Chapter 11 - Lipids

Question 1

. Plant membranes have a higher percentage of unsaturated fatty acids than animal membranes.Animal membranes are ( less or more) fluid than plant membranes.

Answer 1

less fluid (more rigid)

Question 2

Name an important representative of a steroid.

Answer 2

cholestrol

Question 3

Where does most new membrane synthesis take place in a eukaryotic cell?

Answer 3

ER

Question 4

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.

Answer 4

less; saturated

Question 5

Membranes ____ their orientation during transfer between cell compartments.

Answer 5

retain

Question 6

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

Answer 6

b) 15 carbons with 2 double bonds;

Question 7

In the Golgi and other cell membranes, phospholipid distribution is ____.

Answer 7

asymmetric

Question 8

Which type of lipids are the most abundant in the plasma membrane?

Answer 8

phospholipids

Question 9

The association of membrane proteins with lipids in the membrane bilayer always involves _____.

Answer 9

hydrophobic interactions

Question 10

Lipid molecules in biological membranes are arranged as a continuous double layer called the ______________, which is about 5 nm thick.

Answer 10

lipid bilayer

Question 11

3. A cell membrane made up primarily of lipids with which characteristics would be the least fluid (i.e., most stiff)?

Answer 11

long, saturated fatty acid tails

Question 12

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.

Answer 12

vesicle budding; fusing

Question 13

Sugar containing lipids called _________________________ are found only in the outer half of the bilayer and their sugar groups are exposed at the cell surface.

Answer 13

glycolipids

Question 14

Name a lipid that is a fused ring compound.

Answer 14

steroids

Question 15

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.

Answer 15

transmembrane; hydrophobic

Question 16

Enzymes called ______ then randomly transfer phospholipid molecules from one monolayer to the other, allowing the membrane to grow as a bilayer.

Answer 16

scramblases

Question 17

Which of the following membrane lipids does not contain a fatty acid tail?

Answer 17

cholesterol

Question 18

Membrane lipids are capable of many different types of movement. Which does not occur spontaneously in biological membranes?

Answer 18

switching between lipid layers

Question 19

The ____ the fatty acid tail, the more tendency for interaction between the tails, which _____ the fluidity of the membrane.

Answer 19

longer; reduces

Question 20

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.

Answer 20

flippases

Question 21

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

Answer 21

b) 15 carbons with 2 double bonds;

Question 22

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?

Answer 22

FRAP: Fluorescence recovery after photobleaching

Question 23

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?

Answer 23

FRAP: Fluorescence recovery after photobleaching

Question 24

Eukaryotic plasma membranes contain especially large amounts of ___________________, which enhances the mechanical stability of the lipid bilayer.

Answer 24

cholesterol

Question 25

The cystolic face of a membrane is ____ during transport.

Answer 25

constant

Question 26

1. _____________ are compounds that are insoluble in water and but soluble in nonpolar organic solvents.

Answer 26

Lipids

Question 27

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.

Answer 27

detergents

Question 28

Give 3 examples of lipids that have open-chain compounds with polar head groups and long nonpolar tails.

Answer 28

fatty acids & phospholipids

Question 29

____ and ____ are enzymes that transfer phopholipids from one member face to another.

Answer 29

scramblase; flippases

Question 30

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

Answer 30

b) 16 carbons with no double bonds

Question 31

Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes?

Answer 31

switching between lipid layers

Question 32

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.

Answer 32

covalently; Peripheral

Question 33

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?

Answer 33

unsaturated hydrocarbons

Question 34

On the other hand, membrane-associated proteins do not span the bilayer and instead associate with the membrane through an α helix that is __________________.

Answer 34

amphipathic

Question 35

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

Answer 35

b) 16 carbons with no double bonds

Question 36

Glycolipids are synthesized in the _____ of the Golgi apparatus and _______ across the bilayer.

Answer 36

lumen; cannot flip-flop

Question 37

Cell membranes consist mainly of _____________ and __________, also contain ____________ that are linked to lipids and proteins.

Answer 37

lipid bilayer; proteins; fatty acids?

Question 38

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?)

Answer 38

True

Question 39

_____ has the most fluid membrane.

Answer 39

bacteria

Question 40

What kind of lipid molecule is represented in this figure?

Answer 40

phospholipids

Question 41

Classify the lipids into main 2 groups.

Answer 41

1- open-chain compounds with polar head groups and long nonpolar tails

2- Fused ring compounds

Question 42

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.

Answer 42

micelles;

bilayers

Question 43

Which type of lipids are the most abundant in the plasma membrane?

Answer 43

phospholipids

Question 44

All the lipids found in membranes are said to be ______________ because they have one hydrophilic end and one hydrophobic end.

Answer 44

amphipathic

Question 45

Please understand Common Features of Biological Membranes

Answer 45

1. sheetlike lipid bilayer structures; thickness ~60 Å-100 Å
2. consist mainly of lipids and proteins
3. lipids are small molecules that have both hydrophilic and hydrophobic moieties; low solubility in water and high solubility in nonpolar solvent (iso-propanol, tetrahydrofuran)
4. Specific proteins mediate distinctive functions of membranes
5. Proteins and lipids are held together by non covalent interactions
6. asymmetric
7. fluid structures
8. 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

Question 46

Which of the following membrane lipids does not contain a fatty acid tail?

Answer 46

Cholesterol. It has a ring structure.

Question 47

Unsaturated fatty acids usually have ____________ double bonds.

Answer 47

cis

Question 48

Where are new phospholipids made?

Answer 48

ER

Question 49

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.

Answer 49

1. The protein can be attached to the cell cortex inside the cell.
2. The protein can be attached to the extracellular matrix outside the cell.
3. The protein can be attached to other proteins on the surface of a different cell.
4. The protein can be restricted by a diffusion barrier, such as that set up by specialized junctional proteins at a tight junction.

Question 50

Membrane lipids assemble into in a membrane using

Answer 50

Hydrophobic forces

Question 51

1. 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?

Answer 51

Scramblase

Question 52

Glycolipids on the surface of cells are especially important as cell markers.

(True or false?)

Answer 52

True

Question 53

Lipids are created on the ___ surface of the ___.

Answer 53

cystolic; ER