Week 7: Lipids, Membrane Structure, Energy of Membrane Transport

Question 1

The main energetic driving force for the formation of phospholipid bilayers is the _______ among the hydrocarbon tails of the phospholipids.

Answer 1

hydrophobic interactions

Question 2

The whole bilayer arrangement is held together by noncovalent interactions, such as ______ and _______.

Answer 2

van der Waals
hydrophobic interactions

Question 3

You have just isolated a pure lipid that contains sphingosine, a fatty acid, and a sugar moiety. To which class of lipids does it belong?

Answer 3

Glycolipid

Question 4

A glycolipid is a lipid to which a _______ is bonded. Quite frequently, ceramides are the parent compounds for glycolipids, and the glycosidic bond is formed between the primary alcohol group of the ceramide and a sugar residue.

Answer 4

sugar moiety

Question 5

Which of the following lipids is/are not found in animal membranes?

Answer 5

Triacylglycerols

Question 6

Triaclyglycerols are typically used for the storage of _____; they do not appear in cell membranes of ______. They are mostly deposited in ______ and are also found in the ______ in the form of very low density lipoprotein (VLDL) and chylomicrons.

Answer 6

fatty acids
animals
adipose tissue
blood

Question 7

_______ of the proteins associated with membranes span the bilayer from one side to the other.

Answer 7

Some

Membrane proteins can fully traverse the bilayer, they can penetrate a portion of the bilayer without crossing it, or they can be peripherally associated with the surface of the bilayer. The association of a particular protein with the membrane depends on the details of the protein’s structure.

Question 8

The rate of transport of a species through a protein channel does not depend solely on the concentration gradient. _______ may be involved in bringing substances into cells.

Answer 8

Transport proteins

Question 9

Transport of species into the cell can either be _______ depending on the direction the species is moving relative to its concentration gradient.

Answer 9

passive or active

Question 10

Protein channels and pores are not necessary for all species to enter the cell. Small, uncharged molecules, such as O2, can pass through the membrane by _______.

Answer 10

simple diffusion

Question 11

Although ATP hydrolysis to ADP and phosphate is one energy source for active transport processes, the energy stored in the ________ gradient for a second species is used in some cases to provide the energy for transport of the first species.

Answer 11

electrochemical

Question 12

For membranes, the ______ head groups are in contact with water, and the ______ tails lie in the interior

Answer 12

polar
nonpolar

Question 13

Proteins ______ in the lipid bilayers rather than being sandwiched between them.

Answer 13

“float”

Question 14

Lipid bilayers are an important component of ______.

Answer 14

membranes

Question 15

Waxes are mixtures of esters of long-chain ______ and long-chain ______.

Answer 15

carboxylic acids
alcohols

Question 16

Waxes are found on the ______ of leaves.

Answer 16

outside

Question 17

Waxes frequently form _______ for plants as well as animals.

Answer 17

protective coatings

Question 18

Lipids can be grouped based on:

having a preponderance of ______ groups.
their _______ in nonpolar solvents.

Answer 18

nonpolar
high solubility

Question 19

Steroids have a ______ consisting of _______. Steroids vary in the functional groups attached to this four-ring core and in the oxidation state of the ring carbons.

Answer 19

four fused ring system
three six-membered rings and one five-membered ring

Question 20

Types of lipids:

Answer 20

Fatty acids
Triacylglycerols
Phospholipids
Glycolipids
Steroids

Question 21

Fatty acids:
Triacylglycerols:
Phospholipids:
Glycolipids:
Steroids:

Answer 21

Fatty acids: simplest, fuels
Triacylglycerols: storage of energy
Phospholipids: membrane
Glycolipids: membrane
Steroids: component of membranes, signaling molecules

Question 22

Fatty acids are classified based on:

Answer 22

length of chain (# of carbons in chain) and #/nature of double bonds

Question 23

Saturated fatty acid means hydrocarbon chain…

Answer 23

has no double bonds
“saturated” with carbons, has as many carbons as possible

Question 24

Unsaturated fatty acid means hydrocarbon chain…

Answer 24

has a double bond

Question 25

18:1(∆9) means…

Answer 25

18 carbons
1 double bond at 9th carbon counting from the carbonyl carbon

Question 26

“Omega-3” means the first double bond is on…

Answer 26

the 3rd carbon from the END of the chain

Question 27

Humans can convert ALA (essential) to…

Answer 27

EPA and DHA

Question 28

Saturated fatty acids solidify _____ and has a relatively _____ melting temperature because…

Answer 28

easily
high
dispersion forces (packed tight)

Question 29

Mixture of saturated and unsaturated fatty acids: acyl chains are liquid, and solidify at a relatively ____ temperature

Answer 29

low
less strong IMFs

Question 30

_______ determines the melting point of fatty acids

Answer 30

of double bonds

Question 31

Adipocytes (fat cells) - The lipid droplet contains ________, and takes up most of the cell volume.

