The rate-limiting step for the secretion of secretory proteins or the appearance at the plasma membrane for membrane protein is generally thought to be the rate of exit from the ER. Biosynthesis in or at the ER, including folding, modifications, and assembly, hence is the most crucial step for efficient secretion.
When comparing fossils found in undisturbed layers of ground the most common conclusion is the age of the fossils. More specifically, in this way can be seen the time period in which the fossils found were living, and also the approximate age of them. By comparing them, can be seen the evolution of them, and what has caused it.
