Bacterial Transport System Flashcards

1
Q

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

A

B-barrel structure

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2
Q

What is the B-barrel formed of?

A

8-26 B-strands

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3
Q

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

A

Porins
Specific channels
High-affinity transport systems

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4
Q

What is the general structure of porins?

A

Trimeric structure

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5
Q

What the most abundant porins in E.coli?

A

OmpC
OmpF
PhoE

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6
Q

Which porins transport cations?

A

OmpC and OmpF

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7
Q

What porins transport anions?

A

PhoE

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8
Q

What are specific channels?

A

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

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9
Q

Are specific channels passive or active?

A

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

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10
Q

What is an example of a specific channel?

A

LamB in E. coli, which transports maltose

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11
Q

What is the structure of LamB?

A

Trimeric 18 stranded B-barrel

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12
Q

What are some features of high-affinity transport systems?

A

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

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13
Q

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

A

Iron
Vitamin B12

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14
Q

How is energy generated for high-affinity transport system?

A

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

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15
Q

What is the outer membrane receptor for vitamin B12?

A

BtuB

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16
Q

What is the outer membrane receptor for iron?

17
Q

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

A

A-helix structure

18
Q

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

A

Simple transporters
ABC transporters
Group translocation

19
Q

Are all inner membrane-transporting systems passive?

A

No, they are all active

20
Q

Where do simple transporters get their energy from?

A

Proton motive force- secondary active transport

21
Q

Where do ABC transporters get their energy from?

22
Q

Where does group translocation get its energy from?

23
Q

What makes up simple transporters?

A

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

24
Q

What is symport transport?

A

Transport of two molecules in the same direction

25
Q

What is antiport transport?

A

Transport of two molecules in opposite directions across the membrane

26
Q

What is the LacY permeate transporter?

A

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

27
Q

What is the sodium-proton transporter

A

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

28
Q

How many ABC transporter does E. coli contain?

A

Approximately 80

29
Q

What 3 components make up ABC transporters?

A

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

30
Q

What is the role of the SBP in ABC transporters?

A

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

31
Q

What is the role of TMD in ABC transporters?

A

Substrate is transferred across transmembrane through TMD protein

32
Q

What is the role of NBD in ABC transporters?

A

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

33
Q

What is group translocation made up of?

A

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

34
Q

What molecules are group translocated?

A

Commonly sugars like fructose, glucose and mannose

35
Q

How does group translocation work?

A

The proteins in the system are alternatively phosphorylated and dephosphorylated until the final membrane-spanning protein receives the phosphate group and phosphorylates the sugar to be transported