Topic 2-L6 - Nutrient uptake into bacterial cells

Question 1

The cytoplasmic membrane:

Answer 1

The gatekeeper of the cell

Question 2

Which molecules can move freely across the cytoplasmic membrane?

Answer 2

Small, non polar, uncharged molecules

Question 3

Some molecules can cross the CPM at a

Answer 3

meaningful rate (but significantly
hindered by the membrane)

Question 4

The CPM is impermeable to

Answer 4

Large, polar, charged molecules

Question 5

How mcolueslenter bacterial cells

Answer 5

Passive transport (no E)

Active transport (uses E)

Question 6

Passive transport

Answer 6

• simple diffusion

- facilitated diffusion

Question 7

Active transport

Answer 7

• simple transport
• ABC transporters
• group transport

Question 8

Diffusion:

Answer 8

The net movement of a chemical down it’s concentration gradient (from area of high concentration to area of low concentration).

• Entropically favorable!

Question 9

Osmosis is the

Answer 9

diffusion of water along its concentration gradient. (A low concentration of solutes = a high concentration of water)

Question 10

Facilitation diffusion:

Answer 10

Diffusion of molecules across the membrane via a membrane protein (permease) that acts as a channel. Porins of OM.

• can be specific or non specific

Question 11

Any time a molecule is transported against its concentration gradient, this requires energy.
This can come from

Answer 11

stored chemical energy (e.g. ATP hydrolysis) or from dissipation of another concentration gradient (transporting another molecule along its concentration gradient)

Question 12

Symporters & antiporters use the energy stored in

Answer 12

chemical gradients to power the transport of a different molecule against its gradient

Question 13

Symport:

Answer 13

Both molecules travel same direction

Question 14

Antiport:

Answer 14

One molecule in, the other out

Question 15

Symporters and antiporters often use

Answer 15

proton motive force (H+ gradient)

Question 16

Sodium proton antiporter

Answer 16

Exchanges protons (dissipation of proton gradient) for Na+ ions.

• Expel Na+ from cell under high salt conditions
• Lower pH of cell under alkaline conditions

Question 17

Lac permease antiporter

Answer 17

Proton motive force is exploited to drive the uptake of lactose and some related disaccharides (high energy food source) into the cell

Question 18

Group translocation

Answer 18

ACTIVE TRANPORT

Transported substance is bound by a transporter and is chemically modified during transport

Question 19

Example of group translocation

Answer 19

glucose uptake using the phosphotransferase system.

Question 20

glucose uptake using the phosphotransferase system.

Answer 20

Energy provided by hydrolysis of high energy phosphate in phosphoenolpyruvate (PEP)

• An important feature of this translocation mechanism is that the membrane is impermeable to the phosphorylated sugar molecule – remains in cell

Question 21

ABC transporters

Answer 21

ATP binding cassette (ABC transporters) use ATP to power the transport of substances across the cytoplasmic membrane

Question 22

ABC transporters proteins involved

Answer 22

• 2 ATPase domains (proteins) provide energy
• Transmembrane domain(s) (proteins) provides selective channel
• Substrate binding protein binds molecule with high affinity and delivers it to the channel

Question 23

Prokaryotic ABC transporters are best studied in

Answer 23

Gram-negative bacteria – which use “periplasmic binding proteins” to capture their ligand within the periplasm

Question 24

In archaea and Gram positive bacteria (lack OM) – the substrate binding protein is tethered to the

Answer 24

cytoplasmic membrane

Question 25

Vitamin B12 is very

Answer 25

Large, precious, and too big to diffuse through porins.

Question 26

How does vitamin B12 enter bacterial cells

Answer 26

ABC transporters

Question 27

How does B12 use ABC transporters to enter cell

Answer 27

OM barrel protein BtuB binds B12 with high affinity, transports across OM using energy from To n B complex (via proton motive force)

Question 28

Iron-binding siderophores

Answer 28

(molecules secreted to capture precious iron) are taken up in a synonymous manner as B12