BIOL 221 Lec 6 Transporters

An active transport uniport uses what source of energy to bring molecules across the cell

membrane

The voltage potential (electrical charge) across the membrane

A primary active transporter is essentially irreversible (it only transports molecules in one

direction) because..

It requires a protein to bond from the outside before the channel can open

Which of the following is NOT true of the PTS (phosphotransferase) transport system?

It involves direct transfer of a phosphate from ATP to glucose

Why are we interested in studying type III secretion systems?

They are often associated with insertion of toxins directly into eukaryotic cells

What type of transport is carried out by the PTS (phosphotransferase system)?

Import of sugars

A hallmark of a type III secretion system is...

Secretion only once contact has been made with a host cell membrane receptor

Why does passive transport require energy?

To open facilitated diffusion channels in the membrane

How does the MFS antiport pump Na + out of the cell?

It uses the energy of the proton gradient

Which of the following is a characteristic of a bacterial type II export system?

Use of a leader peptide (signal sequence) to determine which proteins to secrete

Why does the PTS (phosphotransferase system) use a phosphorelay mechanism

To sense the available carbohydrate and regulate cell responses accordingly

Which of the following is NOT a feature of the “gated rocker-switch” mechanism for transporter

function?

Plug in transport channel moved aside by energy from ATP

Why is the phosphorelay mechanism involved in sugar transport in bacteria

Each protein in the relay can be used to regulate other cell processes based on the presence

or absence of sugar in the environment

Structurally, what does it mean that transport of solute #1 with its gradient allows transport of

solute #2 against its gradient?

Solute #1 holds the transporter open long enough for solute #2 to bind

\

There is currently much interest in studying efflux pumps that bacteria use to eliminate toxins and antibiotics. What is one characteristic of these efflux pumps?

The toxin is secreted through bacterial membranes in 1 step

Which of the following is NOT a feature found in Type II secretion systems (T2SS)?

Transport is blocked until the bacterium contacts another cell

What special feature of ABC import transporters male them essentially irreversible?

A protein that binds solute before it signals from the periplasm for the transporter to open

What makes passive transport “passive”?

It is unable to concentrate a solute against a chemical gradient

Some transporters have gates. What is the purpose of the gates in gated transporters

To increase the accumulation ration by preventing reverse transport

Which of the following is a unique feature of the PTS transport system?

A relay that allows many opportunities for regulation of the transporter

What is the “Sec translocon”?

A transporter that inserts proteins with a signal sequence through the inner membrane

The most evolutionary primitive rocker-switch model for transport proteins requires...

A transporter with two alternative conformations

A bacterium is growing in a medium with a [K + ] of 1 mM. The bacterium uses a uniport to

accumulate K + to 10mM concentration inside the cell. What is the energy for this transport?

The membrane potential

Which of the following is NOT a characteristic of the bacterial PTS transport system?

It can be used to import and export a wide variety of solutes

What is the purpose of a molecular chaperone during protein secretion in bacteria?

It keeps a protein in an unfolded conformation until transport

A certain bacterium uses proline as an osmoprotectant. What sort of proline transporter serves this purpose best? Why?

An ABC system because of a protein that prevents reverse transport

Which of the following is a similarity between Type II and Type III secretion systems?

Use of ATP hydrolysis as the energy source for transport

How is the energy of a H + gradient most directly used by the cell to uptake glucose?

Binding of a H + holds a transporter open until glucose also binds

Which of the following is NOT a feature of facilitated diffusion channels, such as aquaporins?

They transport solutes in only 1 direction

The drug valinomycin affects the membrane potential, but not the ∆pH. Which of the following

transporters would be most affected by treatment with valinomycin?

A lysine uniport

What is the role of the periplasmic binding protein in ABC uptake systems?

It blocks reverse transport of the solute

All of the following are advantages of the PTS system, EXCEPT...

It is an efficient transfer of phosphate from ATP directly to glucose

What do bacterial ABC drug efflux pumps and Type III secretory systems have in common?

Neither involves a periplasmic intermediate