Nutrient Uptake into Bacterial Cells

Question 1

Cytoplasmic membrane

Answer 1

-only small uncharges non polar molecules move freely across the cytoplasmic membrane
-some molecules can cross at a meaningful rate but significantly hindered by membrane (H2O, glycerol, some AA)
-the membrane is essentially impermeable to many other molecules (large and or charged molecules)
-cell dedicated significant resources to ensuring that molecules it needs get in but harmful substances do not

Question 2

passive transport

Answer 2

-no energy
-down concentration gradient
-simple diffusion and facilitated diffusion

Question 3

active transport

Answer 3

-needs energy
-against concentration gradient
-simple transport, ABC transporters and group transporters

Question 4

diffusion

Answer 4

net movement of chemical down concentration gradient
-entropically favourable
-no energy
-concentration gradient represents source of potential energy

Question 5

osmosis

Answer 5

diffusion of water through selectively permeable membrane along its concetration gradient

Question 6

facilitated diffusion

Answer 6

-diffusion of moelcules across the membrane via a membrane protein that acts as a channel (porins of membrane)
-can be specific recognition element for specific molecules (carrier proteins)
-can be non specific allow only molecules of certain size or charge (channel proteins)
-generally the production and or activity of these channels is usually regulated by the cell

Question 7

where does the enrgy for active transport come from

Answer 7

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

Question 8

simple transport

Answer 8

-symporters and antiporters
-symporters and antiporters use energy stored in gradients (PMF) to power transport of a different molecule against it gradient

Question 9

sodium proton antiporter

Answer 9

-exchange protons fro NA+ ions
-main purpose for homeostasis
-expel Na from cell under high salt conditions
-lower pH of cell under alkaline conditions

Question 10

lac permease symporter

Answer 10

-PMF is exploited to drive the uptake of lactose and some related disaccharides into the cell

Question 11

group translocation

Answer 11

-active transport
-transported substance is bound by transporter and chemically modified during transport
-Ex: glucose –> G6P in the phosphotranferase system
-energy provided by hydrolysis of PEP (phosphoenolpyruvate)
-phosphorylation of the sugar molecule is helpful metabolically
-specific and non specific components

Question 12

ABC transporters

Answer 12

-Active transport
-use ATP to transport across the cytoplasmic membrane
-one of largest oldest gene families found from bacteria to humans

Question 13

3 components of ABC transporters

Answer 13

-2 ATPase domains (proteins) provide energy
-Transmembrane domains (protein) provide selective channel
-substrate binding protein binds molecule with high afffinity and deliverys it to the channel

Question 14

substrate binding proteins

Answer 14

-periplasmic binding proteins
-prokaryotic ABC transporters are best stufied in gram neg which use periplasmic binding proteins to capture their ligand within the periplasm
-in archea and gram pos baxteria (no OM) the substrate binding protein is often tethered to the cytoplasmic membrane

Question 15

Vitamin B 12 ABC transporter

Answer 15

-B12 is large complicated precious and scarce
-too large to diffuse through proins
-E coli used transporter to efficiently take up B12
-OM barrel protein BtuB binds B12 with high affinity, transports across OM using energy from TonB complex (PMF)
-Bt8CD-F is the ABC transpirter
-BtuF has very high affinity for B12

Question 16

what else is taken up similar to B12

Answer 16

iron
-iron binding sidrophores are taken up in an analougous manner