Chapter 11 - Lipids Flashcards
. Plant membranes have a higher percentage of unsaturated fatty acids than animal membranes.Animal membranes are ( less or more) fluid than plant membranes.
less fluid (more rigid)
Name an important representative of a steroid.
cholestrol
Where does most new membrane synthesis take place in a eukaryotic cell?
ER
In addition, the more closely packed the fatty acid tails, the ____ fluid the membrane; ________ fatty acid tails have no double bonds and can pack more closely together.
less; saturated
Membranes ____ their orientation during transfer between cell compartments.
retain
There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the **most highly mobile** phospholipid (listed as # of carbons and # of double bonds, respectively)? a) 24 carbons with 1 double bond; b) 15 carbons with 2 double bonds; c) 20 carbons with 2 double bonds; d) 16 carbons with no double bonds
b) 15 carbons with 2 double bonds;
In the Golgi and other cell membranes, phospholipid distribution is ____.
asymmetric
Which type of lipids are the most abundant in the plasma membrane?
phospholipids
The association of membrane proteins with lipids in the membrane bilayer always involves _____.
hydrophobic interactions
Lipid molecules in biological membranes are arranged as a continuous double layer called the ______________, which is about 5 nm thick.
lipid bilayer
- A cell membrane made up primarily of lipids with which characteristics would be the least fluid (i.e., most stiff)?
long, saturated fatty acid tails
Membranes are transported by a process of ______ and ______. Here, a vesicle is shown budding from the Golgi apparatus and fusing with the plasma membrane. Note that the orientations of both the membrane lipids and proteins are preserved during the process: the original cytosolic surface of the lipid bilayer (green) remains facing the cytosol, and the noncytosolic surface (red) continues to face away from the cytosol, toward the lumen of the Golgi or transport vesicle—or toward the extracellular compartment. Similarly, the glycoprotein shown here remains in the same orientation, with its attached sugar facing the noncytosolic side.
vesicle budding; fusing
Sugar containing lipids called _________________________ are found only in the outer half of the bilayer and their sugar groups are exposed at the cell surface.
glycolipids
Name a lipid that is a fused ring compound.
steroids
There are several ways that membrane proteins can associate with the cell membrane. Membrane proteins that extend through the lipid bilayer are called __________________ proteins and have __________________ regions that are exposed to the interior of the bilayer.
transmembrane; hydrophobic
Enzymes called ______ then randomly transfer phospholipid molecules from one monolayer to the other, allowing the membrane to grow as a bilayer.
scramblases
Which of the following membrane lipids does not contain a fatty acid tail?
cholesterol
Membrane lipids are capable of many different types of movement. Which does not occur spontaneously in biological membranes?
switching between lipid layers
The ____ the fatty acid tail, the more tendency for interaction between the tails, which _____ the fluidity of the membrane.
longer; reduces
When membranes leave the ER and are incorporated in the Golgi, they encounter enzymes called _____ , which selectively remove phosphatidylserine and phosphatidylethanolamine from the noncytosolic monolayer and flip them to the cytosolic side.
flippases
There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the *least organized* phospholipid (listed as # of carbons and # of double bonds, respectively)? a) 24 carbons with 1 double bond; b) 15 carbons with 2 double bonds; c) 20 carbons with 2 double bonds; d) 16 carbons with no double bonds
b) 15 carbons with 2 double bonds;
We can estimate the relative mobility of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area. What is this method called? What does the abbreviation stand for?
FRAP: Fluorescence recovery after photobleaching
We can estimate the relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area. What is this method called? What does the abbreviation stand for?
FRAP: Fluorescence recovery after photobleaching
Eukaryotic plasma membranes contain especially large amounts of ___________________, which enhances the mechanical stability of the lipid bilayer.
cholesterol
The cystolic face of a membrane is ____ during transport.
constant
- _____________ are compounds that are insoluble in water and but soluble in nonpolar organic solvents.
