Lecture 1: Solute Transport - Exam 3 Flashcards
What is the difference between Primary Transport and Secondary Transport?
Primary: Export driven by an exergonic reaction - proton transport.
H+in + energy -> H+out
Secondary: Is indirectly coupled to primary transport by an energy-yielding chemical reaction by ion currents (proton or sodium gradient)
H+out + Soluteout -> H+in + Solutein
What does the phospholipid bilayer allow the cell to do? Why is it important for the cell?
The phospholipid bilayer of the bacterial cell membrane acts as a barrier that blocks the diffusion of water-soluble molecules into and out of the cell. It allows bacteria to maintain an internal environment different from the external environment.
Metabolites can be maintained at intracellular concentration that is orders of magnitude _______ than extracellular concentrations.
What does this promote and allow?
Higher
This promotes more rapid enzymatic reactions and allows for retention of metabolic intermediates within the cell.
How does the phospholipid bilayer affect solute transport?
The phospholipid bilayer minimizes the passive diffusion of ion, including protons, allowing the membrane to maintain electrochemical proton and sodium ion gradients.
The membrane is able to maintain electrochemical proton and sodium ion gradients. The gradients do what?
The gradients drive ATP synthesis, solute transport, and other membrane activities.
The phospholipid bilayer is a permeability barrier, anything that is not _________ soluble must enter the cell through _________. Including:
Lipid ;
Integral membrane proteins
Including transporters, carriers, permeases, and porters.
Bacterial cell membranes consist in large part of a phospholipid matrix that acts as a permeable barrier blocking the diffusion of water-soluble molecules into and out of cells. Why do we care?
1) Metabolism - need to bring nutrients inside before eating them (catabolism), and remove waste products.
2) Multidrug resistance - preventing uptake, or pumping drugs out of the cell can confer resistance to antimicrobial compounds.
Describe solute transport in G- bacteria.
Solutes must pass through outer membrane and inner membrane (cell membrane).
Describe the transport of SMALL molecules through the OUTER membrane.
Transport of small molecules through the outer membrane occurs through Porins.
Porins are outer membrane proteins that form narrow channels for free diffusion of small hydrophilic molecules (< 600-700 Da) into the periplasm.
What kind of molecules are transported through porins?
Sugars, amino acids, ions etc are transported to the periplasm through porin channels.
Describe the transport of LARGER solutes in gram negative bacteria.
Transport of larger solutes require specific transport proteins such as TonB-dependent proteins.
What kinds of molecules require specific transport proteins in gram-negative bacteria?
Cobalamin, siderophores, oligosaccharides require specific transport proteins.
Describe solute transport in Gram Positive bacteria.
Solutes must pass through the cell membrane.
Biological membranes are _________ (hydrophobic/hydrophilic) making them impermeable to most water-soluble molecules. What is the major advantage and disadvantage of this.
Hydrophobic
Major advantage: separation of cytoplasm from environment, enables membrane potential
Major disadvantage: need specific mechanisms for solute transport.
Solute transport is _______ (with/against) solute gradient. Meaning what?
Against, this means energy is required.
The rate of solute uptake is directly proportional to…?
The extent of saturation of the transporters.
What is the affinity constant (Km)?
The concentration of solute that produces 1/2 the maximum initial rate of transport (1/2 Vm).
It is called the affinity constant because the Km is considered to be a measure of the affinity of the solute for transporter.
Is Km the same for evert transporter?
NO!