Bacterial Transport System

Question 1

What is the structure of most transport proteins in the outer membrane of gram -tve bacteria?

Answer 1

B-barrel structure

Question 2

What is the B-barrel formed of?

Answer 2

8-26 B-strands

Question 3

What are the 3 main entrances for transport across the outer membrane?

Answer 3

Porins
Specific channels
High-affinity transport systems

Question 4

What is the general structure of porins?

Answer 4

Trimeric structure

Question 5

What the most abundant porins in E.coli?

Answer 5

OmpC
OmpF
PhoE

Question 6

Which porins transport cations?

Answer 6

OmpC and OmpF

Question 7

What porins transport anions?

Answer 7

PhoE

Question 8

What are specific channels?

Answer 8

Similar structure to porins, but allow for the transport of specific nutrients (e.g. maltose)

Question 9

Are specific channels passive or active?

Answer 9

Passive, although they accelerate the diffusion of solutes at low concentrations

Question 10

What is an example of a specific channel?

Answer 10

LamB in E. coli, which transports maltose

Question 11

What is the structure of LamB?

Answer 11

Trimeric 18 stranded B-barrel

Question 12

What are some features of high-affinity transport systems?

Answer 12

High higher affinity for their substrates
Transport requires energy (active)

Question 13

What are some examples of substrates transported via high-affinity transport system?

Answer 13

Iron
Vitamin B12

Question 14

How is energy generated for high-affinity transport system?

Answer 14

Proton motive force, by coupling transporters with proteins at inner membrane

Question 15

What is the outer membrane receptor for vitamin B12?

Answer 15

BtuB

Question 16

What is the outer membrane receptor for iron?

Answer 16

FhuA

Question 17

What is the structure of most transport proteins in the inner membrane of bacteria?

Answer 17

A-helix structure

Question 18

What are the 3 class of cytoplasmic membrane-transport systems?

Answer 18

Simple transporters
ABC transporters
Group translocation

Question 19

Are all inner membrane-transporting systems passive?

Answer 19

No, they are all active

Question 20

Where do simple transporters get their energy from?

Answer 20

Proton motive force- secondary active transport

Question 21

Where do ABC transporters get their energy from?

Answer 21

ATP

Question 22

Where does group translocation get its energy from?

Answer 22

PEP

Question 23

What makes up simple transporters?

Answer 23

Single proteins that span the membrane. They are either symport or antiport transporters

Question 24

What is symport transport?

Answer 24

Transport of two molecules in the same direction

Question 25

What is antiport transport?

Answer 25

Transport of two molecules in opposite directions across the membrane

Question 26

What is the LacY permeate transporter?

Answer 26

Symport simple transporter, which transports lactose and H+ in the same direction

Question 27

What is the sodium-proton transporter

Answer 27

Antiport simple transporter, which transports sodium and H+ in opposite directions across the membrane

Question 28

How many ABC transporter does E. coli contain?

Answer 28

Approximately 80

Question 29

What 3 components make up ABC transporters?

Answer 29

Substrate binding domain (SBP) Transmembrane domain protein (TMD) Nucleotide binding domain protein (NBD)

Question 30

What is the role of the SBP in ABC transporters?

Answer 30

SBP binds to substrate using Venus flytrap mechanism, inducing a conformational change SBP interacts with TMD protein (periplasmic end) and releases the substrate

Question 31

What is the role of TMD in ABC transporters?

Answer 31

Substrate is transferred across transmembrane through TMD protein

Question 32

What is the role of NBD in ABC transporters?

Answer 32

Energy for transfer is generated by hydrolysis of ATP by NBD protein (acts as ATPase)

Question 33

What is group translocation made up of?

Answer 33

A series of proteins (e.g. phosphotransferase system of E. coli consists of 24 proteins )

Question 34

What molecules are group translocated?

Answer 34

Commonly sugars like fructose, glucose and mannose

Question 35

How does group translocation work?

Answer 35

A series of proteins pass a phosphate group down a chain through alternating phosphorylation and dephosphorylation steps. The final membrane-spanning transporter uses this phosphate to chemically modify the sugar (e.g. phosphorylate glucose) as it is transported into the cell.