Lipids
The most useful agents for disrupting hydrophobic associations and destroying the bilayer are _____________, which are small amphipathic molecules that tend to form micelles in water.
detergents
Give 3 examples of lipids that have open-chain compounds with polar head groups and long nonpolar tails.
fatty acids & phospholipids
____ and ____ are enzymes that transfer phopholipids from one member face to another.
scramblase; flippases
There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the *most organized* phospholipid (listed as # of carbons and # of double bonds, respectively)? a) 24 carbons with 1 double bond; b) 16 carbons with no double bonds
b) 16 carbons with no double bonds
Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes?
switching between lipid layers
Other proteins are __________________ attached to lipid molecules that are inserted in the membrane. __________________ membrane proteins are linked to the membrane through noncovalent interactions with other membrane-bound proteins.
covalently; Peripheral
Most animal fats are solid at room temperature, while plant fats remain liquid at room temperature. Which is a feature of lipids in plant membranes that best explains this difference?
unsaturated hydrocarbons
On the other hand, membrane-associated proteins do not span the bilayer and instead associate with the membrane through an α helix that is __________________.
amphipathic
There are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the *least mobile* phospholipid (listed as # of carbons and # of double bonds, respectively)? a) 24 carbons with 1 double bond; b) 16 carbons with no double bonds
b) 16 carbons with no double bonds
Glycolipids are synthesized in the _____ of the Golgi apparatus and _______ across the bilayer.
lumen; cannot flip-flop
Cell membranes consist mainly of _____________ and __________, also contain ____________ that are linked to lipids and proteins.
lipid bilayer; proteins; fatty acids?
Membrane Fluidity is controlled by fatty acid composition and cholesterol content. The membranes of prokaryotes, which contain no appreciable amounts of steroids are the most fluid. (True or false?)
True
_____ has the most fluid membrane.
bacteria
What kind of lipid molecule is represented in this figure?
phospholipids
Classify the lipids into main 2 groups.
1- open-chain compounds with polar head groups and long nonpolar tails
2- Fused ring compounds
When amphipathic molecules are placed in an aqueous environment, they tend to aggregate so as to bury their hydrophobic ends and expose their hydrophilic ends to water, giving rise to two different kinds of structures, either spherical _______________or planar _______________, with the hydrophobic tails, sandwiched between the hydrophilic head groups.
micelles;
bilayers
Which type of lipids are the most abundant in the plasma membrane?
phospholipids
All the lipids found in membranes are said to be ______________ because they have one hydrophilic end and one hydrophobic end.
amphipathic
Please understand Common Features of Biological Membranes
- sheetlike lipid bilayer structures; thickness ~60 Å-100 Å
- consist mainly of lipids and proteins
- lipids are small molecules that have both hydrophilic and hydrophobic moieties; low solubility in water and high solubility in nonpolar solvent (iso-propanol, tetrahydrofuran)
- Specific proteins mediate distinctive functions of membranes
- Proteins and lipids are held together by non covalent interactions
- asymmetric
- fluid structures
- electrically polarized, such that the inside is negative, typically 60 mV; K+ and Na+ are not easy to pass
through; H2O, CO2 and O2 are relatively easy
Which of the following membrane lipids does not contain a fatty acid tail?
Cholesterol. It has a ring structure.
Unsaturated fatty acids usually have ____________ double bonds.
cis
Where are new phospholipids made?
ER
Cell membranes are fluid, and thus proteins can diffuse laterally within the lipid bilayer. However, sometimes the cell needs to localize proteins to a particular membrane domain. Name three mechanisms that a cell can use to restrict a protein to a particular place in the cell membrane.
- The protein can be attached to the cell cortex inside the cell.
- The protein can be attached to the extracellular matrix outside the cell.
- The protein can be attached to other proteins on the surface of a different cell.
- The protein can be restricted by a diffusion barrier, such as that set up by specialized junctional proteins at a tight junction.
Membrane lipids assemble into in a membrane using
Hydrophobic forces
- A phospholipid is inserted into the cytosolic side of the ER membrane. Which of the following could randomly reposition this phospholipid to the other (lumen) side of the ER membrane?
Scramblase
Glycolipids on the surface of cells are especially important as cell markers.
(True or false?)
True
Lipids are created on the ___ surface of the ___.
cystolic; ER
