Lecture 6 - Lipids, Membranes And Signaling Flashcards
What is the basic structure of fatty acids?
Which are most common in people?
Carboxylic acid with long hydrocarbon side chains
Fatty acids with 16 or 18 carbons
How does the omega nomenclature system work for fatty acids?
Specifies placement of final double bond, identifies the position of the last double bond relative to the last carbon (the omega carbon)
Which configuration of double bonds is most common in biology?
Cis
How does saturation vs unsaturation affect lipid packing?
Saturated FAs are linear and pack tightly with their atoms along the length in van der Waals contact with neighboring molecules.
Unsaturated FAs have at least 1 double bond that are in cis conformation and reduce the packing van der Waals forces between FAs
How does unsaturation affect fluidity?
Increased degree of unsaturation increases fluidity of substance (hence unsaturated FAs are liquid at room temp with lower melting point compared to saturated FAs and it has to do with reduced non covalent interactions between individual FAs)
What effect does partial hydrogenation have on vegetable oils?
Converts cis double bonds to single bonds and trans double bonds, preserves shelf life and stability of product
What impact do trans double bonds have on health?
Increased risk of heart disease
Increased blood TAGs and LDL cholesterol
Increased inflammatory response
What is the impact of trans double bonds on lipid packing?
Increased packing ability, increased van der Waals forces between FAs, decreases fluidity
Describe the structure of TAGs
What is the function of TAGs
3 fatty acid chains linked to glycerol backbone with ester linkages
Energy storage (more effective than carbohydrates for energy storage because they are less oxidized (aka more reduced) and carbohydrates pull water with them for storage but TAGs do not)
Structure of glycerophospholipids
Glycerol backbone with 2 fatty acids and polar head made of phosphate group and alcohol group
These lipids are named after their polar heads
Describe the structure of sphingolipids
Sphingosine backbone with fatty acid attached via amide linkage to backbone, different polar heads attached to carbon 1
Sphingomyelin is the ___ _____ sphingolipid.
It is composed of a ____ with a ____ head group.
Most common
Ceramide, phosphocholine
Cerebrosides have a ___ with a ___ head group
Gangliosides have a ___ with a _____ head group
Ceramide, single carbohydrate
Ceramide, polysaccharide
What is a sterol?
What is the general structure?
Structural lipids present in membrane
3 six membered rings and 1 five membered ring all fused together
Cholesterol is a component of _____ and is a precursor to ___ and ___.
Membranes
Bile acids and steroids
Lipid bilayers are ___ for biological systems
They form ___ due to the ___ ___
A barrier
Spontaneously, hydrophobic effect
Is the thickness of the phospholipid bilayer constant?
No - depends on length of FA chains and how they interact with one another.
What does the melting point of a membrane (transition from crystalline state to fluid state) depend on?
Length of FA chains (longer = more van der Waals forces) and degree of saturation (more saturated = more solid)
How does cholesterol affect membrane fluidity?
Ring structure of cholesterol restricts movement of nearby FA chains and decreases fluidity
Insertion of cholesterol can prevent packing and increase fluidity
Dual action helps maintain membrane fluidity over broad range of temperatures
Is the lipid bilayer symmetric?
No - certain FAs are more common on one side than the other.
How can lipids move in the membrane?
Laterally (very fast and has low thermodynamic barrier)
Lipid can flip from outer layer to inner layer (has to be catalyzed by ATP and enzymes such as flippase (out to in) or floppase (in to out) or scramblase (moves in out or out in))
How do peripheral membrane proteins associate with membrane?
Through hydrogen bonds with polar head groups
What is a lipid raft?
A region of the membrane that is tightly packed with glycosphingolipids and cholesterol. They are thicker, more ordered and associate with specific proteins. The components of the raft move as a unit and are important for signaling.
Why are lipid rafts important to signaling?
They cluster membrane components of signaling cascades together and create a localized signaling unit which enhances interactions and makes signaling more efficient.
What is a distinguishing feature of carriers?
The molecule that they transport binds to them, causes a conformational change and then that change allows passage of the transporter molecule.
NOTE: a ligand binding to a membrane protein and changing the shape of the protein is NOT considered a carrier because the ligand is not being transported through the membrane.
Receptor
Protein in the membrane which binds a signaling molecule / ligand and transfers information from the environment to the cell’s interior
Second messenger
Small molecules that are generated intracellularly when a signaling molecule activates a receptor
What are the 4 main steps of signal transduction?
1) specificity
2) amplification
3) desensitization / adaptation
4) integration
Describe the process of G protein coupled receptors
1) Epinephrine binds to transmembrane region
2) GDP on G alpha subunit swapped for GTP
3) G alpha subunit moves to adenylate Cyclades and either stimulates it (Gs) or inhibits it (Gi)
4) Adenylate Cyclades affects cAMP production
5) cAMP activates Protein kinase A
6) PKA phosphorylates cellular proteins and causes signal transduction
How are signal cascades turned off?
1) intrinsic GTPase activity of G proteins
2) short half life of second messengers
3) reversal of phosphorylation by removal of phosphate group by phosphatase
4) desensitization of receptor to a signal
Single fatty acids form a ____ lipid barrier.
Phospholipids form a ___ lipid barrier
Triacylglycerols form a ___ lipid barrier
Micelle (triangular shape)
Bilayer (rectangular shape)
Liposome (bilayer that forms a circular shape, inside contains hydrophilic pocket)
How does the composition of the cell membrane change during apoptosis?
During apoptosis, scramblase flips phosphatidylserine (PS) from the inner to the outer leaflet. Under normal circumstances this is energetically unfavorable because the polar head group has to travel through the hydrophobic center of the bilayer for this to happen