Answer 31

triacylglycerols

Question 32

In fat (or ________), glycerol is esterfied with ______

Answer 32

triacylglyceride
three fatty acids

Question 33

Fat can be used for metabolic ______ because its carbon atoms are _______

Answer 33

energy storage
highly reduced

Question 34

Fat can act as a source for _______ production, and for ______ in organisms

Answer 34

energy or heat
thermal insulation

Question 35

Because of the extremely small polar region, waxes are _______

Answer 35

completely water insoluble

Question 36

Fatty acids are ____ and tend to form ______.

Phospholipids are more _______ and pack together to form ______.

Answer 36

wedge-shaped
spherical micelles

cylindrical
a bilayer structure

Question 37

3 common types of membrane lipids:

Answer 37

Phospholipids
Glycolipids
Cholesterol

Question 38

_______ are the major class of membrane lipids

Answer 38

Phospholipids

Question 39

Phospholipids are composed of four components:

Answer 39

fatty acids (2 or more)
a platform
a phosphate
an alcohol

Question 40

Two common platforms are _____ and ______.

Answer 40

glycerol
sphingosine

Question 41

Phospholipids with a glycerol platform are called ______

Answer 41

phosphoglycerides or
phosphoglycerols

Question 42

The major phospholipids are derived from ______.

Answer 42

phosphatidate

Question 43

On a sphingosine platform, the ____ of Serine can react with a fatty acid and _____ of Serine is where phosphate will bond

Answer 43

NH3+
OH

Question 44

Glycolipids are _________ lipids.

Answer 44

carbohydrate-containing

Question 45

The carbohydrate components of glycolipids are on the _______ of the cell membrane, where they play a role in cell-cell interactions.

Answer 45

extracellular surface (outer leaflet)

Question 46

Some sphingolipids have ______ as head groups

Answer 46

monosaccharides

Question 47

Cholesterol is in a class of compounds called ______

Answer 47

steroids

Question 48

Cholesterol is the most common _____ and plays a role in maintaining _______

Answer 48

steroid
membrane fluidity

Question 49

Spontaneous formation of bilayers is driven by the _______.

Answer 49

hydrophobic effect.

Question 50

Saturated fatty acid chains have ____ packing, therefore ______ fluid

Answer 50

tighter
less

Question 51

Unsaturated fatty acid chains have _____ packing, therefore ______ fluid

Answer 51

looser packing
more

Question 52

Cholesterol disrupts ______ packing of fatty acid chains, therefore _____ fluidity but can also complex with lipids and proteins to form a ______, therefore ______ fluidity

Answer 52

straight chain
increasing

“lipid raft”
decreasing

Question 53

Diffusion of lipids in membranes differs according to ______.

Answer 53

direction

Question 54

Transverse diffusion (flip-flop):

Answer 54

Outer to inner leaf
very slow

Question 55

Lateral diffusion

Answer 55

ex. changes position on outer leaf
rapid

Question 56

Integral proteins are also called _____ protein and they go ______

Answer 56

transmembrane
all the way through bilayer

Question 57

Three modes of membrane transport processes:

Answer 57

1) Nonmediated transport
2) Facilitated (passive) transport
3) Facilitated (active) transport

Question 58

1) Nonmediated transport
* Diffusion across a membrane is more rapid for those solutes that are _______, and significantly slower for ______.

Answer 58

hydrophobic (lipophilic)

polar/charged solutes (membranes are effective barriers to the diffusion of polar/charged molecules)

Question 59

Diffusion typically from ____ concentration to _____ concentration

Answer 59

higher, lower

Question 60

2) Facilitated (passive) transport
* Diffusion of certain solutes is accelerated by _______

Answer 60

specific transporter proteins (channels, pores, carriers)

usually polar solutes
still spontaneous

Question 61

3) Facilitated (Active) transport
* Transporter proteins that couple a _______ to achieve transport against a concentration gradient

Answer 61

thermodynamically favorable process

Question 62

For diffusion, where we have the same starting and ending
molecule, the gibbs free energy equation is:

Answer 62

∆G = RTlnQ

Q = final concentration/initial concentration

Question 63

There is a charge difference across the semi-permeable membrane. More _____ inside, more ______ outside

This separation of charge causes a ______ across the membrane space

Answer 63

negative, positive

voltage

Question 64

Free energy equation when there is a cell (membrane potential):

Answer 64

∆Gt = RTln (C2/C1) + ZF∆Ψ

Question 65

Active transport against a concentration gradient can be driven by ______; such direct coupling is seen in _____, such as the ______

Answer 65

ATP hydrolysis
ion pumps
Na + -K+ ATPase

Question 66

Why high release of energy from ATP?

