Cell membrane function and transport systems

Question 1

What is the function of the cell membrane?

Answer 1

Permeability barrier. Controls what goes in and out of the cell

Question 2

What things can’t cross the membrane without help from proteins?

Answer 2

Polar things, charged, water

Question 3

What is the proton motive force?

Answer 3

A proton gradient

Question 4

How is the proton motive force created?

Answer 4

By metabolism. Water is dissociated and the proton is pumped out while the OH- stays inside

Question 5

What do bacteria use the proton motive force for?

Answer 5

Energy source. It doesn’t need to be converted to ATP before it can be used

Question 6

What types of proteins will be anchored in the membrane?

Answer 6

Transport proteins, proteins for metabolism like ETC proteins, motility proteins

Question 7

What type of transport do bacteria use the vast majority of the time?

Answer 7

Active transport. Most bacteria live in nutrient poor environments and the nutrient concentration is higher in the cell than outside. The cell needs to move solutes against their gradients

Question 8

What are 3 properties of transport proteins?

Answer 8

Saturation effect, high specificity, their production is highly regulated

Question 9

What is the saturation effect?

Answer 9

The point where adding more substrate doesn’t increase the rate of transport because all proteins are in use

Question 10

Does transporter saturation occur at low substrate concentrations or high substrate concentrations in bacteria?

Answer 10

Low

Question 11

Are bacterial transport proteins high affinity or low affinity?

Answer 11

High affinity

Question 12

Why do bacterial transport proteins become saturated at low substrate concentrations?

Answer 12

Takes advantage of any nutrients that come by. Would be wasteful to produce tons of transport proteins for extremely rare high nutrient situations

Question 13

What does it mean when a transporter has high specificity?

Answer 13

They only bring in one thing or a few very similar molecules

Question 14

Why is a highly specific transporter advantaegeous?

Answer 14

Better regulation and less chance of accidentally bringing in something toxic

Question 15

Why is having the production of transport proteins highly regulated advantageous?

Answer 15

You only make transporters that are needed. Only transporters for nutrients that are needed by the cell and are present in the environment are produced

Question 16

What are the 3 systems of active transport in bacteria?

Answer 16

Simple transport, group translocation, ABC transporters

Question 17

What are the 3 similarities between simple transport, group translocation, and ABC transporters?

Answer 17

1. All are active transport and use energy
2. All contain a membrane-spanning channel protein with the same structure
3. Channel is gated

Question 18

What is the structure of the membrane spanning channel protein found in all 3 active transport systems?

Answer 18

12 transmembrane helices with a hole in the middle lined with hydrophilic AA

Question 19

Why aren’t the channels open all the time?

Answer 19

Would let toxins in and dissipate the PMF

Question 20

What causes the channel proteins to open?

Answer 20

The substrate binds and causes a conformation change to let the substrate in, then closes again

Question 21

What are the 2 differences between simple transport, group translocation, and ABC transporters?

Answer 21

Energy source and the number of proteins involved

Question 22

How many proteins are involved in simple transport?

Answer 22

One. Just the membrane spanning channel protein

Question 23

What is the energy source of simple transport?

Answer 23

PMF

Question 24

How does the energy get linked with the transporter in simple transport?

Answer 24

Is a coupled system. The energy released from the proton travelling down its concentration gradient and is coupled to the transporter to power the transport of the substrate

Question 25

What are the 2 types of simple transport?

Answer 25

Symport and antiport

Question 26

What are symports? What are they for?

Answer 26

Both proton and substrate go into the cell in the same direction. Used for pumping things in

Question 27

What are antiports? What are they for?

Answer 27

Proton comes in and substrate goes out, they go in opposite directions. Used for pumping things out

Question 28

How many proteins are involved in group translocation?

Answer 28

5. The channel and 4 others involved in energy transfer

Question 29

What is the energy source of group translocation?

Answer 29

Energy-rich metabolites (high energy intermediates)

Question 30

What do the helper proteins do in group translocation?

Answer 30

Transfer the phosphate from the the high-energy metabolic intermediate to each other then the transporter

Question 31

Do the helper proteins only function for one group translocation system?

Answer 31

No, they aren’t specific and can work in multiple systems

Question 32

How does group translocation work?

Answer 32

Helper protein 1 takes a phosphate off PEP, then transfers it to helper protein 2, then helper protein 3, then helper protein 4. Helper protein 4 transfers the energy to the transporter to bring the substrate in and sticks the phosphate onto the incoming glucose

Question 33

What are ABC transporters?

Answer 33

ATP-binding-cassette

Question 34

What is the energy source of ABC transporters?

Answer 34

ATP

Question 35

How many proteins are involved in ABC transporters? What are they

Answer 35

3. The substrate binding protein, the membrane-spanning channel, and an ATP-hydrolyzing protein

Question 36

How do ABC transporters work?

Answer 36

Substrate binding protein will bind to the substrate and bring it to the transporter. The ATP hydrolyzing protein then hydrolyzes ATP and causes a conformation change in the transporter, which brings in the substrate

Question 37

Where is the substrate binding protein of the ABC transporters found?

Answer 37

Outside the cell floating around or anchored in the membrane

Question 38

Where is the ATP hydrolyzing protein of the ABC transporters found?

Answer 38

Inside the cell in the cytoplasm