Download Transport Group work

Biology 260
Stage 02 – Colonization and Infection
Building a model to explain transport of nutrients into a bacterial cell
Natural Phenomenon: A few bacteria have entered your body and a short time later they have multiplied to
colonize (or infect) you! How do they do this??
What is a model?
In science models are a set of ideas that, together, are used to try to explain how natural phenomena might
work. A model may be a graph, a diagram, a set of ideas set down in words, or anything that can be used to
represent the phenomenon. For example, a drawing of a cell is not a real cell, but helps us to explain what a
real cell might look like. Another example is a flow diagram of a metabolic pathway like glycolysis. Although
it is not the real molecules going through real chemical reactions, it helps us to explain how the metabolic
pathway works. Both of these are models that, although they are not the real biological phenomena, they
represent the phenomena and help us to explain how they work. Your textbook is FULL of models!! How
were these models created? A scientist or a team of scientists would write down their initial model (a set of
ideas of how they think something might work), test that model through library research and experimentation,
revise their model as new knowledge is learned, and then go through the process of testing and revising again
and again. Hopefully, through this iterative process of creating, testing, and revising, their model comes closer
and closer to explaining how that phenomenon actually works in nature. Models can then be used to predict
how your system might respond if you perturbed it in some specific way.
So far in our story…
A prokaryotic cell grows by binary fission in order to colonize or infect a host. To do this it needs to
1. adhere to the host, get past the normal microbiota, (and subvert the immune system (that’s Stage 04)),
2. have the right environment, and
3. transport in the nutrients that they need
To write the third part of this story, we must first follow nutrients, molecules, and ions as they are transported
across the cell membrane so that they can be used for metabolism (the next part of our story).
Transport across the cell membrane:
With your group, draw a skeleton model of a typical bacterial cell and indicate how the membrane functions to
regulate nutrient transport, oxygen and carbon dioxide transport, and a hydrogen ion electrochemical gradient
across the cell membrane.
Be sure to include ALL of the following:
 A drawing of the cytoplasmic membrane and cell wall of a Gram negative bacterial cell:
o Cell wall: Peptidoglycan layer plus outer membrane for Gram negative cells (don’t forget about
the porins in the outer membrane!)
o Cytoplasmic membrane: Phospholipid bilayer plus transport channel proteins
 Drawing and accompanying explanation about how the process works indicates how the membrane
regulates
o Nutrient transport into the cell through
 Facilitated diffusion
 Active transport
• Driven by proton motive force
• Driven by ATP (ABC Transporters)
 Group Translocation
o Oxygen and carbon dioxide transport into and out of the cell through
 Simple diffusion
o Hydrogen ion electrochemical gradient (proton motive force) across the cell membrane through
 Electron transport chain