Transport and Bacterial Cells
Uptake of Nutrients and Key
molecules
Microbiology 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- membranescomparative terms
• Hypertonic – refers to an environment with
higher salt concentration and lower water
potential
• Hypotonic – higher water concentration
( water potential) and lower solute
Isotonic – 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/0
470003790/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 Transport
http://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