Answer 66

1) separation of negative charges
2) ATP –> ADP + Pi, increase in entropy
3) more resonance from inorganic phosphate, stabilizing

Question 67

What structural features do a triacylglycerol and a phosphatidyl ethanolamine have in common? How do the structures of these two types of lipids differ?

Answer 67

In both types of lipids, glycerol is esterified to carboxylic acids, with three such ester linkages formed in triacylglycerols and two in phosphatidyl ethanolamines. The structural difference comes in the nature of the third ester linkage to glycerol. In phosphatidyl ethanolamines, the third hydroxyl group of glycerol is esterified not to a carboxylic acid but to phosphoric acid. The phosphoric acid moiety is esterified in turn to ethanolamine.

Question 68

What structural features do a sphingomyelin and a phosphatidyl choline have in common? How do the structures of these two types of lipids differ?

Answer 68

Both sphingomyelins and phosphatidylcholines contain phosphoric acid esterified to an amino alcohol, which must be choline in the case of a phosphatidylcholine and may be choline in the case of a sphingomyelin. They differ in the second alcohol to which phosphoric acid is esterified. In phosphatidylcholines, the second alcohol is glycerol, which has also formed ester bonds to two carboxylic acids. In sphingomyelins, the second alcohol is another amino alcohol, sphingosine, which has formed an amide bond to a fatty acid.

Question 69

You have just isolated a pure lipid that contains only sphingosine and a fatty acid. To what class of lipids does it belong?

Answer 69

This lipid is a ceramide, which is one kind of sphingolipid.

Question 70

Sphingolipids contain _____ bonds, as do proteins. Both can have _______ parts, and both can occur in _______, but their functions are different.

Answer 70

amide
hydrophobic and hydrophilic
cell membranes

Question 71

Steroids contain a characteristic ______, which other lipids do not.

Answer 71

fused-ring structure

Question 72

Which is more hydrophilic, cholesterol or phospholipids? Defend your answer.

Answer 72

Phospholipids are more hydrophilic than cholesterol. The phosphate group is charged, and the attached alcohol is charged or polar. These groups interact readily with water. Cholesterol has only a single polar group, an -OH.

Question 73

Succulent plants from arid regions generally have waxy surface coatings. Suggest why such a coating is valuable for the survival of the plant.

Answer 73

The waxy surface coating is a barrier that prevents loss of water.

Question 74

Membranes contain glyco-

Answer 74

glycolipids and glycoproteins.

Question 75

In lipid bilayers, there is an order–disorder transition similar to the melting of a crystal. In a lipid bilayer in which most of the fatty acids are unsaturated, would you expect this transition to occur at a higher temperature, a lower temperature, or the same temperature as it would in a lipid bilayer in which most of the fatty acids are saturated? Why?

Answer 75

The transition temperature is lower in a lipid bilayer with mostly unsaturated fatty acids compared with one with a high percentage of saturated fatty acids. The bilayer with the unsaturated fatty acids is already more disordered than the one with a high percentage of saturated fatty acids.

Question 76

Suggest a reason why animals that live in cold climates tend to have higher proportions of polyunsaturated fatty acid residues in their lipids than do animals that live in warm climates.

Answer 76

The higher percentage of unsaturated fatty acids in membranes in cold climates is an aid to membrane fluidity.

Question 77

Are the relative amounts of cholesterol and phophatidylcholine the same in all the kinds of membranes found in a typical mammalian cell?

Answer 77

The relative amounts of cholesterol and phosphatidylcholine can vary widely in different types of membranes in the same cell

Question 78

Do all proteins associated with membranes span the membrane from one side to another?

Answer 78

Proteins that are associated with membranes do not have to span the membrane. Some can be partially embedded in it, and some associate with the membrane by noncovalent interactions with its exterior.

Question 79

Suppose that you are studying a protein involved in transporting ions in and out of cells. Would you expect to find the nonpolar residues in the interior or the exterior? Why? Would you expect to find the polar residues in the interior or the exterior? Why?

Answer 79

In a protein that spans a membrane, the nonpolar residues are the exterior ones; they interact with the lipids of the cell membrane. The polar residues are in the interior, lining the channel through which the ions enter and leave the cell.

