Chapter 7 - Membranes, Lipids, and Enzymes That Modify Them Flashcards
What is the main thing that separates the cytosol from the outside environment?
water-impermeable lipid membrane
____ dictates spontaneous organization into self sealing sheets and vesicles.
hydrophobicity
What are self sealing sheets and vesicles driven by?
high thermodynamic cost
Due to the lipid membrane’s ____ arrangement, the biochemical reactions in which they participate have different properties from the aqueous environment that allows free diffusion in ____ space.
2D; 3D
What kind of molecules is the lipid bilayer composed of?
amphipathic
What kind of structure is favored for relatively large polar heads and small hydrophobic tails?
micelles
When there is a tear in the lipid membrane, which portion becomes exposed to water?
hydrophobic portion
What factors does the fluidity of the membrane depend on?
1) phospholipid composition
2) nature of the hydrocarbon tails (saturation status)
3) amount of cholesterol (animal cells)
When a phospholipid has a shorter tail, what does it mean?
- less interactions between tails
- increase in fluidity
When there are more double bonds in a phospholipid tails, what happens?
kinks interfere with packing closely which increases fluidity
Some cells change the ____ of membrane lipids to adjust its fluidity as an adaptation measure.
composition
What is the most abundant lipid in biological membranes?
glycerol phospholipids
What kind of linkage exists in a glycerol phospholipid between the glycerol and the hydrocarbon tails?
ester linkage
What is the general length of a hydrocarbon tail?
14-20 carbons
What kind of phospholipid is this?
phosphatidylethanolamine
PE
What kind of phospholipid is this?
phosphatidylserine
PS
What kind of phospholipid is this?
phosphatidylcholine
PC
What kind of phospholipid is this?
phophatidylinositol
PI
What kind of phospholipid is this?
sphingomyelin
(sphingolipid)
** move picture here
This lipid is abundant in the plasma membrane of _________ cells.
animal cells
mammalian cells
How would you describe a sterol?
- rigid
- planar
- polycyclic compound
- relatively non-polar
What is the term which relates to cholesterol’s ability to manipulate the fluidity of the lipid bilayer?
“temperature buffer”
warm - lots of cholesterol stiffens
cold - protects cell membrane from being too rigid
How many rings does cholesterol consist of?
4 fused rings
What structure is this?
cholesterol
Which kind of lipid molecules are mainly located in the plasma membrane and have sugar groups as heads?
glycolipids
Where do glycolipid molecules acquire their sugar groups from?
Golgi lumen
Which kind of lipids give off an “apoptotic” signal in the bilayer?
phosphatidylserine
PS
Which kind of lipids are primarily found on the cytosolic leaflet?
phosphatidylinositides
PI
Which enzyme catalyzes the transfer of random phospholipids from one monlayer to another?
scramblase
in the ER
Which enzyme catalyzes the transfer of specific phospholipids to the cytosolic monolayer?
flippase
in the Golgi
What organization state of the lipid bilayer?
- loose & fluid
- high lateral mobility
- hydrocarbons tails
- cis-double bonds
liquid-disordered
unsaturated
Which organization state of the lipid bilayer?
- dense packing
- limited lateral mobility
- hydrocarbon
solid gel
saturated
Which organization state of the lipid bilayer?
- highly ordered
- realtively fluid
- hydrocarbon chains
- cholesterol enriched
liquid-ordered (raft)
saturated
enriched in spingolipids
What is directly realated to the behavior of proteins embedded, and lipids that act as signaling intermediates (e.g. DAG)?
fluidity and the rate of protein diffusion
What kind of reaction can make molecular interaction more efficient?
membrane association
Membrane associations show that two interacting protiens bind the most productively in what orientation?
in a certain, precise orientation
When two proteins are free in a solution, what is their behavior?
- both can rotate around all three axes
- only as small fraction of collisions will be properly oriented
When two proteins are confired to the membrane by an anchor, what is their behavior?
- allowed to rotate only around one axis
- increases the probablity of collision via proper orientation
Different ____ of the membrane have differnt compositions and physical properties.
domains
The diffusion rate by ____ and ____ shows that the membrane lipids and proteins in the real biological membranes diffuse significantly slower than in artificial membranes consisting of pure lipids.
