CH 5: Bacterial membranes and transport

Cell membrane

• Barrier between “in” and “out”

• Made up of Phospholipid Bilayer with embedded or associated Proteins

Cell membrane functions

1) Support for external structures

2) Signaling and communication

3) Export of toxins and other virulence factors

4) Transport of substances in and out of the cell

5) Establishment of concentration gradients for energy transer

Passive Transport

• Moves nutrients with concentration gradient (High→low)

• Net movement of molecules until equilibrium is reach

Simple diffusion (passive)

Direct transport through the phospholipid membrane

Facilitated diffusion (passive)

A protein channel or carrier is used

Active transport

• Moves nutrients against the concentration gradient (low→high)

• Therefore, requires an input of ENERGY

4 types energy sources

1) ATP: Primary transport and ABC transporters

2) Gradient of another molecule: Coupled Transport

3) Light: Light driven pumps

4) High energy metabolite (not ATP): Group translocation

Primary Transport and ABC transporters

• Use ATP hydrolysis

• ATP binding cassette

Siderophores

Helper molecules for scavenging scarce minerals like iron

Coupled transport (Aka secondary transport)

Uses energy directly from an existing chemical gradient

• Bacteria often uses H+

1) Symport

2) Antiport

Symport

Both moving in or both moving out

Antiport

One moving in and one moving out

Group Translocation (aka Phosphotransferase System)

Uses energy from high energy organic compound in the cell to power transport

• PEP here (NOT ATP)

Transported molecule is modified (Phosphorylated)

• Transporter transfers a phosphate to the molecule that is being imported

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_____ of proteins, DNA, and other ____ _____ is curcial for bacteria to survive in a particular environment

Secretion; large molecules

Bacteria have several types of complex, multiprotein _____ ______ and ______ ______

Secretion systems; Efflux pumps (transporters that expel toxic substances

• Secretion requires ATP

Secretion of proteins is directed by a specific amino acid tag or a _______

Signal Sequence