Question 80

Some proteins and lipids undergo ______ along the inner or outer surface of the membrane.

Carbohydrates are ______ bonded to the outside of the membrane.

Answer 80

lateral diffusion
covalently

Question 81

Biological membranes are highly _____ environments. Charged ions tend to be ______ from such environments rather than dissolving in them, as they would have to do to pass through the membrane by simple diffusion.

Answer 81

nonpolar
excluded

Question 82

Compared to unsaturated fatty acids, saturated fatty acids have ________.

Answer 82

Tighter packing of their hydrocarbon chains

Question 83

Integral membrane proteins tend to have a higher concentration of ______ amino acids on their surface

Answer 83

hydrophobic

Question 84

Integral membrane proteins:
Extends through ______ the membrane
Can act as a ______ through the cell membrane

Peripheral Membrane Proteins:
Attaches only at the ______ of a cell’s membrane
_____ associated with the membrane

Answer 84

all or part of
tunnel

surface
Loosely

Question 85

K+ channel is specific for K+ and not for other ions because the channel ______ to the point where large ions cannot pass through.

Answer 85

narrows

Question 86

What would be ∆G in the transport of a negatively charged ion out of cell that has a negative membrane potential? Assume that there is no difference in concentration across the cell membrane.

Answer 86

∆G < 0

a spontaneous process

Question 87

steps of the mechanism of the sodium-potassium ATPase:

Answer 87

3 sodium ions bind
Phosphorylation of an asp residue
Conformational change releases 3 Na+ ions outside of the cell
2 K+ ions bind
Release of the phosphate group
2 potassium ions are released inside the cell

Question 88

For naming fatty acids, delta nomenclature starts counting carbons from _____, whereas omega nomenclature starts counting carbons from ______.

Answer 88

the carbonyl carbon
the end carbon

Question 89

A defining feature of cholesterol is a ______

Answer 89

fused-ring structure
Gonane structure (fused
cyclopentane/cyclohexane rings)

Question 90

A defining feature of phospholipids is a _______

Answer 90

phosphate group

Question 91

Phospholipids have a ______ backbone

Answer 91

glycerol

Question 92

A defining feature of glycolipids is a _______

Answer 92

Sugar (carbohydrate ring)

Question 93

Glycolipids have a _____ backbone

Answer 93

sphingosine

Question 94

The potassium channel has a ‘selectivity filter’ in place that allows the channel to not only be able to allow potassium through, but keep other molecules out. Here are its features that allow it to do so:
- Size: The filter is physically restrictive to molecules _____ than K+.
- Charges in the filter: The filter commonly contains acidic amino acids (not usually shown in diagrams) and also has the ______ of several residues within the filter to repel ______.
- Coordination with carboyl oxygens: We have selected against opposing charges and molecules bigger than K+, but there is a big question mark with the one atom that gets past both of these filters: the sodium ion. The filter selects against sodium due to its smaller atomic radius that has trouble forming coordination bonds with the carbonyl oxygens present within the filter. This causes the sodium to greatly prefer its hydration shell (that cannot fit through the filter), whereas potassium readily forms the
coordination bonds with the carbonyl oxygens and easily gives up its hydration shell, allowing it to pass through the filter.

Answer 94

larger

carbonyl oxygens
anions

Question 95

increased stability = ____ free energy.

Answer 95

lower

Question 96

The hydrolysis of ATP provides substantial energy for organisms. Describe three reasons why.

Answer 96

• Increase in entropy: One molecule becoming two!
• Resonance stabilization of the inorganic phosphate
• Decreased internal repulsion; all of the negative charges from the phosphate groups make the molecule
  unstable due to having many repelling charges near each other

Question 97

The ATPase mechanism of moving Na+ into a cell and K+ out
of a cell. Is this an example of a uniporter, symporter, or antiporter?

Answer 97

This mechanism is an antiporter since it transports two molecules in opposite directions.

Question 98

1) The protein “begins” open to the cytosol side of the membrane with an ATP bound to the protein. Upon 3 sodium ions binding, it can then accept a phosphate group from ATP, releasing ADP.
2) When this phosphate binds to the pump, there is an induced conformational change that causes the protein to now open to the extracellular side of the membrane.
3) The sodium ions will be released. This conformation has binding that is more favorable for potassium ions as opposed to sodium ions.
4) Two potassium ions will now bind to the protein.
5) When the potassium ions bind, another ATP binds, which will cause the protein to let go of the
phosphate. As this happens, the protein will then return to its original form.
6) Once the pump opens back up to the cytosolic side of the membrane, the potassium ions are released and we are back where we started.