Active transport uses energy to pump molecules against the concentration gradient. Active transport is accomplished by specific membrane proteins. Thus, various proteins of the membrane play a major role in both active and passive transport. A pump is a type of protein that uses energy to move substances across the membrane. These pumps can transport protein substances from a low concentration to a high concentration. The speed of transport is maximum when all the transporting proteins are being used or even if they are saturated. Like enzymes, carrier proteins are highly specific for the substances that cross the membrane. It is also sensitive to protein inhibitors that react with side chains.
