Membrane Transport and Structure

Question 1

Give 4 realistic features of the fluid mosaic model

Answer 1

• Crowded bilayer
• Patchwork appearance
• Local bilayer distortion
• Protein complexes

Question 2

Why do lipids spontaneously self-associate?

Answer 2

The hydrophobic effect and van der Waals interactions between the fatty acid tails

Question 3

What is one of the main components of many membranes?

Answer 3

Glycerophospholipids

Question 4

Why is cholesterol important in membranes?

Answer 4

Modulates packing of lipids and fluidity of membrane

Question 5

Give the 4 ways lipids can move in a membrane

Answer 5

• flip-flop from one side of membrane to the other
• lipids diffuse laterally (movement left or right in the same leaflet)
• rotate freely around their long axis
• hydrocarbon chains are flexible and dynamic so wobble

Question 6

What is the transition temperature of a membrane?

Answer 6

The temperature at which bilayers change from a fluid to a rigid gel phase

Question 7

What is the effect of shorter chains or double bonds in phospholipids on transition temperature?

Answer 7

It lowers it

Question 8

How is lateral diffusion affected by membranes being in the gel phase?

Answer 8

It is greatly reduced

Question 9

Name the 2 enzymes involved in the maintenance of membrane asymmetry

Answer 9

Flippase and floppase

Question 10

Give an example of a lipid transported by flippase

Answer 10

Phosphatidylserine

Question 11

What do flippase and floppase use as a source of energy?

Answer 11

ATP hydrolysis

Question 12

Which direction does floppase move lipids?

Answer 12

From the inner to the outer leaflet (against conc. gradient)

Question 13

Which direction does flippase move membrane lipids?

Answer 13

From outer to inner leaflet (against conc. gradient)

Question 14

Give an example of a lipid moved by floppase

Answer 14

Sphingolipid

Question 16

Are integral membrane proteins generally soluble in aqueous buffers?

Answer 16

No

Question 17

What is the only way integral membrane proteins can be separated from membranes?

Answer 17

By using agents which disrupt membranes

Question 18

Are peripheral membrane proteins often soluble in aqueous buffers?

Answer 18

Yes

Question 19

How are peripheral membrane proteins bound?

Answer 19

To the surface only via binding to integral membrane proteins and/or directly with the lipid headgroup regions

Question 20

What is the typical structure of integral membrane proteins?

Answer 20

• α-helical or ß-barrel
• Structured or unstructured loops outside the membrane

Question 21

Which is the more common structure for integral membrane proteins?

Answer 21

α-helical

Question 22

Where are ß-barrel integral membrane proteins found?

Answer 22

In bacterial outermembranes, mitochondria, and chloroplasts

Question 23

What type of amino acids do integral membrane proteins contain a lot of?

Answer 23

Hydrophobic

Question 24

What is the typical length of an α-helix?

Answer 24

20-25 amino acids

Question 25

How can α-helices be predicted?

Answer 25

The prescence of a string of hydrophobic amino acids in the sequence

Question 26

What types of amino acids are found in ß sheets?

Answer 26

Alternating polar and hydrophobic amino acids

Question 27

Are all membranes asymmetric?

Answer 27

No but many are

Question 28

What is the difference between a transporter and a channel?

Answer 28

A transporter transports molecules down/against a concentration gradient whereas a channel only allows for diffusion down a concentration gradient

Question 29

What is the effect of increasing concentration of the transported molecule on rate of transport in channel proteins?

Answer 29

It increases proportionally to the increase in concentration

Question 30

What is the effect of increasing concentration of the transported molecule on rate of transport in transporters?

Answer 30

It increases but plateaus off (follows Michaelis-Mensen kinetics)

Question 31

Where do solute transporters get their energy to transport molecules against a concentration gradient from?

Answer 31

The movement of one solute from [high] to [low] aka cotransport

Question 32

What are the 3 types of transporter?

Answer 32

* Uniport * Symport * Antiport

Question 33

Describe the movement of a symport transporter

Answer 33

Question 34

Describe the direction of an antiport transporter

Answer 34

Question 35

The hydrolysis of 1ATP moves what in ATPase?

Answer 35

* 3Na+ * 2K+

Question 36

How many Na+ are moved out of a cell for every 2k+ moved in?

Answer 36

3

Question 37

How many K+ are moved in for every 3 Na+ moved out?

Answer 37

2

Question 38

Briefly outline the structure of ATPase

Answer 38

The region of binding and hydrolysis of ATP is distinct from the region through which ions travel

Question 39

What does the F in the Nerst equation represent?

Answer 39

The Faraday constant

Question 40

Give an example of sodium transporters in health and disease

Answer 40

* Glucose uptake depends on Na+:glucose symporters * These transporters promote te readsorption of glucose from the bloodstream * Inhibitors of SGLTs can be used to treat diabetes

Question 41

Give an example of a proton-coupled transporter

Answer 41

Lactose Permease

Question 42

Why type of transporter is lactose permease? Outline the movement of the molecules

Answer 42

Symport (H+ are moved from high to low conc. whilst lactose is moved from low to high)

Question 43

What is the mechanism for LacY? (lactose permease)

Answer 43

* Never fully opens a pore (Sealed by a rocker-switch mechanism) * Position of an H bond moves in order to allow for a conformational change in shape

Question 44

Give the features of ABC transporters

Answer 44

* Use ATP binding and hydrolysis to directly power transport * Both export and import substances

Question 45

Give an example of ABC transporters in context of health and disease

Answer 45

* MDR1 is a transporter whose natural function is to protect cells from toxic compounds * It is a problem as it pumps drugs out of a cell * Involved in aquired multidrug resistance in cancer

Question 46

How does light-activated transport work?

Answer 46

* Bacteriorhodopsin absorbs light at a certain wavelength * Upon light activation, it moved H+ across the membrane and generates a proton motive force