Lecture 13 Flashcards
T or F, lipids are structurally and functionally diverse group of molecules
True
Describe the amphipathic properties of membrane lipids.
- Apolar tail (hydrophobic)
- Polar head (hydrophilic)
- polar head associates with water and nonpolar tail hides from water
– don’t form large covalent polymers instead they ten to associate w/ each other through noncovalent interactions
– stabilized through the hydrophobic effect
– also stabilized through van Der Waals interactions between hydrocarbon regions of molecules
What are primary components of membranes?
lipids
What are key components of lipids?
– fatty acids –> long hydrocarbon chains (14-24 C) with carboxyl group
What is an oleate ion?
– an unsaturated fatty acid with one cis double bond
What is a stearate ion?
Stearate (the anionic deprotonated form of stearic acid) it is a saturated fatty acid
In most naturally occurring unsaturated fatty acids what is the orientation?
- Orientation is about double bonds is cis rather than trans
- this has an important effect on molecular structure bc each cis double bond inserts a bend into the hydrocarbon chain
What is the difference between saturated and unsaturated fatty acids
- unsaturated –> liquid at room temp
- Saturated –> solid
– usually an even number of carbons
Why is unsaturation important?
- because it keeps membranes fluid instead of solid
- - helps with movement and conformation changes of transmembrane proteins
What is the importance of straight fatty acid tails?
– they can pack together and interact
– increasing number of van der Waals contacts to form regular semi crystalline structures
What is the nomenclature of a double vs saturated fatty acid
double is enonated whereas saturated is anoate
What makes up a triaglycerol?
Fatty acids + glycerol
– a glycerol molecule, which is a 3 carbon with OH at each carbon and a three carboxylic acids esterified to the
– water-insoluble, so must have a specific mechanism of transport in the body
What are the effects of the amphipathic nature of membrane lipids?
They will preferentially arrange into micelles or bilayers to bury phobic tails away from the aqueous environment
– self assembly process driven by hydrophobic interactions between fatty acid cahins
– close packing is directed by van der Waals interactions between hydrocarbon chains
What is the most abundant lipid in membranes?
– Glycerophospholipids
What is the general structure of glycerophospholipids?
carbon one and to have an acyl group and carbon three has an orthophosphate group attached with a philic group attached
What is the general structure of a sphingolipid? What is this basic structure called?
it is a C15 on the C1, an amine on C2, and C3 containing a hydroxyl group. Called a sphingosine unit
What is the structure of glycosphingolipids? What category do these lipids fall under?
contains a C15 on C1, an amide on C2, and a sugar on C3. Categorized as glycolipids
What is the non-sugar portion of glycosphingolipids generally referred to as?
Ceramide
True or false. glycolipids can have many carb residues and are oriented asymmetrically in the plasma and are always facing the extracellular side.
True
True or false.
glycolipids can be components of RBC membranes
True
What is the general function of cholesterols in the membrane?
act as a fluidity buffer
What does cholesterol due at each extreme in temperature?
it cold temps it prevents close packing and increases fluidity whereas at high temps it prevents excessive movement and decreases movement.
What is the general structure and characteristic of cholesterol
tetracyclic molecule that has a weak ampihatic nature, polar groups, rigid ring system, and a flexible tail.
True or false. Brain cells commonly have cerebrosides and ganliosides
True
True or false
axons are rich in glycosphingolipids
True
What maintains glycolipids in the rigid aqueous face configuration?
the inability of these lipids to move from these positions maintained by the limited flip flip ability of proteins
What are the typical ratios of lipid:protein?
1:4 or 4:1
What type of proteins exist in RBC membrane, retinal rod cells, vs SAR muscle cells in terms of size?
larger exist in RBC + SAR and smaller size exist in Retinal rod cells
What differentiated anchored proteins from peripheral and integral proteins?
anchored protein are covalently linked to fatty acids chains or glycolipids at surface whereas the other types are associated by non-covalent interactions
True or false
Diffusion is mainly lateral and rapid and rarely transverse.
True
What factors of membranes increase fluidity?
short fatty acid tails, unsaturated fatty acids, and cholesterol
True or false.
Saturated fatty acids decrease the Tm of the membrane
false they increase by increasing number of hydrogen bonds
true or false
outer and inner membrane differ in lipid composition and in types of associated proteins
true
What enzyme is responsbile for flipping lipids between inner and outer membranes?
flippase
True or false
orientation of transmembrane proteins does not change over time
true
true or false.
outer plasma membrane is rich in cholesterol
false. it is rich in glycosylated protein and lipids
true or false
fats tend to be saturated in animals and unsaturated in plants
true
Integral proteins are held by noncovalent forces. True or false?
true
What are the characteristics of the glycophorin integral protein?
ampihphatic with extracelluar portion that is rich in phillic AA Ser Thr Asp and a phobic alpha helix in the membrane that has phobic amino acid.
It is also a glycoprotein meaning it has sugars attached to its structure
What are common characteristics of protein/membrane interactions in integral protein?
typically 7 alpha helices that span the membrane with 20aa/helix with extensive H bonding
there are the typical 3.6aa/turn and 1 turn=0.54nm
bilayer core is about 3nm
What characteristic does bacteriorhodopsin have?
has a light absorbing pigment at its center that captures light energy and pumps protons from cell to outside
– acts as a proton pump
If a phobic index is positive, does it mean it is phobic or phillic?
phobic. negative values are phillic.
What information can you get from a phobic index?
it can help you see which sections of the protein is in the membrane/ specific AA involved at teach section. The groups let you see how many helices the protein has in the membrane
What is the structure of a transmembrane porin?
it is made of an amphiphatic b barrel structure. Hydrophillic residues on the inside of the channel and phobic residues on the outside facing the lipid bilayer.
What is the general function of membranes?
transport of substance in and out of cell ion transport and nerve cell conductance cell signaling maintaining shape cell-cell interaction
