Transport and Bacterial CellsUptake of Nutrients and Key

moleculesMicrobiology 2008

What molecules are needed by the cell

• Carbon source( CO2, CH4, organic molecules)

• Nitrogen source( nitrogen compounds) amino acids , ammonia or ammonium

• Energy source

Passive Transport

• A few molecules that are small can pass through the phospholipid bilayer by the process of diffusion

• Passive transport does not require an energy input

Passive Transport

• The process of diffusion occurs when molecules or ions move from an area of greater concentration to an area of lower concentration

• The movement is down the concentration gradient

Diffusion

• Slow process• Based upon the free energy of the

molecules themselves• Very small molecules such as O2 and

CO2 move in this manner

Rate of diffusion

• The rate of diffusion is determined by the difference in concentration of the nutrients or molecules on the outside and the inside of the membrane

Osmosis

• The movement of water from an area of higher concentration to an area of lower concentration

Concentration

• The amount of solute dissolved in an ml or Liter( known volume) of solvent

• Can be measured in moles per 1000 g solvent( water) which is referred to as molality(m)

• Can be measured in % solute/solution• Can be measured in Molarity – moles per liter

of solution( M)

Water Potential

• Higher potential energy of water• Higher concentration of water

molecules that have free energy of movement

Osmosis and cell- membranes- comparative terms

• Hypertonic – refers to an environment with higher salt concentration and lower water potential

• Hypotonic – higher water concentration( water potential) and lower soluteIsotonic – equal concentration of solute on

both sides of a membrane

Plasmolysis and Recovery

• Lysis of cell wall

Animations for classroom

• http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm

Membrane Proteins and Transport

Channels- moves one molecule in one direction across the membrane

without the expenditure of energy

• Ions and larger molecules can also diffuse• Many of these move through proteins that have

a hydrophilic interior or core• They move from high concentration to an area

of lower concentration• No energy is utilized• Channels are specific for just one ion or

molecule

Channels

• http://www.cellsalive.com/channels.htm

Membrane

Facilitated diffusion

• Facilitated diffusion is a type of diffusion which uses a transport molecule .

• Permease are proteins which are embedded in the cell membrane

• They assist in the movement of other molecules across the membrane

• This is a speedier process than regular diffusion, but again is highly specific

• No energy is spent in the process

Facilitated Diffusion

Aquaporins

• A major permease in bacteria is an aquaporin that helps to move water in and out of the cell

MIPs - Major Intrinisic proteins

• Group of proteins- They facilitate transport by changining their shape or conformation when they pick up the molecule

• When they move the molecule to the opposite side of the membrane they again change their shape upon release of the molecule they have transported

Active Transporthttp://staff.jccc.net/PDECELL/cells/activet.html

• Transport of molecules and ions against the concentration gradient from low concentration to high concentration

• Requires the input of energy in the form of ATP

• ATP ADP + P + energy

ATP Binding Cassette Transporters( ABC

Transporters)• Transporters are proteins that span the

membrane• They bind to the ATP and hydrolyze or

break down ATP to produce energy

Symports

• Move two molecules or a molecule and an ion in the same direction

• Both can move in the same direction• Usually one moves with the concentration

gradient• The other is pulled across the membrane

against the concentration gradient by the free energy of the molecules that are moving

Antiports

• Two molecules are moving across the membrane

• One molecule is moving against the concentration gradient in one direction

• The other is moving with the concentration gradient

Siderophores

• Iron is a very important nutritional ion for the bacterial cell

• Siderophores are small molecules that are able to form a complex with iron to bring it into the cell

Porins

• Porins are proteins located in the outer cell membranes ( the outer lipid membane)

• They are responsible for moving molecules through the outer membrane in Gram negative bacteria

• Molecules are moved into the periplasmic space and then into the cell

Group Translocation

• In this process the molecules are modified as they are transported across the cell membrane or into the cell

• Group Translocation is a type of active transport

• Many vital molecules are brought into the cell in this manner

Group Translocation

• Group Translocation involves the transfer of a phosphate group

• This energizes the molecule so that it can be transported into the cell

Protein Transport Systems in the Cell Membrane