Cell membrane function and transport systems Flashcards
What is the function of the cell membrane?
Permeability barrier. Controls what goes in and out of the cell
What things can’t cross the membrane without help from proteins?
Polar things, charged, water
What is the proton motive force?
A proton gradient
How is the proton motive force created?
By metabolism. Water is dissociated and the proton is pumped out while the OH- stays inside
What do bacteria use the proton motive force for?
Energy source. It doesn’t need to be converted to ATP before it can be used
What types of proteins will be anchored in the membrane?
Transport proteins, proteins for metabolism like ETC proteins, motility proteins
What type of transport do bacteria use the vast majority of the time?
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
What are 3 properties of transport proteins?
Saturation effect, high specificity, their production is highly regulated
What is the saturation effect?
The point where adding more substrate doesn’t increase the rate of transport because all proteins are in use
Does transporter saturation occur at low substrate concentrations or high substrate concentrations in bacteria?
Low
Are bacterial transport proteins high affinity or low affinity?
High affinity
Why do bacterial transport proteins become saturated at low substrate concentrations?
Takes advantage of any nutrients that come by. Would be wasteful to produce tons of transport proteins for extremely rare high nutrient situations
What does it mean when a transporter has high specificity?
They only bring in one thing or a few very similar molecules
Why is a highly specific transporter advantaegeous?
Better regulation and less chance of accidentally bringing in something toxic
Why is having the production of transport proteins highly regulated advantageous?
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
What are the 3 systems of active transport in bacteria?
Simple transport, group translocation, ABC transporters
What are the 3 similarities between simple transport, group translocation, and ABC transporters?
- All are active transport and use energy
- All contain a membrane-spanning channel protein with the same structure
- Channel is gated
What is the structure of the membrane spanning channel protein found in all 3 active transport systems?
12 transmembrane helices with a hole in the middle lined with hydrophilic AA
Why aren’t the channels open all the time?
Would let toxins in and dissipate the PMF
What causes the channel proteins to open?
The substrate binds and causes a conformation change to let the substrate in, then closes again
What are the 2 differences between simple transport, group translocation, and ABC transporters?
Energy source and the number of proteins involved
How many proteins are involved in simple transport?
One. Just the membrane spanning channel protein
What is the energy source of simple transport?
PMF
How does the energy get linked with the transporter in simple transport?
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
What are the 2 types of simple transport?
Symport and antiport
What are symports? What are they for?
Both proton and substrate go into the cell in the same direction. Used for pumping things in
What are antiports? What are they for?
Proton comes in and substrate goes out, they go in opposite directions. Used for pumping things out
How many proteins are involved in group translocation?
- The channel and 4 others involved in energy transfer
What is the energy source of group translocation?
Energy-rich metabolites (high energy intermediates)
What do the helper proteins do in group translocation?
Transfer the phosphate from the the high-energy metabolic intermediate to each other then the transporter
Do the helper proteins only function for one group translocation system?
No, they aren’t specific and can work in multiple systems
How does group translocation work?
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
What are ABC transporters?
ATP-binding-cassette
What is the energy source of ABC transporters?
ATP
How many proteins are involved in ABC transporters? What are they
- The substrate binding protein, the membrane-spanning channel, and an ATP-hydrolyzing protein
How do ABC transporters work?
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
Where is the substrate binding protein of the ABC transporters found?
Outside the cell floating around or anchored in the membrane
Where is the ATP hydrolyzing protein of the ABC transporters found?
Inside the cell in the cytoplasm
