passive trasnport of small, nonpolar substances. Larger substances cannot pass through the tight packing of fatty acid tails and polar substances cannot pass through the hydrophobic tail region
How do proteins effect the physcial characteristics of membranes?
Allow the membrane to be selectively permeable by carrying out facilitated diffusion. In general, proteins give specialized membranes their specialized characteristics
what are the sources of variation between biological membranes?
all membranes made of same basic molecules
relative composition and kinds of proteins present allow for differences
membranes with different degrees of unsat, various amounts of cholesterol, different types of membrane proteins will have different physical and biochemical properties.
The two halves of the bilayer must be
assymetrical
lipid rafts
purpose?
1) Higher content of sphingo lipisd - glycolipids, sphingomyelin
2) Longer fatty acid chains
3) Lots of cholesterol
4) Packed tightly, move as raft
purpose - gathering areas for subsets of protein
common chemical features of membrane lipids
amphipathic molecules.
Besides cholesterol, they have a three-carbon backbone with at least one fatty acid tail attached.
phosphoglyceride
fatty acid chain (hydrophobic) phosphorylated choline (hydrophilic)
sphingomyelin
fatty acid chain & hydrocarbon chain of sphingosine (phobic)
phosphoryl choline (philic)
glycolipid
fatty acid cahin and hydrocarbon chain of sphingosine
one or more sugars (philic)
cholesterol
hydrophobic part (entire molecule but OH group)
philic part - the OH group.
draw general structure of phosphoglycerides, sphingomyelin, and glycolipid
page 274
formation of lipid bilayers in aqueous solution is a
spontaneous process
driven by hydrophobic effect, van der waals forces, and electrostatic/h-bond interactions between polar head groups and water
lipid bilayers are ______
describe the compositions
outer half - phosphatidylcholine, sphingomyelin, glycolipids
inner half - phosphatidylserine and ethanolamine
cholesterol distributed evenly between 2 halves
lipid bilayers are permable to
small uncharged polar molecules
hydrophobic molecules
lipid bilayers are not permeable to
large uncharged polar molecules
ions
scramblases
move random phospholipids from one half of bilayer to another, redistributing phospholipids evenly between the two halves of the lipid bilayer
flippases
located on golgi and PM, move specific phospholipids from one side to another to create asymmetry
in aqueous solution at pH 7, a lipid bilayer will be most permeable to which of the following molecules:
Na+ ion, Cl- ions, water, glucose, valine
water
what determines if Na+ ions can cross a biological membrane?
the presence of INTERGRAL membrane proteins about to act as Na+ transporters.
Summarize the factors affecting membrane fluidity (temp, concentration of unsaturated lipids, length of fatty acid chains, cholesterol content)
Increasing fluidity: Higher temp more unsaturated lipids Shorter fatty acid chains lower cholesterol content
Which types of proteins are bound to surface of membrane and can be release without disrupting lipid bilayer
Peripheral membrane proteins
Which types of proteins penetrate lipid bilayer and require detergents to release them from membrane bilayer. They transverse the entire lipid bilayer
Integral membrane proteins
Where are membrane lipids synthesized?
ER
How to newly synthesized lipids insert themselves into bilayer?
Newly synthesized phospholipids insert themselves exclusively into the cytosolic half of the bilayer
What is a difference between the function of scramblase and flippase?
Scramblase flips lipids in the membrane to prevent asymmetry while flippase creates asymmetry that is needed for certain functions
Which of the following forces is LEAST important in driving formation of a lipid bilayer in aqueous solution?
A. The hydrophobic effect (removal of the hydrophobic lipid tails from water)
B. van der Waals interactions between the hydrophobic tails of the lipids
C. Electrostatic interactions between phosphate groups in the polar head groups of neighboring lipid molecules
D.Hydrogen bonding interactions between the polar head groups of the lipids and surrounding water molecules
Electrostatic interactions (repulsion) between the phosphates can actually oppose bilayer formation; all of the other forces help drive formation.
In aqueous solution at pH 7, a lipid bilayer will be MOST permeable to which of the following molecules:
A. Na+ ions
B. Cl- ions
C. water
D. glucose
E. valine as a free amino acid
Water
