Chapter 7 - Membranes, Lipids, and Enzymes That Modify Them Flashcards by Madison Webb

Q

What is the main thing that separates the cytosol from the outside environment?

A

water-impermeable lipid membrane

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Q

____ dictates spontaneous organization into self sealing sheets and vesicles.

A

hydrophobicity

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Q

What are self sealing sheets and vesicles driven by?

A

high thermodynamic cost

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Q

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.

A

2D; 3D

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Q

What kind of molecules is the lipid bilayer composed of?

A

amphipathic

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Q

What kind of structure is favored for relatively large polar heads and small hydrophobic tails?

A

micelles

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Q

When there is a tear in the lipid membrane, which portion becomes exposed to water?

A

hydrophobic portion

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Q

What factors does the fluidity of the membrane depend on?

A

1) phospholipid composition
2) nature of the hydrocarbon tails (saturation status)
3) amount of cholesterol (animal cells)

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Q

When a phospholipid has a shorter tail, what does it mean?

A

less interactions between tails
increase in fluidity

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Q

When there are more double bonds in a phospholipid tails, what happens?

A

kinks interfere with packing closely which increases fluidity

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Q

Some cells change the ____ of membrane lipids to adjust its fluidity as an adaptation measure.

A

composition

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Q

What is the most abundant lipid in biological membranes?

A

glycerol phospholipids

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Q

What kind of linkage exists in a glycerol phospholipid between the glycerol and the hydrocarbon tails?

A

ester linkage

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Q

What is the general length of a hydrocarbon tail?

A

14-20 carbons

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Q

What kind of phospholipid is this?

A

phosphatidylethanolamine
PE

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Q

What kind of phospholipid is this?

A

phosphatidylserine
PS

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Q

What kind of phospholipid is this?

A

phosphatidylcholine
PC

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Q

What kind of phospholipid is this?

A

phophatidylinositol
PI

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Q

What kind of phospholipid is this?

A

sphingomyelin
(sphingolipid)

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Q

** move picture here

This lipid is abundant in the plasma membrane of _________ cells.

A

animal cells

mammalian cells

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Q

How would you describe a sterol?

A

rigid
planar
polycyclic compound
relatively non-polar

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Q

What is the term which relates to cholesterol’s ability to manipulate the fluidity of the lipid bilayer?

A

“temperature buffer”
warm - lots of cholesterol stiffens
cold - protects cell membrane from being too rigid

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Q

How many rings does cholesterol consist of?

A

4 fused rings

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Q

What structure is this?

A

cholesterol

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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