TRANSPORT SYSTEMS

By: Kyle Losin and Veronica Swanberg

What Are Transport Systems? The set of proteins, enzymes, and

chemical messengers needed to move substances that are essential to basic cellular functioning into or out of the cell.

Why are Transport Systems Necessary?

Cells need a way of getting the nutrients needed for growth

Most cells live under conditions in which many of their essential nutrients are lacking, so there needs to be a way to get the few nutrients available into the cell and keep them there

Not all substances are able to move freely through the phospholipid bilayer of the cell; there needs to be a way to get these substances in

Types of Transport Systems

Passive transport

Facilitated diffusion

Active Transport

Group Translocation

Co-transport

Passive Transport

Also referred to as “Simple Diffusion” Solute particles move from an area of high

solute concentration to an area of low solute concentration In order to do this the solutes must be able to

freely penetrate the cellular membrane, i.e. glycerol

The rate of diffusion declines as more solute accumulates inside the cell unless it is used or modified in some way

Large, ionic, or polar molecules cannot be transported passively

Osmosis

Osmosis is a kind of passive diffusion in which the solute moving is water

Hypotonic (low osmotic concentration) or Hypertonic (high osmotic concentration) environments can be harmful to microbes by causing excessive swelling or shrinking

Some prokaryotes manage the level of water by using mechanosensitive channels or compatible solutes These channels allow solutes to move out of

cell to prevent swelling.

Facilitated Diffusion

Very similar to simple diffusion

Membrane protein is needed for solute to cross the cellular membrane Permeases

The rate of diffusion is dependent on the concentration of solute as well as the number of available membrane proteins to shuttle the solutes

Protein is thought to change its morphology temporarily in order to move the solutes across the membrane

Active Transport

Type of transport used to move solutes from an area of low solute concentration to an area of high solute concentration (i.e. against the concentration gradient)

It is similar to facilitated diffusion in that it uses transmembrane proteins to assist moving solutes into the cell

Key Distinction: ATP is necessary!

Sodium Potassium Pump

Group Translocation

Phosphoenolpyruvate: Sugar Phosphotransferase System (PTS) Uses a phosphorelay system to transfer a

phosphate group from phosphoenol pyruvate to incoming glucose via intermediate enzymes EI, HPr, EIIA, and EIIB

The goal is to modify glucose so more glucose can continually enter the cell

Uses Le Chatelier’s principle to achieve this goal

PTS system is very common in bacteria

Phosphotransferase System

Co-transport Systems

A type of active transport that is powered by a proton gradient

Symport Two different

substances are moved across the membrane in the same direction

Lactose permease in E. coli

Antiport One substances

moves out of the cell which allows another to move into the cell

References

TextWilley, Joanne M., Linda Sherwood, Christopher J. Woolverton

and Lansing M. Prescott. “Microbial Nutrition.”Prescott’s Principles of Microbiology. 1st ed. Boston: McGraw-

Hill HigherEducation, 2009. 114-18. Print.

Graphics PTS

http://spin.niddk.nih.gov/clore/Structures/E1-HPr/pts.gif Facilitated diffusion

http://www.ncbi.nlm.nih.gov/books/NBK9847/ Symport/Antiport

http://library.thinkquest.org/C004535/cell_membranes.html Osmosis

https://www.msu.edu/~kommkris/webquest/webquest-index.html Sodium Potassium Pump

http://schoolworkhelper.net/2010/12/cell-transport-passive-active/