Chapter 11

Question 1

In cell membranes, why are there two chains coming off the polar heads instead of one?

Answer 1

Because one chain would create a micelle, but two chains creates the lipid bilayer

Question 2

Phsophatidylcholine and sphingomyelin are the major amphipathic _______ lipids

Answer 2

Membrane

Question 3

Charged molecules have low permeability in the lipid bilayer, but water passes easily because _____

Answer 3

There is so much of it that it pushes its way through the membrane

Question 4

Why is the distribution of phospholipids asymmetric?

Answer 4

The distribution depends on the location of the membrane and its intended function. Altering this will have biological consequences

Question 5

What are the differences between an integral and peripheral protein?

Answer 5

Integral proteins are found on the inside of the membrane, so they will be composed mostly of NP AA’s so they are able to interact with the hydrophobic core membrane.

Peripheral membranes are polar so they can perform h-bonding or electrostatic interactions to other molecules. They are covalently anchored to the membrane itself through lipid chains

Question 6

Integral proteins are purified with ______ while peripheral proteins are purified with _____

Answer 6

Detergents

Salts

Question 7

The sugars linked to peripheral proteins can be cleaved with ______

Answer 7

Glycosidases

Question 8

Integral proteins are held in membranes via _____ interactions

Answer 8

Hydrophobic

Question 9

A positive hydropathy plot means the AA’s are ____ , while a negative plot means the AA’s are _____

Answer 9

Non-polar

Polar

Question 10

When reading a hydropathy plot, there must be at least ___ AA’s in a row to constitute an integral protein

Answer 10

20

Question 11

When reading a hydropathy plots, the number of AA sequences (peaks) correlates with ______

Answer 11

The number of times the protein crosses the membrane

Question 12

Why can’t a hydropathy plot be used for a beta barrel integral protein?

Answer 12

Because the beta sheet (and therefore the beta barrel) is more elongated than the alpha helix, it only needs about 7-9 residues crossing the membrane to be an integral protein. This makes it too difficult to judge when the protein actually crosses the membrane, since this is such a small amount

Question 13

What is the fluid mosaic model?

Answer 13

The fluid mosaic model suggests that cell membranes are made up of many different molecules that are constantly in motion. This movement helps the cell maintain its role as a barrier, and also makes it semi-permeable

Question 14

How did the FRAP experiment demonstrate the fluid mosaic model and membrane dynamics?

Answer 14

When the laser bleached a certain area of the bacteria, that area was slowly replaced with lipids surrounding it. This showed that the molecules in the membrane are able to move around, because if they were static the bleached area would not have been able to recover

Question 15

How do membranes change with temperature?

Answer 15

When the temperatures are low, the membrane enters the paracrystalline state, where the molecules are not moving and the membrane becomes solid

When the temperatures are high, the membrane becomes fluid and everything is able to move normally

Question 16

How does the composition of fatty acids in a membrane that exists at low temperatures differ from one that exists at higher temperatures?

Answer 16

In membranes that exist at lower temperatures, there will be more monounsaturated fatty acids, because they are not able to pack as tightly and create fluidity.

In membranes that exist at higher temperatures, there will be more unsaturated fatty acids because they are able to pack tightly. This creates fluidity, and also helps keep the membrane from falling apart.

Question 17

_____ diffusion is significantly slower than _____ diffusion

Answer 17

Transverse

Lateral

Question 18

What is the purpose of the lipid raft?

Answer 18

The lipid raft is composed of lipids and cholesterol that are longer than normal in order to anchor proteins whose chain would not fit in the normal membrane.

Question 19

How are proteins anchored to the cell membrane?

Answer 19

They are anchored by a lipid chain that links covalently to the cell membrane

Question 20

Flippase is used when the lipids are moved from _______ to _______

Answer 20

Outside to inside

Question 21

Floppase is used when the lipids are moved from _____ to _____

Answer 21

Inside to outside

Question 22

Scramblase is used when moving lipids in _____

Answer 22

Either direction (inside to outside or outside to inside)

Question 23

Any diffusion that does not require energy (ATP) will go _____ the gradient

Answer 23

Down

Question 24

How do transporters lower the activation energy for diffusion?

Answer 24

They create an environment that is favorable for a polar molecule so that it doesn’t need to shed its hydration layer to get through the membrane.

Question 25

Why are carriers saturable while channels are not?

Answer 25

Transporters act like an enzyme and bind to their specified substrates. This means that, like enzyme kinetics, they will have a Vmax. They are able to move somewhat fast, but are limited by the amount of trasnporter available (because you can’t bind to what isn’t there)

Channels are either open or closed, so they are not saturable. They don’t have a Vmax and are able to achieve the diffusion rate of 10^8 because they depend only on the ion itself being there (there isn’t anything to bind to, so the diffusion rate isn’t limited)

Question 26

How do carriers compare to channels?

Answer 26

Transporters act like enzymes and bind with high stereospecificity. Because they bind to the substrate, they are saturable, have a Vmax, and transport at rates lower than the diffusion limit. This is because diffusion rate is limited by both the substrate having to bind and the conformational changes the membrane must make to accommodate the transporter. They can also be either passive or active

Channels are either closed or open, and because they do not bind to anything, they are not saturable and are able to diffuse close to diffusion limit. They do not need to bind anything, so they can diffuse as fast as the ion takes to travel through the channel

Question 27

How does simple diffusion work?

Answer 27

Non-polar molecules that are able to permeate the membrane by themselves

Question 28

Of the two types of cotransporters, symport transports _____ and antiport transports _______

Answer 28

2 things in the same direction

2 things in the opposite direction

Question 29

What is the process by which P-type ATPase works?

Answer 29

When the ion binds to the transmembrane helices, the N-domain takes a phosphate from ATP and gives it to the P domain to phosphorylate the aspartate. This causes a conformational change that is relayed by the A domain, and the ion is released to the other side of the cell. Once that’s done, the phosphate is also released and the enzyme can go back to its native conformation

Question 30

Instead of using ATP, secondary active transport utilizes _______

Answer 30

The gradient created from the active transport of another ion

Sometimes it requires the use of another pump (ex. lactose permease)

Question 31

Ion channels can be ______ or ______ gated

Answer 31

Ligand –> charges from AA’s are used to prevent the wrong thing from entering the channel (ex. K+ channel)

Voltage –> a change in the transmembrane voltage causes the helices to change their conformation