Translocation Flashcards
On what basis are translocation systems based on?
The source of energy which is used to support accumulation of solute within the cell
Why is it not feasible for most translocation systems to comprise a freely open channel through the membrane?
The substrate would be able to pass through the channel freely in both directions, so accumulation to a higher intracellular concentration would be impossible
Which translocation system is most limited in terms of solute concentration inside the cell? What can support the highest?
Facilitated diffusion because it can only achieve an equilibrium of internal and external solute concentration
ATP-dependent transport (ABC transporters) can achieve concentration gradients of up to 10^5 fold
What is unique about the PEP-dependent phosphotransferase system?
It both transports and simultaneously phosphorylates its substrates
Why is the PEP-dependent system common in anaerobes (especially facultative and obligate)?
Since the two energy-requiring steps are achieved in a single reaction, it is an energy-efficient system, so it is found in anaerobic bacteria which don’t generate much ATP via their fermentative metabolism
What is the best known group translocation system?
PEP-dependent phosphotransferase system
What is unusual about E. coli’s TRAP system?
It is shock-sensitive but is not an ATP-dependent transport system, instead it operates by H+ symport
What is unusual about E. coli’s Kdp system?
It is an ATP-dependent system but is not shock-sensitive, for transporting K+
What is the difference between primary and secondary translocation?
In primary translocation, translocation is directly linked to a biochemical reaction
In secondary translocation, translocation is linked to metabolism indirectly via an ion gradient
In primary translocation, what is the difference between group translocation and enzyme-linked solute translocation?
In group translocation, chemical modification occurs concurrently with translocation
In enzyme-linked solute translocation, substrate is not modified, but translocation is the result of a biochemical reaction
What is meant by shock sensitive?
It refers to systems where a periplasmic binding protein is involved
How do periplasmic binding proteins work?
They bind the substrate in the periplasm, then interact with transport proteins in the cytoplasmic membrane. Substrate is released and translocated into the cytoplasm
Binding protein does not cross the cytoplasmic membrane