SMT; FRAP
The diffusion rate by SMT and FRAP shows that the membrane lipids and proteins in the real biological membranes diffuse significantly ____ than in artificial membranes consisting of pure lipids.
slower
Why do membrane components move much slower between adjacent domains?
- high density of membrane proteins causing physical contraints
- cytoskeletal structures that may corral membrane proteins
- distinct membrane domains with different fluidity
When we say signaling proteins are less transient when they are associated with membranes, what does this mean?
they are more likely to run into each other
A technique to study movement of proteins (especially membrane proteins)
Fluorescence Recovery After Photobleaching
FRAP
What is FRAP?
Fluorescence Recovery After Photobleaching
What does FRAP determine?
How fast a photobleached blindspot is able to be repaired by protein recovery.
How can we track the movement of proteins?
in trajectory of motion (seconds)
What can reveal some of the pathways that real proteins follow on the surface of a living cell?
single molecule tracking (SMT microscopy)
Signaling membrane lipids involves their ____ or ____ modification in response to input stimuli.
breakdown; chemical
What do phospholipases do?
cleave/break down phospholipids
How are phospholipases classified?
by the position of the bonds the enzymes cleave
What does phospholipase A2 (PLA2) do?
cleaves the fatty acid chain from the middle position of the glycerol backbone
- lyso-phospholipid
- free fatty acid (archidonic acid)
both are bioactive and are the building block for eicosanoids
What does phospholipase C (PLC) do?
cleaves the phosphorylate head group from the phospholipid
- DAG
- head group moitey
What does phospholipase D (PLD) do?
cleaves the unphosphorylated head group
- phosphatidic acid (PA)
PA - acts as a bioactive molecule activating mTOR
What structure is this?
choline
purple: head group
pink: phosphate
What structure is this?
phosphocholine
purple: head group
pink: phosphate
What structure is this?
DAG
What structure is this?
fatty acid
purple: head group
pink: phosphate
What structure is this?
lyso-PC
pink: phosphate
purple: head group
Which cleavage site is represented by the pink arrow?
phosphatidylcholine
phospholipase D
- choline
- PA
Which cleavage site is represented by the green arrow?
phosphatidylcholine
phospholipase D
- phosphocholine
- DAG
Which cleavage site is represented by the blue arrow?
phosphatidylcholine
phospholipase A2
- lyso-PC
- fatty acid
What are the products of the cleavage of phosphatidylcholine via phospholipase A2 (PLA2)?
- lyso-phosphatidylcholine
- fatty acid (arachidonic acid)
What are the products of the cleavage of phosphatidylcholine via phospholipase C (PLC)?
- phosphocholine
- DAG
What are the products of the cleavage of phosphatidylcholine via phospholipase D (PLD)?
- choline
- phosphatidic acid (PA)
What structure is this?
sphingosine
What structure is this?
A Ceramide
What structure is this?
A Sphingomyelin
(phosphocholine head group)
What structure is this?
A Sphingomyelin
(phosphoethanolamine head group)
What structure is this?
A Cerebroside
What structure is this?
A Ganglioside
Which sphinolipid structure can have either a phosphocholine or a phosphoethanolamine head group?
A Sphingomyelin
PIP2 undergoes hydrolysis via ____ and produces what two components?
PLC (phospholipase C)
- DAG
- IP3
Which OH positions on this phosphatidylinositol (PI) are available for phosphorylation?
positions 2-6
What do kinases and phosphatases do to membrane lipids?
- phosphorylation and dephosphorylation
- change local concentration of various lipids isoforms
How are is the activity of kinases/phosphatases regulated?
- changes in the PTM
- sub-cellular localization
Commonly regulated in signaling to generate a variety of bioactive compounds.
phosphoinositides
What do DAG kinases do?
convert DAG to PA
What do sphingosine kinases do?
convert sphingosine to sphinogsine-I-phosphate (SIP)
can activate the GCPR
What are sphingolipids enriched in?
a myelin sheath
What does DAG and IP3 play a crutial role in?
- PKC activation
- ER calcium channels
